WO2025245584A1

WO2025245584A1 - Power management in a network of sensing nodes

Info

Publication number: WO2025245584A1
Application number: PCT/AU2025/050578
Authority: WO
Inventors: Braeden BORG
Original assignee: Fleet Space Technologies Pty Ltd
Current assignee: Fleet Space Technologies Pty Ltd
Priority date: 2024-05-29
Filing date: 2025-05-29
Publication date: 2025-12-04
Anticipated expiration: 2026-11-29

Abstract

Some embodiments relate to a method of controlling seismic sensing nodes for ambient noise tomography (ANT). The method includes: transmitting a sensing initiation command simultaneously to a plurality of the seismic sensing nodes to cause the seismic sensing nodes to begin passive seismic sensing for ANT, each of the seismic sensing nodes being deployed as part of a spaced array of seismic sensing nodes, the spaced array extending across a region of interest, the seismic sensing nodes having their own respective power supplies, vibration sensors, and communication componentry; receiving sensor data from the seismic sensing nodes while the seismic sensing nodes remain deployed across the region; generating a geophysical model of a sub-ground region in the region of interest based on the received sensor data; and transmitting a sensing termination command simultaneously to the seismic sensing nodes to cause the seismic sensing nodes to stop the passive seismic sensing.

Description

POWER MANAGEMENT IN A NETWORK OF SENSING NODES

FIELD

[0001] Embodiments relate to data acquisition units, also referred to as seismic sensing nodes, seismic data acquisition nodes, or seismic data acquisition units. More specifically, embodiments relate to seismic sensing nodes for use in data gathering for ambient noise tomography (ANT). Some embodiments relate to a method of controlling seismic sensing nodes for ANT, and systems employing one or more seismic sensing nodes.

[0002] Data acquisition units may include any geophysical device configured to measure physical properties of the Earth and to transmit data representing the measured physical properties to a satellite network.

BACKGROUND

[0003] Data acquisition for ambient noise tomography processing can be a time-consuming endeavour. Ambient noise tomography requires continuous sampling. There may be significant latency from deploying data acquisition sensors and subsequently collecting the data measured from the data acquisition sensors to producing ambient noise tomography images, which can take from several weeks to several months.

[0004] Furthermore, the data acquisition units for ambient noise tomography may need to be deployed in remote and/or harsh environments which can present various challenges.

Some data acquisition units may malfunction, may be degraded, may not be functioning correctly, may display behaviour that is anomalous or that deviates from a normal operation, or may otherwise fail to meet sensor performance requirements. There is a risk that such units may transmit bad data, leading to the generation of inaccurate models. There is also a risk that failure of some units may cause a situation where there is an insufficient number of operating data acquisition units to generate an accurate model.

[0005] In remote and harsh environments without a power supply, there may be data storage and power constraints associated with data acquisition for ambient noise tomography. Data acquisition units for ambient noise tomography may be difficult and/or time consuming to deploy. There is a risk that the respective power supplies of some of the data acquisition units may deplete while the remaining data acquisition units in an array of data acquisition units are deployed.

[0006] Furthermore, the data acquisition units within an array are usually geographically separated from each other. Once sufficient data has been obtained from the data acquisition units, it is potentially a time-consuming process to power down individual units to conserve battery life. In some cases, it may be necessary to power down individual units on detecting low battery and/or poor logistics.

[0007] One or more embodiments of the present disclosure address or ameliorate at least one disadvantage or shortcoming of prior techniques, or at least provide a useful alternative thereto.

[0008] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each of the appended claims.

SUMMARY

[0009] Some embodiments of the present disclosure relate to a method of controlling seismic sensing nodes for ambient noise tomography (ANT). The method comprises: transmitting a sensing initiation command simultaneously to a plurality of the data acquisition units to cause the data acquisition units to begin passive seismic sensing for ANT, each of the data acquisition units being deployed as part of a spaced array of data acquisition units, the spaced array extending across a region of interest, wherein each data acquisition unit has its own power supply vibration sensor and communication componentry; receiving sensor data from the seismic data acquisition nodes while the data acquisition units remain deployed across the region; generating a geophysical model of a sub-ground region in the region of interest based on the received sensor data; and transmitting a sensing termination command simultaneously to the seismic data acquisition nodes to cause the seismic data acquisition nodes to stop the passive seismic sensing.

[0010] The term 'comprising' as used in this specification means 'consisting at least in part of'. When interpreting each statement in this specification that includes the term 'comprising', features other than that or those prefaced by the term may also be present. Related terms such as 'comprise' and 'comprises' are to be interpreted in the same manner.

[0011] The receiving may include receiving the sensor data via at least one satellite. The receiving may include receiving the sensor data via at least one low earth orbit satellite and/or at least one geostationary satellite.

[0012] The transmitting may be performed by a server in wireless communication with the seismic sensing nodes via one or more satellites.

[0013] The sensing termination command may cause each of the seismic sensing nodes to enter a low-power standby mode in which passive seismic sensing is not performed by the seismic sensing nodes.

[0014] The method may further include, prior to transmitting the sensing initiation command, registering each of the seismic sensing nodes as part of the array and receiving an indication that each seismic sensing node in the array is in low-power standby mode.

[0015] The method may further include, after the registering and prior to transmitting the sensing initiation command, deploying the seismic sensing nodes in the spaced array.

[0016] The method may further include monitoring the geophysical model as it is generated to determine whether at least one data criterion is met, wherein the sensing termination command is transmitted in response to determining that the at least one data criterion has been met.

[0017] The at least one criterion may include one or more of: a calculated signal to noise ratio of the sensor data; a calculated cross-correlation signal to noise ratio representative of at least one of the data acquisition units within the spaced array; a model spatial resolution criterion of at least part of a model volume of the sub-ground region; a threshold time duration; a threshold number of data acquisition units that are operating within the spaced array; or a threshold battery capacity among at least one of the data acquisition units within the spaced array.

[0018] The receiving may include receiving sensor data over a plurality of days between about 3 days and about 12 days.

[0019] The receiving may include receiving the sensor data continuously until the sensing termination command causes the seismic sensing nodes to stop seismic sensing.

[0020] The received sensor data may be 1-bit normalised data.

[0021] The communication componentry may include a wireless modem. The wireless modem may include a satellite modem.

[0022] The method may further include, after transmitting the sensing termination command, redeploying the seismic sensing nodes in a redeployed spaced array of the seismic sensing nodes to perform ANT in a different region of interest.

[0023] The redeploying may be performed without recharging the seismic sensing nodes.

[0024] The method may further include, after the redeploying, transmitting a further sensing initiation command to cause some or all of the redeployed array of seismic sensing nodes to begin passive sensing of seismic vibrations to generate further sensor data in relation to the different region of interest.

[0025] The method may further include generating a further geophysical model of a subground region in the different region of interest based on the received further sensor data; and transmitting a further sensing termination command simultaneously to the seismic sensing nodes in the redeployed array to cause the seismic sensing nodes to stop the passive seismic sensing. [0026] The method may further include receiving operational status data from each of the seismic sensing nodes, the operational status data including at least one of: node location data; node orientation data; node battery level data; electronics temperature data, or node operational fault data.

[0027] Described herein is a system for ambient noise tomography (ANT). The system includes: processing circuitry; and memory storing program code that, when executed by processing circuity, causes the processing circuity to perform the foregoing method.

[0028] Some embodiments of the present disclosure relate to a system for ambient noise tomography. The system includes a server including processing circuitry and having access to memory. The memory stores program code that, when executed by processing circuity, causes the processing circuity to: transmit a sensing initiation command simultaneously to a plurality of the data acquisition units to cause the data acquisition units to begin passive seismic sensing for ANT, each of the data acquisition units being deployed as part of a spaced array of data acquisition units, the spaced array extending across a region of interest, wherein each data acquisition unit has its own power supply vibration sensor and communication componentry; receive sensor data from the seismic data acquisition nodes while the data acquisition units remain deployed across the region; generate a geophysical model of a subground region in the region of interest based on the received sensor data; and transmit a sensing termination command simultaneously to the seismic data acquisition nodes to cause the seismic data acquisition nodes to stop the passive seismic sensing.

[0029] The receiving performed by the processing circuitry may include receiving the sensor data via at least one satellite. The receiving performed by the processing circuitry may include receiving the sensor data via at least one low earth orbit satellite and/or at least one geostationary satellite.

[0030] The transmitting performed by the processing circuitry may be performed in wireless communication with the seismic sensing nodes via one or more satellites. [0031] The sensing termination command may cause each of the seismic sensing nodes to enter a low-power standby mode in which passive seismic sensing is not performed by the seismic sensing nodes.

[0032] The program code may further cause the processing circuitry to, prior to the transmission of the sensing initiation command, register each of the seismic sensing nodes as part of the array and receive an indication that each seismic sensing nodes in the array is in low-power standby mode.

[0033] The program code may further cause the processing circuitry to monitor the geophysical model as it is generated to determine whether at least one data criterion is met, wherein the sensing termination command is transmitted in response to determining that the at least one data criterion has been met.

[0034] The at least one criterion may include one or more of: a calculated signal to noise ratio of the sensor data; a calculated cross-correlation signal to noise ratio representative of at least one of the data acquisition units within the spaced array; a model spatial resolution criterion of at least part of a model volume of the sub-ground region; a threshold time duration; a threshold number of data acquisition units that are operating within the spaced array; or a threshold battery capacity among at least one of the data acquisition units within the spaced array.

[0035] The receiving may include receiving sensor data over a plurality of days between about 3 days and about 12 days.

[0036] The receiving may include receiving the sensor data continuously until the sensing termination command causes the seismic sensing nodes to stop seismic sensing.

[0037] The received sensor data may be 1-bit normalised data.

[0038] The program code may further cause the processing circuitry to, after redeployment of the seismic sensing nodes in a redeployed spaced array of the seismic sensing nodes to perform ANT in a different region of interest, transmit a further sensing initiation command to cause some or all of the redeployed array of seismic sensing nodes to begin passive sensing of seismic vibrations to generate further sensor data in relation to the different region of interest.

[0039] The program code may further cause the processing circuitry to: generate a further geophysical model of a sub-ground region in the different region of interest based on received further sensor data; and transmit a further sensing termination command simultaneously to the seismic sensing nodes in the redeployed array to cause the seismic sensing nodes to stop the passive seismic sensing.

[0040] The program code may further cause the processing circuitry to receive operational status data from each of the seismic sensing nodes, the operation status data including at least one of: node location data; node orientation data; node battery level data; electronics temperature data, or node operational fault data.

[0041] Some embodiments of the present disclosure relate to a method of controlling a plurality of seismic sensing nodes for ambient noise tomography (ANT), at least some of the seismic sensing nodes being deployed as part of a spaced array of seismic sensing nodes, the spaced array extending across a region of interest, wherein the seismic sensing nodes have their own respective power supplies, vibration sensors, and communication componentry. The method includes: at least some of the seismic sensing nodes in the spaced array receiving a sensing initiation command simultaneously, to cause the seismic sensing nodes to begin passive seismic sensing for ANT; transmitting sensor data generated from the passive seismic sensing performed by the seismic sensing nodes while the seismic sensing nodes remain deployed across the region, for generation of a geophysical model of a sub-ground region in the region of interest based on the received sensor data; at least some of the seismic sensing nodes in the spaced array receiving a sensing termination command simultaneously, to cause those seismic sensing nodes that are performing the passive seismic sensing to stop the passive seismic sensing.

[0042] Some embodiments of the present disclosure relate to a system for ambient noise tomography including a plurality of seismic sensing nodes for ambient noise tomography (ANT), the seismic sensing nodes having their own respective power supplies, vibration sensors, and communication componentry, the communication componentry configured to perform the foregoing method.

[0043] Some embodiments of the present disclosure relate to a system for ambient noise tomography including: a plurality of seismic sensing nodes for ambient noise tomography (ANT), the seismic sensing nodes having their own respective power supplies, vibration sensors, and communication componentry, at least some of the seismic sensing nodes deployed as part of a spaced array of seismic sensing nodes, the spaced array extending across a region of interest. The communication componentry is configured to: receive a sensing initiation command simultaneously, to cause the seismic sensing nodes to begin passive seismic sensing for ANT; transmit sensor data generated from the passive seismic sensing performed by the seismic sensing nodes while the seismic sensing nodes remain deployed across the region, for generation of a geophysical model of a sub-ground region in the region of interest based on the received sensor data; and receive a sensing termination command simultaneously, to cause those seismic sensing nodes that are performing the passive seismic sensing to stop the passive seismic sensing.

[0044] Some embodiments of the present disclosure relate to a method of controlling a plurality of seismic sensing nodes for ambient noise tomography (ANT), by a server in communication with the plurality of seismic sensing nodes, the server including processing circuitry and having access to memory. The method includes: the server transmitting a sensing initiation command simultaneously to a plurality of the seismic sensing nodes, each of the seismic sensing nodes being deployed as part of a spaced array of seismic sensing nodes, the spaced array extending across a region of interest, the seismic sensing nodes having their own respective power supplies, vibration sensors, and communication componentry; at least some of the seismic sensing nodes in the spaced array receiving the sensing initiation command simultaneously, to cause the seismic sensing nodes to begin passive seismic sensing for ANT; at least some of the seismic sensing nodes transmitting sensor data generated from the passive seismic sensing performed by the seismic sensing nodes while the seismic sensing nodes remain deployed across the region; the server receiving sensor data from the seismic sensing nodes while the seismic sensing nodes remain deployed across the region; the server generating a geophysical model of a sub-ground region in the region of interest based on the received sensor data; and the server transmitting a sensing termination command simultaneously to the seismic sensing nodes; at least some of the seismic sensing nodes in the spaced array receiving the sensing termination command simultaneously, to cause those seismic sensing nodes that are performing the passive seismic sensing to stop the passive seismic sensing.

[0045] Some embodiments of the present disclosure relate to a system for ambient noise tomography including: a server including processing circuitry and having access to memory; and a plurality of seismic sensing nodes for ambient noise tomography (ANT), the seismic sensing nodes having their own respective power supplies, vibration sensors, and communication componentry, at least some of the seismic sensing nodes deployed as part of a spaced array of seismic sensing nodes, the spaced array extending across a region of interest. The memory stores program code that, when executed by the processing circuity, causes the processing circuity to: transmit a sensing initiation command simultaneously to a plurality of the seismic sensing nodes to cause the seismic sensing nodes to begin passive seismic sensing for ANT; receive sensor data from the seismic sensing nodes while the seismic sensing nodes remain deployed across the region; generate a geophysical model of a subground region in the region of interest based on the received sensor data; and transmit a sensing termination command simultaneously to the seismic sensing nodes to cause the seismic sensing nodes to stop the passive seismic sensing. The communication componentry of each seismic sensing node is configured to: receive the sensing initiation command, to cause the seismic sensing nodes to begin passive seismic sensing for ANT; transmit sensor data generated from the passive seismic sensing performed by the seismic sensing nodes while the seismic sensing nodes remain deployed across the region; and receive the sensing termination command, to cause those seismic sensing nodes that are performing the passive seismic sensing to stop the passive seismic sensing.

[0046] Some embodiments of the present disclosure relate to a method of controlling geophysical sensing nodes, the method comprising: transmitting a sensing initiation command simultaneously to a plurality of the sensing nodes to cause the sensing nodes to begin passive measurement, the sensing nodes being deployed as part of a spaced array of sensing nodes, the spaced array extending across a region of interest, the sensing nodes having their own respective power supplies, sensors, and communication componentry; receiving sensor measurement data from the sensing nodes while the sensing nodes remain deployed across the region; receiving sensor performance data from a plurality of the sensing nodes; generating a geophysical model of a sub-ground region in the region of interest based on the received sensor measurement data; and responsive to determining, based on the sensor performance data, that at least one of the sensing nodes is degraded, transmitting a sensing termination command to the at least one degraded sensing node to cause the at least one degraded sensing node to stop the passive measurement.

[0047] The sensor performance data may include power consumption, the method further comprising determining that at least one sensing node is degraded on determining that a power consumption of the at least one sensing node is above a normal power consumption range.

[0048] The sensor performance data may include software uptime, the method further comprising determining that at least one sensing node is degraded on determining that a software uptime is below an expected software uptime range.

[0049] The method may further include: monitoring the geophysical model as it is generated to determine whether at least one model quality criterion is met; and responsive to determining that the at least one model quality criterion has been met, transmitting a sensing termination command to the sensing nodes to cause the sensing nodes to stop the passive measurement.

[0050] The at least one model quality criterion may include one or more of: a calculated signal to noise ratio of the sensor measurement data; a calculated cross-correlation signal to noise ratio representative of at least one of the sensing nodes within the spaced array; a model spatial resolution criterion of at least part of a model volume of the sub-ground region; a threshold time duration; a threshold number of sensing nodes that are operating within the spaced array; or a threshold battery capacity among at least one of the sensing nodes within the spaced array.

[0051] Some embodiments of the present disclosure relate to a geophysical sensing system comprising: a server including processing circuitry and having access to memory; wherein the memory stores program code that, when executed by the processing circuity, causes the processing circuity to: transmit a sensing initiation command simultaneously to a plurality of the sensing nodes to cause the sensing nodes to begin passive measurement, the sensing nodes being deployed as part of a spaced array of sensing nodes, the spaced array extending across a region of interest, the sensing nodes having their own respective power supplies, vibration sensors, and communication componentry; receive sensor measurement data from the sensing nodes while the sensing nodes remain deployed across the region; receive sensor performance data from a plurality of the sensing nodes; generate a geophysical model of a sub-ground region in the region of interest based on the received sensor measurement data; and responsive to determining, based on the sensor performance data, that at least one of the sensing nodes is degraded, transmit a sensing termination command to the at least one degraded sensing node to cause the at least one degraded sensing node to stop the passive measurement.

[0052] The sensor performance data may include power consumption. The program code may cause the processing circuitry to determine that at least one sensing node is degraded on determining that a power consumption of the at least one sensing node is above a normal power consumption range.

[0053] The sensor performance data may include software uptime. The program code may cause the processing circuitry to determine that at least one sensing node is degraded on determining that a software uptime is below an expected software uptime range.

[0054] The program code may cause the processing circuitry to: monitor the geophysical model as it is generated to determine whether at least one model quality criterion is met; and responsive to determining that the at least one model quality criterion has been met, transmit a sensing termination command to the sensing nodes to cause the sensing nodes to stop the passive measurement.

[0055] The at least one model quality criterion may include one or more of: a calculated signal to noise ratio of the sensor measurement data; a calculated cross-correlation signal to noise ratio representative of at least one of the data acquisition units within the spaced array; a model spatial resolution criterion of at least part of a model volume of the sub-ground region; a threshold time duration; a threshold number of data acquisition units that are operating within the spaced array; or a threshold battery capacity among at least one of the data acquisition units within the spaced array.

BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 is a block diagram of a sub-surface tomography system according to some embodiments.

[0057] Figure 2 shows an exploded view of a data acquisition unit according to some embodiments.

[0058] Figure 3 shows an example of the tomography module of figure 1.

[0059] Figure 4 shows a method for initiating the data acquisition units of figures 1 and 2.

[0060] Figure 5 shows a method for controlling the data acquisition units of figures 1 and 2 performed by the server system of figure 1 according to some embodiments.

[0061] Figure 6 shows a method for controlling the data acquisition units of figures 1 and 2 performed by the data acquisition units according to some embodiments.

[0062] Figure 7 shows an example of a data packet for transmittal to a satellite of figure 1.

[0063] Figure 8 shows an example of a data packet for transmittal to the data acquisition unit of figure 1 and 2.

[0064] Figures 9A, 9B, and 9C show examples of geophysical models of a sub-ground region in a region of interest.

[0065] Figure 10 shows a further example of a geophysical model of a sub-ground region in a region of interest.

[0066] Figure 11 shows an example computer system. DETAILED DESCRIPTION OF EMBODIMENTS

[0067] Embodiments relate to data acquisition units or nodes and more specifically to seismic data acquisition units or nodes for use in data gathering for ambient noise tomography (ANT). Some embodiments relate to a method of controlling data acquisition units for ANT, and systems employing one or more data acquisition units. Data acquisition units may include any geophysical device configured to measure physical properties of the Earth and to transmit data representing the measured physical properties to a satellite network.

[0068] The data acquisition unit may be configured to sense vibrations in a ground area/region. The data acquisition unit may include a vibration transducer, such as a geophone. The vibration transducer is configured to convert sensed vibrations into an electrical signal. The data acquisition unit may include an analogue to digital converter, which may digitise the electrical signal. Other types of measurement include magnetotellurics, gravity, induced polarisation, and augmented seismic.

[0069] The data acquisition unit may include a processor which may pre-process the (digitised) electrical signal and process the pre-processed electrical signal into a data payload. The data acquisition unit may include a satellite modem that is configured to transmit the data payload to a satellite. These features are similar to those described in PCT patent specification WO 2023/164738 Al, and Australian patent application 2024901363, both of which this present specification incorporates entirely by reference.

[0070] The data acquisition units may be self-contained. The data acquisition units may be relatively compact. The data acquisition units may be easily deployed, redeployed, and/or removed due to their small form factor and low mass. The data acquisition units may be easily assembled and/or disassembled. The data acquisition units may be relatively economical for manufacturing. The data acquisition unit may house all utilised antennas, and therefore may mitigate or reduce one or more of: vandalism, the number of failure points, wear, and effects of weather. The data acquisition unit may have limited points of ingress, and thereby may better resist the effects of weather and debris. The data acquisition unit may utilise paint coatings selected to resist effects of extreme temperature. The data acquisition unit may utilise electronic components which help resist effects of extreme temperature. The internal physical layout of the data acquisition unit may help resist or mitigate negative functional effects of extreme temperature. The housing and/or components of data acquisition unit may comprise materials that may help resist the effects of extreme temperature. The data acquisition unit may utilise insulated cabling from the geophone, and this may assist in reducing the internal noise of the data acquisition unit. The data acquisition unit may have a cable length from the geophone to a PCBA that carries an analogue to digital converter of about 10 to 30 cm, for example. This limited cable length may assist in reducing the internal noise of the data acquisition unit.

[0071] According to some embodiments, the data acquisition units may be capable of direct radio communications with a low earth orbit (LEO) satellite network. In some other embodiments, the data acquisition unit may be capable of direct radio communication with a geostationary satellite and/or geostationary satellite network.

[0072] The data acquisition units may be capable of acquiring ground movement measurements, processing the measurement data, transmitting the data via the LEO satellite network to be received by a server system for ambient noise tomography processing in about 2 minutes to 2 hours depending on satellite availability, immediately after the data acquisition unit is deployed.

[0073] Thus, the embodiments allow near-real time reception of data from the data acquisition units, for example for ambient noise tomography purposes. In this context of geological feature observation (i.e. long time scale as opposed to high-speed computing), near-real time is intended to include periods of as low as around 1-2 minutes latency up to around 2-4 hours or 6-12 hours latency from vibration sensing to reception at the remote server. This allows images to be formed at remote client computing devices from the ambient noise tomography within a matter of days, such as around 4 days, as the received data accumulates to provide a higher and higher resolution image.

[0074] As soon as a data acquisition unit is placed, the unit can be turned on and operated so that ambient noise tomography processing can commence whilst other data acquisition units are added to the array of data acquisition units for imaging a sub-surface region according to some embodiments. The imaging and the sub-surface region which is imaged may be three dimensional (3D).

[0075] Ambient noise tomography images according to some embodiments may be available for viewing on a client device communicatively coupled to the server system within 24 hours (for low resolution) and more substantial (higher resolution) images within 4 to 5 days. The resolution and information richness of the ambient noise tomography images may be iteratively improved upon subsequent sampling and transmission of data from the data acquisition units over the sampling period of 4 to 10 days or 2 to 8 days, for example.

[0076] According to some embodiments the data acquisition units may be self-contained and include a ground sensing module, processor, memory, a power source, and an attachable satellite communications module. The self-containment of the data acquisition units may allow ease of field deployment, field re-deployment, and transport of the data acquisition units. This may help attain cost and time reductions associated with the deployment and transport of data acquisition units. The self-contained data acquisition unit including ground sensing module, processor, memory, a power source, and an attachable satellite communications module may have a mass between about 2 to 3 kgs, 3 to 4 kgs, or 4 to 5 kgs. In some embodiments, the self-contained data acquisition unit has a mass of about 5, 4.5, 4, 3.5, 3, 2.5, or 2 kgs.

[0077] In some embodiments, energy consumed by the data acquisition units may be measured in watt-hours (Wh) representing an amount of energy consumed when a unit uses 1 watt of power for 1 hour. The data acquisition unit may have an energy consumption between about 19 to 24 Wh, and the satellite modem used by the data acquisition unit may have a power consumption in a day of between about 9.6 to 9.8 Wh or about 0.4 to 0.41 W. In some embodiments, the data acquisition unit has an energy consumption of about 21.4 Wh in a day. According to some embodiments, the other electronics of the data acquisition unit may have a power draw between about 0.4 to 0.5 W.

[0078] In some embodiments, the satellite modem has a standby power consumption between about 0.15 to 0.20 W. In some embodiments, the satellite modem has a standby power consumption of about 0.17 W. In some embodiments, the satellite modem used by the data acquisition unit has a standby energy consumption in a day of between about 3 to 4.1 Wh. In some embodiments, the satellite modem used by the data acquisition unit has a standby energy consumption in a day of about 3.5 Wh.

[0079] In some embodiments, the satellite modem has a transmission power consumption between about 7.0 to 7.5 W. In some embodiments, the satellite modem has a transmission power consumption of about 7.3 W. In some embodiments, the satellite modem has a transmission power consumption in a day between about 3.0 to 3.6 Wh. In some embodiments, the satellite modem has a transmission power consumption in a day of about 3.5 Wh.

[0080] In some embodiments, the satellite modem has a received signal processing power consumption between about 0.8 to 1 W. In some embodiments, the satellite modem has a received signal processing power consumption of about 0.9 W. In some embodiments, the satellite modem has a received signal processing power consumption between about 2.7 to 2.8 Wh. In some embodiments, the satellite modem has a received signal processing power consumption of about 2.72 Wh.

[0081] In some other embodiments, alterations such as the selection of a modem with an average power consumption of about 0.26W, may reduce the power consumption of the data acquisition unit to less than 7 W, which may extend this timeframe to 11 days without any further (external) power source, for example. The operating temperature also may vary the operation time of the data acquisition unit without any further (external) power source. In temperatures less than 20 degrees Celsius, the data acquisition unit may operate for 7 days without any further (external) power source. The operation times of the data acquisition unit, without any further (external) power source, may be based on time between transmission peaks of about every 15 to 20 minutes, for example.

[0082] In some embodiments, the data acquisition unit is configured to transmit data payloads to the server system in transmission intervals over a day of a combined transmission time between about 25 to 30 minutes. In some embodiments, the transmission duty cycle may be about 2%. In some embodiments, the data acquisition unit is configured to transmit data payloads to server system with an average transmission time interval between about 10 minutes to 4 hours.

[0083] In some embodiments, data acquisition unit is configured to transmit consecutive data payloads with an average transmission time interval between about 10 minutes to 30 minutes. In some embodiments, data acquisition unit is configured to transmit consecutive data payloads with an average transmission time interval of about 10 minutes, 13 minutes, 16 minutes, 20 minutes 23 minutes, 26 minutes, 30 minutes, 45 minutes, 1 hour, 2 hours, 3 hours, or about 4 hours.

[0084] In some embodiments, the data acquisition unit is configured to receive data transmissions over scheduled and/or unscheduled reception intervals in a day of a combined reception time between about 180 minutes to 200 minutes. In some embodiments, the reception duty cycle may be about 12.5%. In some embodiments, the data acquisition unit may be in standby when satellite modem is not transmitting or receiving data. In some embodiments, the data acquisition unit is configured to be in standby over scheduled and/or unscheduled intervals in a day for a combined standby time between about 20 to 22 hours.

[0085] According to some embodiments, the payload size may be between about 2kB to 40 kB. According to some embodiments, the payload size may be about 2 kB or 4 kB.

[0086] The data acquisition unit may process and store sampled pre-processed data locally and then transmit the data. The transmission of this stored data may represent a transmission peak. This time between peaks may be referred to as a duty cycle.

[0087] The power source to reach the above operation times of the data acquisition unit without any further (external) power source may be about 580 to 600 Wh. In some embodiments, a lower capacity power source may be selected to achieve smaller durations of operation without any further (external) power source. For example, the data acquisition unit may be configured with a modem with average power consumption of about 0.45 W and a power source of about 81.5 Wh capacity to achieve 4 days of operation without any further (external) power source. [0088] In another example, the data acquisition unit may be configured with a modem with average power consumption of about 1.0 W and a power source of about 157.5 Wh capacity to achieve 4 days of operation without any further (external) power source.

[0089] In another example, the data acquisition unit may be configured with a modem with average power consumption of about 0.45 W and a power source of about 163 Wh capacity to achieve consecutive periods of 4 days of operation (8 days of operation total) without any further (external) power source.

[0090] In another example, the data acquisition unit may be configured with a modem with average power consumption of about 1.0 W and a power source of about 315 Wh capacity to achieve consecutive periods of 4 days of operation (8 days of operation total) without any further (external) power source.

[0091] The power, storage, and transmission requirements of this operation may be aided by preprocessing the acquired data (to drastically compress the data by 8:1 or 16:1 or 32:1, for example) from the ground sensing module. The power source may be or include a rechargeable battery pack, for example.

[0092] According to some embodiments, the data acquisition unit measures seismic vibration in the ground region near where it is deployed. A geophone element may be used to generate electrical signals proportional to the vibrational velocity induced in the sensor. This signal is digitised and stored in a data buffer. Ambient noise tomography usually requires a continuous stream of data. In addition, only the z-axis (coaxial with the local gravity vector) may be required.

[0093] The data acquisition unit may sample its single geophone every 50 milliseconds (20 Hz), for example. It may store each sample in a software buffer. This sample rate could be higher, but as will become clear, the higher the sample rate, the greater the processing capability (and non-volatile storage) needs to be. The software buffer may have a size to be able to hold 512 samples, for example. [0094] In some other embodiments, the buffer size may be 64, 128, 256, 512, or 1024 samples. Once the current buffer is full, the buffer contents are passed down into a sequence of digital signal processing functions. Whilst this processing is happening (taking up computer resources), new samples obtained from the geophone are inserted into a second buffer. As such, between these two buffers, one will always be used for the processing algorithms and the other will be used to receive new samples.

[0095] Figure 1 is a block diagram of a sub-surface tomography system 100 according to some embodiments.

[0096] The sub-surface tomography system 100 may also be described as a data acquisition system 100. The sub-surface tomography system 100 comprises a data acquisition unit array 115. Data acquisition unit array 115 may also be referred to as data acquisition array 115, or array 115. The data acquisition array 115 comprises one or more data acquisition units 110. The one or more data acquisition units 110 may be configured for passive seismic monitoring. The one or more data acquisition units 110 may also be referred to as a seismic data acquisition unit 110, vibration sensing apparatus 110, seismometer module 110, geophone apparatus 110, geologic instrument 110, data acquisition node 110, end-node 110, node device 110 or a sensor node 110.

[0097] The sub-surface tomography system 100 also comprises a satellite constellation 135. The satellite constellation 135 comprises one or more satellites 130. Each of the one or more satellites 130 may be a Low Earth Orbit (LEO) satellite 130. In some other embodiments, one or more of satellites 130 may be a Geostationary (GEO) satellite 130. The satellite 130 is configured to communicate with data acquisition unit(s) 110 over a communication link 118. In embodiments with more than one satellite 130, the communication link 118 may extend to the more than one satellite 130. The communication link 118 may not be a persistent communication link and if satellite 130 is not accessible to the data acquisition unit 110, the data acquisition unit 110 may await the resumption of the radio communication link 118 to continue communication of information.

[0098] Radio communication links 118 are radio links to satellites 130 orbiting the earth to communicate data acquired from the one or more data acquisition units 110 of the data acquisition array 115 and receive instructions or configuration information or firmware updates for the one or more seismic data acquisition units 110.

[0099] The sub-surface tomography system 100 also comprises one or more ground stations 140. The ground stations 140 receive communication from one or more satellites 130 of the satellite constellation 135 over a communication link 138. Communication link 138 may be referred to as ground station communications link 138. The communication link 138 may be facilitated by radio waves of suitable frequency according to the region where the ground station 140 is located.

[0100] The satellite 130 may be a LEO satellite that circles the earth approximately every 90-110 minutes, for example. With such orbiting satellites, a relatively smaller number of satellite ground stations 140 may be used to receive downlinks from satellite 130, or all the data transmitted by the one or more data acquisition units 110 of the data acquisition array 115.

[0101] In some embodiments, satellites 130 in a near polar orbit may be used and ground stations 140 may be located near each of the Earth's poles. This arrangement allows each satellite 130 to connect to a ground station 140 on almost every orbit, leaving the throughput latency no higher than around 45 minutes (half the time required to complete an orbit), for example. In some embodiments, ground stations may be located at lower latitudes with less harsh weather and transport, and easier access to power and communication links to the ground station 140.

[0102] The ground station 140 may comprise radio communication equipment necessary to communicate with the satellite 130 and a communication interface to relay received information to a server system 150 over a communications link 148. Communication link 148 may also be referred to as server system communications link 148. The communication link 148 may be a wired or wireless communication link to the internet available to the ground station 140 and to the server system 150.

[0103] The server system 150 may be accessible over the internet through an application or platform on a client device 160 over a conventional internet connection over the communication link 157. Client device 160 may be referred to as client computing device 160. Communication link 157 may be referred as client device communications link 157. The communications of server system 150 may be handled by a server system communications module. The client device 160 may be an end user computing device such as a desktop, laptop, mobile device, tablet, for example.

[0104] In an embodiment, server system 150 is configured to transmit data to, and receive data from, data acquisition array 115. In an embodiment, server system 150 is configured to transmit data to, and receive data from, one or more data acquisition units 110. The transmitting may be performed by the server system 150 in wireless communication with the data acquisition units 110 via satellite constellation 135 and/or via one or more satellites 130.

[0105] Server system 150 may be in communication with interface 170. Interface 170 may comprise, for example, a cloud-based interface that functions as a primary hub for managing data transmissions between server system 150 and interface 170. It will be appreciated that references in this patent specification to data transfer to/from server system 150 may include data transfer to/from interface 170.

[0106] Diagnostic information may also be communicated from data acquisition unit 110 via satellite 130 to server system 150, which may be accessible to client device 160. Client device 160 may be configured to have an application to visualize the diagnostic information of one or more data acquisition units 110.

[0107] In some embodiments, some or all of this diagnostic information is collected and sent by data acquisition unit(s) 110 periodically. In some embodiments, some or all of this diagnostic information is collected and sent by data acquisition unit(s) 110 upon an event such as upon connection/re-connection of link 118. In some embodiments, client device 160 is configured to send a request via server system 150, ground station 140, and satellite 130 to a data acquisition unit 110 to trigger the transmission (and optionally acquisition) of diagnostic information to server system 150, for access by client device 160.

[0108] The server system 150 may be configured to decode, decrypt and/or decompress communications originating from the data acquisition units 110 and received over the communication links 118, 138 and 148 and store any data from the communications in data storage 152. In some other embodiments, the server system 150 may receive communications originating from the data acquisition units 110 and store any data from the communications in data storage 152.

[0109] In some embodiments, server system 150 may further comprise a tomography module 154 (which includes program code) executable by a processor of the server system 150 or the tomography module 154 may be located separately and communicatively coupled to the server system 150 via link 153. Tomography module 154 may also be referred to as subsurface imaging module 154, or ambient noise tomography (ANT) module 154, for example.

[0110] When executed, tomography module 154 may read data from the communications originating from the data acquisition units stored in data storage 152. The tomography module 154 may perform sub-surface tomography processing using the read data from the data storage 152. The sub-surface tomography processing may comprise ambient noise tomography processing. After performing sub-surface tomography processing, the tomography module 154 may send the sub-surface tomography data via link 153 to be stored in data storage 152.

[0111] Sub-surface tomography data may be data that can be processed to generate one or more sub-surface tomography images. Sub-surface tomography data may be data that can be processed to generate one or more sub-surface tomography images, such as one or more 3-D sub-surface tomography images.

[0112] Server system 150 may comprise, or have access to, code for executing a data visualisation module 156. The data visualisation module 156 may be a platform accessible to client device 160. The data visualisation module 156 may read sub-surface tomography data from data storage 152. The data visualisation module 156 and/or client device 160 may process sub-surface tomography data to generate sub-surface tomography images to be viewed on client device 160. The generated sub-surface tomography images may be ambient noise tomography images. [0113] The sub-surface tomography system 100 enables high-latency communication of data between the data acquisition array 115 and the client device 160. High-latency communication may be inherently suitable for transmitting small messages to and from the data acquisition array 115 deployed in remote locations and the server system 150. High- latency communication may comprise a latency of greater than about 1 second, 2 seconds, 15 seconds, 30 seconds, or 1, 2, 3, 4 or 5 minutes, for example. Two examples of high-latency communication methods include store and forward communication, and short burst data communication.

[0114] Store and forward communication may be implemented by the satellite constellation 135 that periodically passes into a range where communication may be received from the data acquisition units 110 positioned in a remote location. Satellite 130 may gather data from the data acquisition units 110 and deliver it back to ground stations 140 that are connected to a network backbone or a network generally accessible over the internet.

[0115] Short Burst Data (SBD) is another technique for communicating short data messages between seismic data acquisition unit 110 and a centralised host computing system such as the server system 150. SBD satellite messaging systems work by waiting for a suitable slot in a satellite network that has voice as its primary application.

[0116] Examples include Orbcomm™, Iridium™ and Globalstar™. The voice traffic in such systems is prioritised and requires latencies typically less than 500 ms, for example. However, due to the fluctuating demands for voice traffic, there are windows in which shorter messages can be sent. This is analogous to the Short Messaging System (SMS) technique/standard used in terrestrial communications networks design for mobile telephony. The typical latencies of the SBD traffic in such systems can be in the range of 5 seconds to 10 minutes or greater, for example.

[0117] Figure 2 shows an exploded view of a data acquisition unit 110 according to some embodiments. Data acquisition unit 110 is configured to acquire data for performing passive seismic monitoring, such as for ambient noise tomography processing. Data acquisition unit 110 may be configured to continuously acquire seismic data over a long period. [0118] Data acquisition unit 110 includes a housing 220. The housing 220 may include an upper part 223. The housing 220 may include a lower part 226. The housing 220 includes a central chamber. In some embodiments, upper part 223 and lower part 226 define the central chamber. In some embodiments, upper part 223 and lower part 226 are attachable together to define the central chamber. Data acquisition unit 110 is self-contained when assembled.

[0119] Upper part 223 may include an upper part flange 225 protruding from a distal edge of the upper part 223. Lower part 226 may include a lower part flange 228 protruding from a distal edge of lower part 226.

[0120] Data acquisition unit 110 may include a wireless modem. One example of a wireless modem includes a satellite modem 290. Satellite modem 290 may be disposed at a top portion of the housing 220. The upper part 223 may comprise a satellite modem receiving portion 224 on an outer surface of upper part 223 for coupling, receiving, attaching, bearing, and/or including satellite modem 290. Satellite modem 290 may be referred to as satellite communications module 290. Satellite modem 290 may be a modem for communicating with one or more satellites 130 from satellite constellation 135. Accordingly, satellite modem 290 may be configured for low earth orbit (LEO) satellite communications. In some other embodiments, satellite modem 290 is configured for geostationary satellite communications.

[0121] Satellite modem 290 may include a housing. Satellite modem 290 may be self- contained. The housing of satellite modem 290 may have an ingress protection (IP) rating of 67. Satellite modem 290 may include a processor. Satellite modem 290 may include an inbuilt- antenna. Satellite modem 290 may be an Orbcomm, Iridium, Fleet Space, Inmarsat, or Gilat modem, for example. Satellite modem 290 may be an Orbcomm ST2100. The satellite modem 290 may have a mass between about 350 grams to 1 kg. According to some embodiments, the satellite modem may have a mass of about 400 grams.

[0122] Data acquisition unit 110 may include a satellite modem receiving portion 224, which in some embodiments may be a satellite modem receiving recess 224 and/or a satellite modem receiving feature 224, for receiving and/or mounting the satellite modem 290. The satellite modem receiving portion 224 and satellite modem receiving recess 224 may be located on a top surface of the upper part 223. The satellite modem receiving recess 224 may be 1 to 5 mm deep in the top surface of upper part 223. The satellite modem receiving portion 218 and satellite modem receiving recess 224 may have screw holes or other attachment features for securing satellite modem 290 to the top surface of the upper part 223/data acquisition unit 110.

[0123] The data acquisition unit 110 may include a power supply. The power supply may include power supply circuitry and/or connections on/to components on first PCBA 250 and/or second PCBA 255. Data acquisition unit 110 may include a power source 240. The power supply may include power source 240. The power supply may supply power from power source 240 to components of data acquisition unit 110 via circuitry and/or connections to components on first PCBA 250 and/or second PCBA 255, such as a processor. The power supply may include a voltage/power regulator.

[0124] Data acquisition unit 110 may include a cable recess 229. Upper part 223 may include cable recess 229. Satellite modem receiving portion 224 may include cable recess 229. Cable recess 229 may allow cabling for data communications and/or power to/from the satellite modem 290 from/to modem recess 534, modem port 535, first PCBA 250, second PCBA 255, and/or power source 240, for example. In some other embodiments, data acquisition unit 110 includes a cable port 229. Upper part 223 may include cable port 229. Satellite modem receiving portion 224 may include cable port 229. Cable port 229 may allow cabling for data communications and/or power to/from the satellite modem 290 from/to modem recess 534, modem port 535, first PCBA 250, second PCBA 255, and/or power source 240, for example.

[0125] Data acquisition unit 110 includes a vibration sensing portion 227 for sensing vibrations in the ground area/region. Vibration sensing portion 227 may be a probe or spike, for example. In some embodiments, the lower part 226 includes the vibration sensing portion 227. Vibration sensing portion 227 includes a narrowing (generally conical) distal tip at a lower extremity of the vibration sensing portion 227.

[0126] Data acquisition unit includes a component mounting structure 230. The component mounting structure 230 includes a mounting body for mounting components thereon. The mounting body of the component mounting structure 230 may be a unitary structure. Alternatively, component mounting structure 230 may include multiple pieces coupled together to form the mounting body. The component mounting structure 230 may comprise a single part or piece. The mounting body may include multiple sides or panels. The mounting body may include multiple opposed sides or panels. The opposed sides or panels define mounting portions and/or mounting surfaces to which components, such as PCBAs, antennas, sensors, conductors and/or batteries (as non-limiting examples), can be mounted. The component mounting structure 230 may be, consist of or include a single u-shaped piece.

[0127] The component mounting structure 230 may include a plurality of sides, panels or faces. The sides, panels or faces define an interior volume and define at least one opening to a part of the component mounting structure 230 that is exterior to the interior volume. According to some embodiments, the component mounting structure 230 has a hollow approximately cuboid shape. According to some embodiments, the component mounting structure 230 is a hollow cuboid shape that is missing two opposite faces, for example as shown in Figure 2 and Figure 6A. According to some other embodiments, the component mounting structure 230 comprises three concatenated sides or faces, shaped as a u-shape, as shown in Figure 6B.

[0128] According to some embodiments, as shown in Figure 2, the mounting body and/or the faces or sides of component mounting structure 230 may comprise recesses, openings or passages for allowing cabling to extend between components mounted to the component mounting structure 230 and other internal and/or external components, such as satellite modem 290, externally accessible switch components, charging or communication ports, and/or peripherals such as GPS modules. The recesses, openings or passages on component mounting structure 230 also serve to reduce the mass of the component mounting structure 230.

[0129] The component mounting structure 230 may be configured for receiving a power source 240 in the interior volume. Power source 240 may comprise at least one battery. Power source 240 may comprise one or more cells. Power source 240 may comprise a casing for one or more battery and/or storage cells. Power source 240 may comprise wiring between the one or more batteries and/or storage cells. Power source 240 may comprise a series and/or parallel arrangement of a plurality of storage cells. In some embodiments, power source 240 comprises 8 to 30 storage cells. In some embodiments, power source 240 comprises 3 series 3 parallel (3S3P) arrangement of storage cells. In some embodiments, power source 240 comprises 2S4P, 3S4P, 3S5P, 3S6P, 3S7P, 3S8P, 3S9P, or 3S10P arrangement of storage cells. In some embodiments, power source 240 comprises 3S8P arrangement of 24 storage cells. The arrangement of storage cells in series may be varied depending on the voltage requirements of the modem 290. The arrangement of storage cells may be varied depending on the individual cell voltage output for selected storage cells.

[0130] Power source 240 may have an energy storage capacity between about 100 Wh to 1250 Wh, for example. In some embodiments, power source 240 has an energy storage capacity of between about 85 Wh to 285 Wh, 240Wh to 285Wh, 100 Wh to 180 Wh, 150 Wh to 800 Wh, 150 Wh to 350 Wh, 300 Wh to 600 Wh, or 550 Wh to 800 Wh, for example. In some embodiments, power source 240 may have a minimum energy storage capacity of between about 100 Wh to about 140 Wh for continuous operation of about 4 to 5 days without any further (external) power source. This continuous operation time without any further (external) power source, may be dependent on modem 290 consuming about 0.17 W in standby, 0.9 W when receiving signals, and 7.3 W when transmitting. This continuous operation time without any further (external) power source, may be dependent on a modem 290 which consumes up to about 9 to 10 Wh of power. In some other embodiments, power source 240 has a maximum energy storage capacity of between about 1200 to 1250 Wh for continuous operation of about 60 days without any further (external) power source. In some embodiments, power source 240 has an energy storage of about 280Wh for at least 9 days of continuous operation. In some embodiments, power source 240 has an energy storage of about 280Wh for at least two deployment cycles, each deployment cycle having a duration for at least 4 days. This allows the data acquisition unit 110 to be used in one location for one deployment cycle of multiple days and then moved to another location for a second deployment cycle of multiple days.

[0131] In some embodiments, power source 240 has an energy storage capacity of about 110 Wh to 150 Wh for continuous operation of about 4 to 5 days without any further (external) power source. In some embodiments, power source 240 may have an energy storage capacity of between about 220 and 300 Wh for continuous operation of about 8 to 11 days without any further (external) power source. Such energy storage capacities may allow seismic data acquisition unit 110 to acquire enough ground movement data in at least two different sites (i.e., deployed at one site for a period and then redeployed at another site for another period) for production of respective sub-surface images of the respective subsurfaces of the sites. This continuous operation time without any further (external) power source, may be dependent on a satellite modem 290 which consumes about or less than 0.6 W of power.

[0132] In some embodiments, power source 240 has a capacity between about 260 Wh to 310 Wh for about 9 to 12 days of continuous operation. In some embodiments, power source 240 has a capacity of about 280 Wh for about 9 to 10 days of continuous operation. In some embodiments, power source 240 has a capacity of about 160 Wh to 220 Wh for about 7 days of continuous operation. In some embodiments, power source 240 has a capacity of about 215 Wh for about 7 days of continuous operation.

[0133] The component mounting structure 230 may be configured for mounting electronics. The component mounting structure 230 may include one or more panels on the exterior of component mounting structure 230 for mounting electronics. The component mounting structure 230 may be configured for mounting a first printed circuit board assembly (PCBA) 250. Component mounting structure 230 may mount first PCBA 250 on a first exterior panel of component mounting structure 230. The component mounting structure 230 may be configured for mounting a second PCBA 255. Component mounting structure 230 may mount second PCBA 255 on a second exterior panel of component mounting structure 230. In some other embodiments, the component mounting structure is configured for mounting one or more further PCBAs.

[0134] In some embodiments, the component mounting structure 230 is configured to mount the first PCBA 250 on one side of the component mounting structure 230, and also configured to mount the second PCBA 255 on the opposite side of the component mounting structure 230. When data acquisition unit 110 is assembled, first PCBA 250 may be cable connected to second PCBA 255. The use of component mounting structure 230 to contain power source 240 and mount at least one of: first PCBA 250 or second PCBA 255, helps realise an internal volume efficiency within the data acquisition unit 110. [0135] The component mounting structure 230 may be received in the central chamber. The component mounting structure 230 may be configured to be attached to one or more inside portions of upper part 223. A top portion of component mounting structure 230 may include a recess for allowing cabling for data communications and/or power to/from the satellite modem 290.

[0136] In some other embodiments, component mounting structure 230 may be configured to include, attach, house, and/or mount satellite modem 290, so that satellite modem 290 may be housed within the central chamber of housing 220. Component mounting structure 230 may house the satellite modem 290 in an uppermost compartment of component mounting structure 230. In some other embodiments, component mounting structure 230 may be configured to mount satellite modem 290 on a top exterior surface of component mounting structure 230.

[0137] Data acquisition unit also includes a vibration transducer 260 configured to receive vibrations via the vibrations sensing portion 227 and generate an output signal based on the received vibrations. For example, the output signal generated from the vibration transducer is an analogue output signal. According to some embodiments, the lower part 226 includes the vibration transducer 260. Vibration transducer 350 may be cable connected to either PCBA 250 or PCBA 255. This cabling may allow communicative coupling to a processor and/or analogue to digital converter. The cabling may be insulated to reduce the internal noise of the data acquisition unit 110. In some embodiments, the cabling is between about 10 to 30 cm in length. In some embodiments, another cabling is between about 15 to 20 cm in length. The short length of cabling and/or insulated cabling may reduce the internal noise of the data acquisition unit 110 and improve quality of measurements. According to some embodiments, a lower portion/side/face of component mounting structure 230 includes a recess for allowing cabling to/from vibration transducer 260 to other components of data acquisition unit 110, such as first PCBA 250 and/or second PCBA 255. The recess for allowing cabling to/from vibration transducer 260 may also allow a portion of vibration transducer 260 to be located in component mounting structure 230 and/or within the recess.

[0138] Vibration transducer 260 may be or include a single geophone. Vibration transducer

260 may be arranged to act as a vertical axis geophone element. The geophone may measure vibrations between about 0.1 to 7 Hz. The geophone may have a natural frequency between about 1 to 10 Hz. The geophone may have a natural frequency between about 1 to 3 Hz, 1 to 5 Hz, or 2 to 8 Hz, for example. The geophone may have a natural frequency of about 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, or 10 Hz, for example. In particular, the geophone may be selected to have a natural frequency of about 2 Hz. The geophone may have a natural frequency less than 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, or 10 Hz, for example.

[0139] The geophone may have a sensitivity of about 100 to 300 or 100 to 750 V/m/s, for example. Sensitivity of the geophone may be the intrinsic open circuit voltage sensitivity. In various embodiments, the geophone may have a sensitivity of about 180 to 260 V/m/s, 200 to 280 V/m/s, or 240 to 300 V/m/s, for example. In various embodiments, the geophone may have a sensitivity of about 300 to 400 V/m/s, 400 to 500 V/m/s, or 500 to 650 V/m/s, for example. In various embodiments, the geophone may have a sensitivity of about 120, 140, 160, 180, 200, 220, 240, 260, 280, or 300 V/m/s, for example. In various embodiments, the geophone may have a sensitivity of about 320, 350, 400, 450, 500, 550, 600, 650, 700, or 750 V/m/s, for example. In various embodiments, the geophone may have a sensitivity greater than 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, 320, 350, 400, 450, 500, 550, 600, 650, 700, or 750 V/m/s, for example. For example, the geophone may have a sensitivity greater than 250 V/m/s and a natural frequency less than 2.25 Hz. In another example, the geophone may have a sensitivity greater than 200 V/m/s and a natural frequency less than 3 Hz. In another example, the geophone may have a sensitivity of about 260 V/m/s and a natural frequency of about 2 Hz. In another example, the geophone may have a sensitivity greater than 550 V/m/s and a natural frequency less than 1.25 Hz. In another example, the geophone may have a sensitivity of about 650 V/m/s and a natural frequency of about 1 Hz. The geophone may be a high-sensitivity geophone, such as a ST-2A geophone available from Seis Tech, for example.

[0140] Data acquisition unit 110 can acquire seismic data for ambient noise tomography without the use of active seismic sources and/or stimulated responses. Vibration transducer 260 may be suitable for acquiring low frequency vibrations under 5 Hz. This combination of high sensitivity and low natural frequency allows the vibration sensing module 350 to detect vibrations of a lower frequency than an element of 10 or even 5 Hz. More specifically, the vibration transducer 260 has a higher response gain in the low frequency range of 0.05 to 3 Hz. More traditional nodes with a lower sensitivity and natural frequency at 5 or 10 Hz are more suitable for active seismic methods. The geophone may be configured for measuring Rayleigh waves. In some embodiments, vibration transducer 260 may comprise three geophones measuring three perpendicular axes. Accordingly, the geophone may be a single tri-axial geophone unit, where such a unit is available. The three geophones or tri-axial geophone unit may be configured for measuring Love waves, for example. Each of the geophones/tri-axial geophone unit may have the same and/or similar sensitivity and natural frequency parameters as described above.

[0141] Data acquisition unit 110 may include a light emitting diode (LED) indicator Til. LED indicator 272 may illuminate, dim, and/or turn off to indicate at least one of: boot-up sequence, connection to peripherals, the modem 290 detecting a satellite 130, an alignment of the data acquisition unit 110 is within a suitable threshold for operational orientation based on data from the accelerometer, or warnings concerning battery level or electronics temperature, for example. LED indicator 272 may illuminate different colours such as green, amber, or red, for example.

[0142] Data acquisition unit 110 may include a level indicator 270. Level indicator 270 may be a spirit or bubble level indicator. Level indicator 270 may be a bulls-eye indicator. Level indicator 270 may assist an operator with orienting the data acquisition unit 110 when deploying or physically manipulating the device, particularly for the alignment of vibration transducer 260 with a local gravity vector. Level indicator 270 may be on the top surface of upper part 223, or another surface of data acquisition unit 110 that may be visible when the data acquisition unit 110 is embedded in the ground, for example.

[0143] Data acquisition unit 110 may include a charge port 274. Upper part 223 may include the charge port 274. Charge port 274 may be referred to as charging port 274. Charge port 274 may be connected or connectable to power source 240. External power sources may connect to charge port 274 in order to charge power source 240. In some other embodiments, data acquisition unit may include a push button 274. Push button 274 may be a button electrically connected to PCBAs 250 and/or 255 to power cycle the electronic components of the data acquisition unit 110, such as a processor. [0144] Data acquisition unit 110 may include a debugging port 276. Upper part 223 may include the debugging port 276. Debugging port 276 may be a serial communications port 276. Debugging port 276 may be communicatively coupled to one or more components on first PCBA 250 and/or second PCBA 255. Debugging port 276 may be used to allow an operator to connect an external computing device to data acquisition unit 110 to extract data, perform firmware updates, and/or perform remote debugging, for example.

[0145] Data acquisition unit 110 may include a charge port 278. Upper part 223 may include the charge port 278. Charge port 278 may be a 2 mm power socket, for example. Charge port 278 may be connected or connectable to at least one of: one or more components on first PCBA 250, one or more components on second PCBA 255, or power source 240. External power sources may connect to charge port 278 in order to charge at least one of: one or more components on first PCBA 250, one or more components on second PCBA 255, or power source 240.

[0146] Further examples of data acquisition units are described in more detail in PCT patent specification WO 2023/164738 Al, and Australian patent application 2024901363, which this present specification incorporates entirely by reference.

[0147] Figure 3 shows an example in schematic form of tomography module 154. As shown in figure 3, module 154 may include one or more components, for example model generation engine 300, model validation module 305, operational status monitor 310, data validation module 315, and/or data correction module 320.

[0148] Model generation engine 300 is configured to generate at least one geophysical model of a sub-ground region in a region of interest. Examples of models generated by model generation engine 300 are described below with reference to figures 9A, 9B, 9C, and 10.

[0149] Model validation module 305 may be connected to model generation engine 300, so as to facilitate bi-directional data communication. As a geophysical model is being generated by model generation engine 300, model validation module 305 performs monitoring of the geophysical model to determine whether or not at least one data criterion is met. [0150] The monitoring performed by model validation module 305 may include assessment of the geophysical model against one or more data criteria during the process of generating the geophysical model. Data acquisition units 110 are switchable between a low-power standby mode and a sensing mode. Model generation engine 300 performs model generation while data acquisition units 110 are in sensing mode and the units 110 are acquiring sensor data, such as sensor measurement data, which is then transmitted to tomography module 154.

[0151] At least one of the criteria assessed by model validation module 305 may function as a stop criterion. On satisfaction of a stop criterion, server system 150 transmits a sensing termination command, which may be referred to as a sleep command, to one or more of the data acquisition unit(s) 110. This process is further described below with reference to figure 6. The data acquisition units 110, on receiving the sleep command, are placed into a low-power standby mode, in which sensor measurement data is not transmitted via communication componentry such as that described above with reference to figure 1. In an embodiment, the sensing termination command causes each of the data acquisition units 110 to enter a low- power standby mode.

[0152] Model validation module 305 may, for example, calculate a signal to noise ratio in the received sensor measurement data. The calculated ratio is then measured against a threshold ratio. If the calculated ratio is below a threshold ratio, model validation module 305 may make a determination that the sensor measurement data is of low quality.

[0153] Model validation module 305 may, for example, calculate a spatial resolution of the geophysical model. Where the geophysical model is partially generated, a spatial resolution of the partially generated geophysical model may be calculated. The calculated spatial resolution may be measured against a threshold resolution for at least part of a model volume of the sub-ground region. If the calculated spatial resolution is below the threshold resolution, then model validation module 305 may make a determination that the sensor measurement data is of low quality.

[0154] In the event of a determination that the sensor measurement data is of low quality, at least one stop criterion is determined to be satisfied. Server system 150 may then transmit a sensing termination command to one or more of the data acquisition units 110. The data acquisition units 110 may then be manually adjusted, or otherwise redeployed in an attempt to improve sensor measurement data quality.

[0155] Operational status monitor 310 may receive sensor data in the form of operational status data associated to one or more of the data acquisition units 110. As described below with reference to figure 4, the data acquisition units 110 may transmit a data acquisition unit identifier on successful completion of a boot-up sequence. The unit identifier may include operational status data such as data acquisition unit serial number, location data, tilt data, battery voltage, and internal diagnostics. Alternatively, or additionally, the data acquisition units 110 may transmit operational status data such as location data, orientation data, battery level, electronics temperature data, and/or operational fault data.

[0156] Data validation module 315 may be configured to check sensor measurement data received by server system 150. Data validation module 315 may make a determination that the sensor measurement data is valid, and passes the validated sensor measurement data to model generation engine 300. Data validation module 315 may alternatively make a determination that the sensor measurement data is not suitable for model generation. Some examples of criteria on which data validation module 315 may make this determination are set out below.

[0157] Data validation module 315 may alternatively make a determination that at least some of the sensor measurement data requires some correction. For example, one or more data acquisition units 110 may be exhibiting a tilt or other suboptimal orientation. The data acquisition unit(s) 110 may otherwise be functioning normally.

[0158] In such cases, data validation module 315 may determine that, instead of providing justification for the satisfaction of a stop criterion, the received data simply needs correction. Data validation module 315 is in communication with a data correction module 320. Data correction module 320 performs data correction on the sensor measurement data then passes the corrected sensor measurement data to model generation engine 300. [0159] Figure 4 shows an example method 400 for initiating a data acquisition unit 110.

Data acquisition unit 110 is typically deployed or placed in field by an operator. The operator switches 405 on data acquisition unit 110, for example by activating push button 274 to power cycle the electronic components of data acquisition unit 110. Data acquisition units 110 may be configured to enter low-power standby mode by default when first activated in the field after deployment.

[0160] Once data acquisition unit 110 is switched on in the field, unit 110 executes 410 a boot-up sequence in which all peripherals are checked to ensure that they are working and/or responding as required. The boot-up sequence may include, for example, transmitting a request for telemetry data to the satellite constellation 135 via communication links 118.

[0161] The boot-up sequence 410 may include a request to register some or all of the data acquisition units 110 as part of a data acquisition array 115. The registration may be performed by the server system 150 as part of a process of setting up a data acquisition array 115.

[0162] If 415 the boot-up sequence is successfully completed, data acquisition unit 110 transmits 420 a data acquisition unit identifier. The identifier may include a unique data packet containing one or more of the following: data acquisition unit serial number, location data, tilt data, battery voltage, and internal diagnostics.

[0163] If the boot-up sequence is successfully completed, the data acquisition unit 110 may additionally or alternatively transmit an indication that the data acquisition unit 110 is in low- power standby mode.

[0164] The boot-up sequence 410 for a data acquisition unit 110 may be performed before or after deployment of the data acquisition unit 110 in the field. For example, a data acquisition unit 110 may be registered as part of a data acquisition array 115 before or after deployment of the data acquisition unit 110 in the field.

[0165] As described above, data acquisition unit 110 may measure seismic vibration in a ground region near where it is deployed. A geophone element may be used to generate electrical signals proportional to the vibrational velocity induced in the data acquisition unit 110. Data acquisition unit 110 may sample its single geophone every 50 milliseconds (20 Hz), for example.

[0166] Data acquisition unit 110 may be configured to be placed in a sensing mode in which the geophone element is actively being sampled. Data acquisition unit 110 may also be placed in a standby mode to conserve operation of power source 240, more specifically batteries and/or storage cells.

[0167] As indicated at 425, data acquisition unit 110 may be placed in low-power standby mode to conserve power. In standby mode the data acquisition unit 110 does not undertake passive seismic sensing, and does not transmit sensor measurement data. Data acquisition units 110 may occasionally send a heartbeat or battery level.

[0168] Placing a data acquisition unit 110 in low-power standby mode may be performed by a field operator manually operating a control on the data acquisition unit 110. Alternatively, or additionally, the data acquisition unit 110 may receive a request from the server system 150 to place the data acquisition unit 110 in low-power standby mode.

[0169] Figures 5 and 6 show methods for controlling data acquisition units 110. Method 500 is typically performed by server system 150. Method 600 is typically performed by data acquisition unit 110.

[0170] Server system 150 transmits 505 a wake up command, also referred to as a sensing initiation command, to one or more data acquisition units 110 within a data acquisition array 115. Transmitting 505 of the sensing initiation command to a data acquisition unit 110 would usually be performed after deployment of the data acquisition unit 110.

[0171] Server system 150 may transmit a plurality of wake up command messages. The plurality of messages may be addressed to respective data acquisition units 110. Where server system 150 transmits a plurality of messages, the messages may be queued for transmission to different data acquisition units 110. [0172] The wake up command may be initiated on client computing device 160 connected to server system 150 by communication link 157. For example, the wake up command, or a request to construct a wake up command, may be transmitted from client computing device 160 to server system 150. The wake up command may be transmitted to ground station(s) 140 via communications link 148.

[0173] The wake up command may be transmitted from ground station(s) 140 to satellite constellation 135 via communication link 138, and then to data acquisition unit(s) 110 via communication link 118.

[0174] The data acquisition units 110 receive 605 the wake up command transmitted from the server system 150 via ground station(s) 140 and satell ite(s) 130.

[0175] On receiving a sensing initiation command, data acquisition unit 110 switches 610 to sensing mode. Data acquisition unit 110 acquires and/or transmits sensor data. One example of sensor data includes sensor measurement data acquired by data acquisition unit 110 while in sensing mode. Geophone element 260 of data acquisition unit 110 operates to generate electrical signals proportional to the vibrational velocity induced in the data acquisition unit 110. Data acquisition unit 110 acquires 615 sensor measurement data by measuring seismic vibration in a ground region near where it is deployed.

[0176] Transmitting 505 the sensing initiation command to a data acquisition unit 110 would usually be performed after data acquisition unit 110 has been registered as part of a data acquisition array 115. Furthermore, transmitting 505 the sensing initiation command to a data acquisition unit 110 would usually be performed after receiving an indication from the data acquisition unit 110 that the data acquisition unit 110 is in low-power standby mode.

[0177] Data acquisition units 110 transmit 620 respective sensor measurement data to the server system 150. The sensor measurement data may include, for example, 1-bit normalised data.

[0178] The sensor measurement data may be transmitted, for example, over communication link(s) 118 to satel lite(s) 130. The sensor measurement data may then be transmitted to ground station(s) 140 via communication link 138 and then to server system 150 via communication link 148.

[0179] The server system 150 receives 510 the sensor measurement data generated by, and transmitted from, the data acquisition units 110. Server system 150 may generate, for example, a geophysical model of a sub-ground region in the region of interest based on the received sensor measurement data.

[0180] Server system 150 may receive 510 the sensor measurement data transmitted from the data acquisition units 110 over several days. For example, data acquisition units 110 may transmit data over a period between about 2 days and about 12 days which is received by the server system 150 over this period. Under good conditions, model generation engine 300 could be expected to generate a suitable model after about four days of operation of data acquisition units 110. Under bad geological conditions, for example sand, model generation could take 6 days. Under better geological conditions, model generation could take as little as 2 days of operation of data acquisition units 110.

[0181] The server system 150 checks 515 for satisfaction of one or more stop criteria. One example of a stop criterion is a determination that a survey is complete. If it is determined, for example, that a generated geophysical model is physically real and of adequate quality, there is no need to receive more sensor measurement data from the data acquisition units 110. This may be expressed as a model spatial resolution criteria of at least part of a model volume of the sub-ground region.

[0182] There are other situations where a survey may be determined to be complete. For example, as the geophysical model is being generated from the sensor measurement data, calculated values of signal to noise ratio will vary. On determining that a rate of change of calculated signal to noise ratio is below a threshold, it may be determined that the survey is complete.

[0183] A survey may be determined to be complete based on a comparison with a previously generated geophysical model. In some situations, a generated geophysical model may be found to closely match a baseline model previously generated for the same region. On detecting such a match, it may be determined that the survey is complete.

[0184] On satisfaction of this stop criterion, server system 150 transmits 520 a sensing determination command, also referred to as a sleep command, to the data acquisition unit(s) 110. Once again, the sleep command may be transmitted via ground station(s) 140 and satellite(s) 130 to data acquisition unit(s) 110.

[0185] Server system 150 may transmit a plurality of sleep command messages. The plurality of messages may be addressed to respective data acquisition units 110. Where server system 150 transmits a plurality of messages, the messages may be queued for transmission to different data acquisition units 110.

[0186] On receiving 625 a sleep command from the server system 150 via ground station(s) 140 and satellite(s) 130, the data acquisition unit 110 switches 630 to standby mode. While in standby mode, the geophone element of data acquisition unit 110 does not operate to generate electrical signals proportional to the vibrational velocity induced in the data acquisition unit 110.

[0187] Another example of a stop criterion is a determination that a time limit has been reached. For example, where model generation engine 300 has been receiving data from acquisition units 110 for a threshold duration, and has still not generated a satisfactory model, then this stop criterion would be satisfied. In this example, server system 150 checks for either generation of a satisfactory model, or reaching a threshold time duration, whichever occurs first. The threshold time duration may comprise a time period of operation of the data acquisition units within the range 2 days to 6 days. One example threshold value is 4 days.

[0188] Another example of a stop criterion relates to a threshold number or proportion of data acquisition units 110 within data acquisition array 115 that are operating correctly. Operational status monitor 310 may determine that individual data acquisition units 110 within data acquisition array 115 are not operating correctly to transmit data due to battery exhaustion and/or some other operation fault. In such cases, server system 150 may check a number of data acquisition units 110 that are detected to be operating against a minimum threshold of data acquisition units that are required to be operating to enable model generation engine 300 to generate a satisfactory model. The minimum threshold may comprise a number, percentage, or proportion of data acquisition units 110 within a data acquisition array 115 that are operating correctly. The minimum threshold may be selected for example from the range 25%-50%.

[0189] Data acquisition units 110 may transmit 620 sensor data in the form of sensor performance data. Such sensor performance data may include power consumption of one or more of the data acquisition units 110. This sensor performance data is received 510 and checked 515 against one or more stop criteria. A data acquisition unit 100 may be determined to be anomalous if the unit is observed to deviate from normal or expected operation. A data acquisition unit 100 may be determined to be degraded if sensor performance is suboptimal or deficient.

[0190] The data acquisition units 110 may have, for example, respective normal power consumption ranges under different operating modes. As described above, a data acquisition unit may have a normal (low) power consumption range of 0.15 to 0.20 W while in standby mode, and a normal (high) power consumption range of 7.0 to 7.5 W while in active sensing node. The low power consumption range may be less than 1 W, for example, while the high power consumption range may be more than 1 or more than 5 W, for example. The low power consumption range may be an order of magnitude lower than the high power consumption range, for example.

[0191] Power consumption of a data acquisition unit 110 that is known to be in standby mode may be observed to be outside a normal low power consumption range of, for example, 0.15 to 0.20 W. Power consumption of a data acquisition unit 110 that is known to be in active sensing mode may be observed to be outside a normal high power consumption range of, for example, 7.0 to 7.5 W. In such cases, the data acquisition unit 110 in the active sensing mode may be determined as degraded on determining that a power consumption of the data acquisition unit 110 is below a normal power consumption range, is above a normal power consumption range, or is otherwise outside a normal power consumption range. Examples of causes of abnormally high power consumption include a short circuit, overheating, or a stuck process associated with data transmission. [0192] Power consumption of a data acquisition unit 110 over time may be observed to reduce or increase at a rate that is above a threshold rate of change. A sudden change, such as an increase or drop in the rate of change, in power consumption may indicate some of the components of data acquisition unit 110 may have stopped functioning. In such cases, the data acquisition unit 110 may be determined as degraded on observing a change, for example sudden drop or sudden increase, in power consumption of the data acquisition unit 110 that is above a threshold rate of change.

[0193] Sensor performance data may include software uptime data associated to one or more of the data acquisition units 110. Software uptime may represent, for example, an amount of time software controlling the data acquisition units 110 is operational without interruption. High uptime in relation to a data acquisition unit 110 may mean that the data acquisition unit 110 is reliable and consistently available for communication. High downtime on the other hand may mean that the data acquisition unit 110 is unreliable due to frequent crashes or failures. This software uptime data is received 510 and checked 515 against one or more stop criteria. The data acquisition units 110 may have, for example, respective expected software uptime ranges.

[0194] A data acquisition unit 110 may be subject to frequent unexpected hardware or software resets which may suggest software crashes or power instability. Such a data acquisition unit 110 may be determined as degraded on determining that a software uptime is below an expected software uptime range.

[0195] A data acquisition unit 110 may be subject to unusually long uptime without expected reboots, which may suggest missed updates, stuck processes, or logging failures. Such a data acquisition unit 110 may be determined as degraded on determining that a software uptime is above an expected software uptime range.

[0196] Sensor performance data may include hardware performance data associated to one or more of the data acquisition units 110. In an embodiment, regular checks of hardware are conducted on the data acquisition units 110. Results of the hardware checks include hardware performance data. In some cases, a data acquisition unit 110 may be determined as degraded based on hardware performance data resulting from the hardware checks. [0197] For example, the hardware performance data may indicate a malfunction in one or more hardware components of a data acquisition unit 110. The unit 110 may be determined as degraded on detecting a malfunction in at least one hardware component of the data acquisition unit 110. Examples of hardware malfunctions include a sensor malfunction, excessive battery degradation, storage device errors, and/or communication failures.

[0198] Sensor performance data may include current draw associated to one or more of the data acquisition units 110. Current draw on certain lines may be received 510 and checked 515 against one or more stop criteria. The data acquisition units 110 may have, for example, respective normal current draw ranges.

[0199] One or more components of a data acquisition unit 110, for example the sensor, may be exhibiting no current draw which may suggest a power supply failure, cable disconnection, or internal circuit fault. Component(s) of a data acquisition unit 110 may be exhibiting a constant current draw at a low value which may indicate a short circuit, component failure, or firmware crash. Such a data acquisition unit 110 may be determined as degraded on determining that a current draw is below a normal current draw range.

[0200] Component(s) of a data acquisition unit 110 may be exhibiting a constant current draw at a high value which may indicate a short circuit, component failure, or firmware crash. Such a data acquisition unit 110 may be determined as degraded on determining that a current draw is above a normal current draw range.

[0201] A data acquisition unit 110 may be determined as degraded on determining that a current draw of component(s) of the data acquisition unit is/are displaying an abnormal current pattern. One example of an abnormal current pattern is a data acquisition unit 110 for which one or more components show sudden spikes or drops. This may suggest intermittent connections, power instability, or environmental interference. Another example of an abnormal current pattern is a data acquisition unit 110 for which one or more components show unusual current patterns compared to other data acquisition units. For example, a degraded data acquisition unit may consistently draw significantly more or less current than others under similar conditions. [0202] Sensor performance data may include an operational state of at least one peripheral device associated to one or more of the data acquisition units 110. One example of a peripheral device is a GPS module. Other examples of peripherals include components that are mounted on mounting structure 230 of data acquisition unit 110 of figure 1, for example, or otherwise removably coupled to a component of the data acquisition unit 110. The peripherals may be internal or external to data acquisition unit 110. An operational state of the at least one peripheral device may be received 510 and checked 515 against one or more stop criteria.

[0203] A data acquisition unit 110 may be determined as degraded on determining that an operational state of one or more peripheral devices associated or coupled to the data acquisition unit is an abnormal operational state. One example of an abnormal operational state is a peripheral device that displays communication failures, such as failure to receive acknowledgements or data from a peripheral device, continuous attempts to reinitialise a peripheral, and/or timeouts during communication.

[0204] Alternatively, or additionally, the data acquisition units 110 may transmit sensor data in the form of operational status data such as location data, orientation data, battery level, electronics temperature data, and/or operational fault data.

[0205] Another example of a stop criteria is the detection of low battery level among some or all of the data acquisition units 110. Data acquisition units 110 may transmit a battery level indicating a battery level associated to respective data acquisition units 110. From this battery level, a battery capacity may be determined for some or all data acquisition units 110 within data acquisition array 115. For example, it may be determined that model generation engine 300 will require data acquisition units 110 to be operating for four days, and it is determined that a minimum threshold of data acquisition units 110 have battery capacity to operate for only three days. In such cases, server system 150 may determine satisfaction of a stop criterion.

[0206] Another example of a stop criteria is the determination of poor diagnostics from the data acquisition units 110. As described above, model validation module 305 may calculate a signal to noise (SNR) ratio that is measured against a threshold ratio. If the calculated ratio is below a threshold ratio, model validation module 305 may make a determination for an individual data acquisition unit 110 that the sensor measurement data associated to that data acquisition unit 110 is of low quality.

[0207] Model validation module 305 may calculate a cross-correlation SNR value that is representative of at least some data acquisition units 110 within a data acquisition array 115. The cross-correlation SNR value may comprise, for example, a median signal to noise ratio of data acquisition units 110 within a data acquisition array 115. Alternatively or additionally, the cross-correlation SNR value may comprise an average signal to noise ratio of data acquisition units 110 within a data acquisition array 115.

[0208] Model validation module 305 may compare the calculated cross-correlation SNR value against a threshold. If the cross-correlation SNR value is below the threshold, the model validation module 305 may make a determination for a data acquisition array 115 that the sensor measurement data associated to that data acquisition array 115 is of low quality. In such cases, server system 150 may determine satisfaction of a stop criterion.

[0209] In some cases, a stop criterion may be satisfied for some but not all data acquisition units 110 within a data acquisition array 115. For example, operational status monitor 310 may determine that one or more data acquisition units 110 is degraded, or that deviates from a normal operation, based on the sensor performance data and/or operational status data received from data acquisition units 110. Operational status monitor 310 may otherwise detect bad sensor measurement data, associated to one or more data acquisition units 110 within a data acquisition array 115.

[0210] Operational status monitor 310 may also detect that there are insufficient data acquisition units 110 operating to generate a satisfactory model.

[0211] In such cases, a sensing termination or sleep command may be transmitted to selected data acquisition units 110 within the data acquisition array 115, for example those data acquisition units 110 that are degraded, or otherwise not transmitting sensor measurement data from which a satisfactory model may be generated. The remaining data acquisition units 110 within the data acquisition array 115 may continue to transmit sensor measurement data from which a model may be generated.

[0212] After the sensing termination command has been transmitted 520 by the server system 150, and received 625 by the data acquisition units 110, the data acquisition units 110 are placed in standby mode. The data acquisition units 110 may then be redeployed in a redeployed space array. The data acquisition units 110, once placed in the redeployed space array, may operate to perform ambient noise tomography in a different region of interest.

[0213] The data acquisition units 110 may, for example, transmit data continuously until they receive the sensing termination command that causes the data acquisition units 110 to stop seismic sensing. Similarly, server system 150 may receive the transmitted data continuously until the sensing termination command causes the data acquisition units 110 to stop seismic sensing.

[0214] Transmitting 520 the sensing termination command to the data acquisition units 110 therefore has the potential to conserve battery life of the data acquisition units 110. While the data acquisition units 110 are in standby mode, they can be redeployed without significant use of their batteries. This means that redeployment may be performed without charging the batteries of at least some of the data acquisition units 110.

[0215] Once the data acquisition units 110 are redeployed, they may follow method 400 for initiating the data acquisition units 110. The operator switches 405 on data acquisition unit 110 if not already powered up, for example by activating push button 274 to power cycle the electronic components of data acquisition unit 110. Some or all of method steps of method 400 may then be executed.

[0216] Once the redeployed data acquisition units 110 have been initiated, some or all of the method steps of figures 500 and 600 may be executed. For example, the server system 150 may transmit 505 a further sensing initiation command to cause some or all of the redeployed array of data acquisition units 110 to begin passive sensing of seismic vibrations to generate further sensor measurement data. The further sensing initiation command may be addressed to all data acquisition data units 110 within the data acquisition array 115, a selection of data acquisition units 110 within the data acquisition array 115. If the data acquisition units 110 are redeployed to a different region of interest, the sensor measurement data transmitted by the data acquisition units 110 will be associated to the different region of interest.

[0217] By following the steps set out in figures 500 and 600, the sensor measurement data from the redeployed data acquisition units 110 enable tomography module 154 to generate a further geophysical model of a sub-ground region in the different region of interest. The further geophysical model may be based on the received further sensor measurement data.

[0218] On satisfaction 515 of at least one stop criteria, server system 150 transmits 520 a further sensing termination command to the data acquisition units 110 in the redeployed array to cause the data acquisition units to stop passive seismic sensing. The further sensing termination commands may be transmitted simultaneously or queued for transmission.

[0219] Figure 7 shows an example of a data packet 700 that may be used to transmit sensor data from a data acquisition unit 110 to one or more of the satellites 130 of satellite constellation 135 of figure 1. Data packet 700 contains a header 705 and a body 710 or message. Header 705 may include a timestamp and message size.

[0220] While data acquisition unit 110 is in an active sensing mode, body 710 may include sensor measurement data 720. Sensor measurement data 720 may be pre-processed before transmittal in data packet 700. Sensor measurement data 720 may be compressed before transmittal in data packet 700. While data acquisition unit 110 is not in an active sensing mode, body 710 may omit sensor measurement data 720.

[0221] Body 710 of data packet 700 may include diagnostic information such as sensor performance data 730 and/or operational status data 740. Examples of sensor performance data 730 and operational status data 740 are set out above.

[0222] Figure 8 shows an example of a data packet 800 that may be used to send commands and/or reconfiguration details to a data acquisition unit 110, or group of data acquisition units. Data packet 800 contains a header 805 and a body 810 or message. Header may include a timestamp and message size.

[0223] Header 805 may include a command identifier to indicate to the data acquisition unit 110 how information contained in body 810 would be used. For example, for some command identifier types, body 810 may include reconfiguration details 820 associated to a data acquisition unit 110 to which data packet 800 is addressed. For other command identifier types, reconfiguration details 820 may be omitted, particular where the command identifier causes a data acquisition unit 110 to placed in sleep mode/low power mode.

[0224] In an embodiment, the command identifier comprises a one-byte number that is enumerated to cover the range of specific individual commands that are able to be interpreted by data acquisition unit 110.

[0225] In an embodiment, body 810 contains a sequence of bytes representing values that could be used to reconfigure on-board parameters. It is envisaged that the contents of body 810 follow a byte structure order that allocates a first sequence of bytes to be a first parameter and a second sequence of bytes to be a second parameter. Decimals and larger numbers may typically require three or four bytes.

[0226] As mentioned above, data packet 800 may be used to send commands and/or reconfiguration details to a data acquisition unit 110, or group of data acquisition units. In an embodiment, data packet 800 includes an identifier for a data acquisition unit, multiple identifiers associated to respective data acquisition units, and/or an identifier associated to multiple data acquisition units. Messages may be filtered on receipt by the data acquisition units 110 to ensure that messages are addressed to the correct data acquisition unit(s) 110.

[0227] Data packet 800 may include further data contained for example in data block 830 and/or data block 840.

[0228] Figures 9A, 9B, 9C, and 10 show examples of geophysical models of a sub-ground region in the region of interest. These models may be generated, for example, by tomography module 154 of server system 150, based on sensor measurement data received from data acquisition units 110.

[0229] The models may include sub-surface imaging obtained through ambient noise tomography processing. The sub-surface imaging is based on seismic data acquired by data acquisition unit 110, for ambient noise tomography processing by server 150, without the use of active seismic sources and/or stimulated responses. The sub-surface imaging may be based on seismic data acquired by a plurality of data acquisition units 110 of data acquisition array 115, for ambient noise tomography processing by server 150, without use of active seismic sources and/or stimulated responses.

[0230] Sub-surface imaging may be performed by server system 150 upon receiving pre- processed data from one or more data acquisition units 110 of data acquisition array 115. Representations and modelling of this imaging may be viewable on client computing device 160.

[0231] Figure 9A shows a gravity method survey yielding a false positive result. This is in contrast to an ambient noise tomography method of Figure 9B over the same sub-surface yielding a correct determination of anomalies. Figure 9B is an example two-dimensional (2-D) splice of a 3-D model. Use of ambient noise techniques may allow dense bodies (typical sources of iron oxide copper-gold, or lithium, for example) to be identified.

[0232] In some embodiments, the data acquisition units 110 of data acquisition array 115 may be deployed in different configurations. In some embodiments, the survey area for imaging may be dependent upon the boundary defined by a perimeter of data acquisition units 110 of the data acquisition array 115. In some embodiments, the data acquisition units 110 may be deployed in an evenly spaced rectangular formation with the imaging area a perimeter boundary defined by the outside data acquisition units 110. In some other embodiments, the data acquisition units 110 of data acquisition array 115 are not all evenly spaced from one another. In some other embodiments, the data acquisition units 110 of data acquisition array 115 are not deployed in a rectangular formation but another arrangement. [0233] In some embodiments, data acquisition units 110 of data acquisition array 115 may be deployed at an equal or near equal distance from one another. In some embodiments, data acquisition units 110 may be deployed at a distance of about 20 metres to about 2 kilometres. In some embodiments, data acquisition units 110 may be deployed at a distance of about 30 metres to about 100 metres, about 100 metres to about 500 metres, or 500 metres to about 1.5 kilometres, for example. In some embodiments, data acquisition units 110 may be deployed at a distance of about 20 metres, 50 metres, 100 metres, 200 metres, 400 metres, 600 metres, 800 metres, 1 kilometre, 1.2 kilometres, 1.5 kilometres, or about 2 kilometres from one another, for example.

[0234] The spacing of the deployed data acquisition units 110 in data acquisition array 115 may influence the depth of imaging. The depth of imaging may be proportional to the spacing distance of the data acquisition units 110 of data acquisition array 115. In some embodiments, the depth of imaging may be about 5 times the spacing distance between each of the data acquisition units 110 of data acquisition array 115. The greater the spacing distance between data acquisition units 110 of data acquisition array, the greater the depth of the imaging. However, a greater spacing may lead to a decrease In image resolution.

[0235] In some embodiments, an adequate amount of ground-movement data from one or more data acquisition units 110 of data acquisition array 115 may be collected for server system 150 to generate a display of a first ground region on the user interface, and then at least one of the plurality of data acquisition units 110 may be repositioned at surface locations across a second ground region. Then at least one of the plurality of data acquisition units 110 is configured to collect a second amount of ground-movement data for a display of the second ground region before the power source 240 or supply requires recharging or replacing.

[0236] In some embodiments, the second amount of ground-movement data is an adequate amount of data collected for server system 150 to generate a display of the second ground region on the user interface.

[0237] In some embodiments, the data acquisition units 110 are repositioned from the first ground region to the second ground region at least in part by vehicular transport. [0238] In some embodiments, a further one or more data acquisition units 110 are deployed in the first ground region whilst server system 150 is receiving pre-processed ground movement data and/or performing ambient noise tomography and/or generating tomography data and/or generating the display. The server system 150 is then configured to receive and process further pre-processed ground movement data from the further data acquisition units 110 and perform ambient noise tomography and generate tomography data based on both the pre-processed ground movement data and the further pre-processed ground movement data.

[0239] In some embodiments, one or more data acquisition units 110 of data acquisition array 115 in the first ground region are moved to another location within the first ground region whilst sampling is occurring, and the server system 150 is then configured to receive and process the new pre-processed ground movement data from the repositioned data acquisition units 110 and the stagnant data acquisition units 110 and perform ambient noise tomography and generate tomography data from the data sampled from the data acquisition array 115.

[0240] Therefore, some embodiments relate to a method of data acquisition performed by a data acquisition system 100, the data acquisition system 100 including one or more of the data acquisition units 110 according to embodiments of the present disclosure, the method comprising: positioning one or more of the data acquisition units 110 at spaced surface locations across a ground region; and operating each of the one or more data acquisition units 110 to receive vibrations over a plurality of days; wherein the one or more of data acquisition units 110 are operable to generate and send processed data based on vibrations received by the one or more data acquisition units 100 at the spaced surface locations.

[0241] The operating may include continuous operation of the one or more data acquisition units 110 to receive vibrations. The operating may include continuous operation of the one or more data acquisition units 110 to receive vibrations for a period of between 4 and 10 days, wherein a power supply 240 or power source 240 of each of the one or more data acquisition units 110 is contained within the housing 220 of each of the one or more data acquisition units 110 and is configured to supply power for operation of the respective data acquisition unit 110 for more than 10 days. [0242] The data acquisition system 100 includes one or more satellites 130, one or more ground stations 140, and a server system 150, and wherein the one or more data acquisition units 110 are operable to generate and send the processed data, via the one or more satellites 130 and one or more ground stations 140, to a server system 150 for performing computed tomography of the subsurface of the ground region.

[0243] Figure 11 shows an example computer system 1100. In particular embodiments, one or more computer systems 1100 perform one or more steps of one or more methods described or illustrated herein. In particular embodiments, one or more computer systems 1100 provide functionality described or illustrated herein. In particular embodiments, software running on one or more computer systems 1100 performs one or more steps of one or more methods described or illustrated herein or provides functionality described or illustrated herein. Particular embodiments include one or more portions of one or more computer systems 1100. Herein, reference to a computer system may encompass a computing device, and vice versa, where appropriate. Moreover, reference to a computer system may encompass one or more computer systems, where appropriate. The server system 150, tomography module 154, component(s) of tomography module 154, data visualisation module 156, data storage 152, and/or client computing device 160 may incorporate a subset or all of the computing components described with reference to the computer system 1100 to provide the functionality described in this specification.

[0244] This disclosure contemplates any suitable number of computer systems 1100 to implement each of the server system 150, tomography system 154, data visualisation system 156, data storage 152, and/or client computing device 160. Computer system 1100 may be an embedded computer system, a system-on-chip (SOC), a single-board computer system (SBC) (such as, for example, a computer-on-module (COM) or system-on-module (SOM)), a desktop computer system, a laptop or notebook computer system, an interactive kiosk, a mainframe, a mesh of computer systems, a mobile telephone, a personal digital assistant (PDA), a server, a tablet computer system, or a combination of two or more of these. Where appropriate, computer system 1100 may include one or more computer systems 1100; be unitary or distributed; span multiple locations; span multiple machines; span multiple data centres; or reside in a cloud, which may include one or more cloud components in one or more networks. Where appropriate, one or more computer systems 1100 may perform without substantial spatial or temporal limitation one or more steps of one or more methods described or illustrated herein. As an example, and not by way of limitation, one or more computer systems 1100 may perform in real-time or in batch mode one or more steps of one or more methods described or illustrated herein. One or more computer systems 1100 may perform at different times or at different locations one or more steps of one or more methods described or illustrated herein, where appropriate.

[0245] In particular embodiments, computer system 1100 includes a processor 1102, memory 1104, storage 1106, an input/output (I/O) interface 1108, a communication interface 1110, and a bus 1112. Although this disclosure describes and illustrates a particular computer system having a particular number of particular components in a particular arrangement, this disclosure contemplates any suitable computer system having any suitable number of any suitable components in any suitable arrangement.

[0246] In particular embodiments, processor 1102 includes hardware for executing instructions, such as those making up a computer program. As an example, and not by way of limitation, to execute instructions, processor 1102 may retrieve (or fetch) the instructions from an internal register, an internal cache, memory 1104, or storage 1106; decode and execute them; and then write one or more results to an internal register, an internal cache, memory 1104, or storage 1106. In particular embodiments, processor 1102 may include one or more internal caches for data, instructions, or addresses. This disclosure contemplates processor 1102 including any suitable number of any suitable internal caches, where appropriate. As an example, and not by way of limitation, processor 1102 may include one or more instruction caches, one or more data caches, and one or more translation lookaside buffers (TLBs). Instructions in the instruction caches may be copies of instructions in memory 1104 or storage 1106, and the instruction caches may speed up retrieval of those instructions by processor 1102. Data in the data caches may be copies of data in memory 1104 or storage 1106 for instructions executing at processor 1102 to operate on; the results of previous instructions executed at processor 1102 for access by subsequent instructions executing at processor 1102 or for writing to memory 1104 or storage 1106; or other suitable data. The data caches may speed up read or write operations by processor 1102. The TLBs may speed up virtual-address translation for processor 1102. In particular embodiments, processor 1102 includes one or more internal registers for data, instructions, or addresses. This disclosure contemplates processor 1102 including any suitable number of any suitable internal registers, where appropriate. Where appropriate, processor 1102 may include one or more arithmetic logic units (ALUs); be a multi-core processor; or include one or more processors 1102. Although this disclosure describes and illustrates a particular processor, this disclosure contemplates any suitable processor.

[0247] In particular embodiments, memory 1104 includes main memory for storing instructions for processor 1102 to execute or data for processor 1102 to operate on. As an example, and not by way of limitation, computer system 1100 may load instructions from storage 1106 or another source (such as, for example, another computer system 1100) to memory 1104. Processor 1102 may then load the instructions from memory 1104 to an internal register or internal cache. To execute the instructions, processor 1102 may retrieve the instructions from the internal register or internal cache and decode them. During or after execution of the instructions, processor 1102 may write one or more results (which may be intermediate or final results) to the internal register or internal cache. Processor 1102 may then write one or more of those results to memory 1104. In particular embodiments, processor 1102 executes only instructions in one or more internal registers or internal caches or in memory 1104 (as opposed to storage 1106 or elsewhere) and operates only on data in one or more internal registers or internal caches or in memory 1104 (as opposed to storage 1106 or elsewhere). One or more memory buses (which may each include an address bus and a data bus) may couple processor 1102 to memory 1104. Bus 1112 may include one or more memory buses, as described below. In particular embodiments, one or more memory management units (MMUs) reside between processor 1102 and memory 1104 and facilitate accesses to memory 1104 requested by processor 1102. In particular embodiments, memory 1104 includes random access memory (RAM). This RAM may be volatile memory, where appropriate. Where appropriate, this RAM may be dynamic RAM (DRAM) or static RAM (SRAM). Moreover, where appropriate, this RAM may be single-ported or multi-ported RAM. This disclosure contemplates any suitable RAM. Memory 1104 may include one or more memories 1104, where appropriate. Although this disclosure describes and illustrates particular memory, this disclosure contemplates any suitable memory.

[0248] In particular embodiments, storage 1106 includes mass storage for data or instructions. As an example, and not by way of limitation, storage 1106 may include a hard disk drive (HDD), a floppy disk drive, flash memory, an optical disc, a magneto-optical disc, magnetic tape, or a Universal Serial Bus (USB) drive or a combination of two or more of these. Storage 1106 may include removable or non-removable (or fixed) media, where appropriate. Storage 1106 may be internal or external to computer system 1100, where appropriate. In particular embodiments, storage 1106 is non-volatile, solid-state memory. In particular embodiments, storage 1106 includes read-only memory (ROM). Where appropriate, this ROM may be mask-programmed ROM, programmable ROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM), electrically alterable ROM (EAROM), or flash memory or a combination of two or more of these. This disclosure contemplates mass storage 1106 taking any suitable physical form. Storage 1106 may include one or more storage control units facilitating communication between processor 1102 and storage 1106, where appropriate. Where appropriate, storage 1106 may include one or more storages 1106. Although this disclosure describes and illustrates particular storage, this disclosure contemplates any suitable storage.

[0249] In particular embodiments, I/O interface 1108 includes hardware, software, or both, providing one or more interfaces for communication between computer system 1100 and one or more I/O devices. Computer system 1100 may include one or more of these I/O devices, where appropriate. One or more of these I/O devices may enable communication between a person and computer system 1100. As an example, and not by way of limitation, an I/O device may include a keyboard, keypad, microphone, monitor, mouse, printer, scanner, speaker, still camera, stylus, tablet, touch screen, trackball, video camera, another suitable I/O device or a combination of two or more of these. An I/O device may include one or more sensors. This disclosure contemplates any suitable I/O devices and any suitable I/O interfaces X08 for them. Where appropriate, I/O interface 1108 may include one or more device or software drivers enabling processor 1102 to drive one or more of these I/O devices. I/O interface 1108 may include one or more I/O interfaces 1108, where appropriate. Although this disclosure describes and illustrates a particular I/O interface, this disclosure contemplates any suitable I/O interface.

[0250] In particular embodiments, communication interface 1110 includes hardware, software, or both providing one or more interfaces for communication (such as, for example, packet-based communication) between computer system 1100 and one or more other computer systems 1100 or one or more networks. As an example, and not by way of limitation, communication interface 1110 may include a network interface controller (NIC) or network adapter for communicating with an Ethernet or other wire-based network or a wireless NIC (WNIC) or wireless adapter for communicating with a wireless network, such as a WI-FI network. This disclosure contemplates any suitable network and any suitable communication interface 1110 for it. As an example, and not by way of limitation, computer system 1100 may communicate with an ad hoc network, a personal area network (PAN), a local area network (LAN), a wide area network (WAN), a metropolitan area network (MAN), or one or more portions of the Internet or a combination of two or more of these. One or more portions of one or more of these networks may be wired or wireless. As an example, computer system 1100 may communicate with a wireless PAN (WPAN) (such as, for example, a BLUETOOTH WPAN), a WI-FI network, a WI-MAX network, a cellular telephone network (such as, for example, a Global System for Mobile Communications (GSM) network), or other suitable wireless network or a combination of two or more of these. Computer system 1100 may include any suitable communication interface 1110 for any of these networks, where appropriate. Communication interface 1110 may include one or more communication interfaces 1110, where appropriate. Although this disclosure describes and illustrates a particular communication interface, this disclosure contemplates any suitable communication interface.

[0251] In particular embodiments, bus 1112 includes hardware, software, or both coupling components of computer system 1100 to each other. As an example and not by way of limitation, bus 1112 may include an Accelerated Graphics Port (AGP) or other graphics bus, an Enhanced Industry Standard Architecture (EISA) bus, a front-side bus (FSB), a HYPERTRANSPORT (HT) interconnect, an Industry Standard Architecture (ISA) bus, an INFINIBAND interconnect, a low-pin-count (LPC) bus, a memory bus, a Micro Channel Architecture (MCA) bus, a Peripheral Component Interconnect (PCI) bus, a PCI-Express (PCIe) bus, a serial advanced technology attachment (SATA) bus, a Video Electronics Standards Association local (VLB) bus, or another suitable bus or a combination of two or more of these. Bus 1112 may include one or more buses X12, where appropriate. Although this disclosure describes and illustrates a particular bus, this disclosure contemplates any suitable bus or interconnect. [0252] Herein, a computer-readable non-transitory storage medium or media may include one or more semiconductor-based or other integrated circuits (iCs) (such, as for example, field-programmable gate arrays (FPGAs) or application-specific iCs (ASICs)), hard disk drives (HDDs), hybrid hard drives (HHDs), optical discs, optical disc drives (ODDs), magneto-optical discs, magneto-optical drives, floppy diskettes, floppy disk drives (FDDs), magnetic tapes, solid-state drives (SSDs), RAM -drives, SECURE DIGITAL cards or drives, any other suitable computer-readable non-transitory storage media, or any suitable combination of two or more of these, where appropriate. A computer-readable non-transitory storage medium may be volatile, non-volatile, or a combination of volatile and non-volatile, where appropriate.

[0253] It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

CLAUSES DESCRIBING EMBODIMENTS

1. A method of controlling seismic sensing nodes for ambient noise tomography (ANT), the method including: transmitting a sensing initiation command simultaneously to a plurality of the seismic sensing nodes to cause the seismic sensing nodes to begin passive seismic sensing for ANT, each of the seismic sensing nodes being deployed as part of a spaced array of seismic sensing nodes, the spaced array extending across a region of interest, the seismic sensing nodes having their own respective power supplies, vibration sensors, and communication componentry; receiving sensor data from the seismic sensing nodes while the seismic sensing nodes remain deployed across the region; generating a geophysical model of a sub-ground region in the region of interest based on the received sensor data; and transmitting a sensing termination command simultaneously to the seismic sensing nodes to cause the seismic sensing nodes to stop the passive seismic sensing.

2. The method of clause 1, wherein the receiving includes receiving the sensor data via at least one satellite. 3. The method of clause 1, wherein the receiving includes receiving the sensor data via at least one low earth orbit satellite and/or at least one geostationary satellite.

4. The method of any one of clauses 1 to 3, wherein the transmitting is performed by a server in wireless communication with the seismic sensing nodes via one or more satellites.

5. The method of any one of clauses 1 to 4, wherein the sensing termination command is to cause each of the seismic sensing nodes to enter a low-power standby mode in which passive seismic sensing is not performed by the seismic sensing nodes.

6. The method of any one of clauses 1 to 5, further including, prior to transmitting the sensing initiation command, registering each of the seismic sensing nodes as part of the array and receiving an indication that each seismic sensing node in the array is in low-power standby mode.

7. The method of clause 6, further including, after the registering and prior to transmitting the sensing initiation command, deploying the seismic sensing nodes in the spaced array.

8. The method of any one of clauses 1 to 7, further including monitoring the geophysical model as it is generated to determine whether at least one data criterion is met, wherein the sensing termination command is transmitted in response to determining that the at least one data criterion has been met.

9. The method of clause 8, wherein the at least one criterion includes one or more of: a calculated signal to noise ratio of the sensor data; a calculated cross-correlation signal to noise ratio representative of at least one of the data acquisition units within the spaced array; a model spatial resolution criterion of at least part of a model volume of the sub-ground region; a threshold time duration; a threshold number of data acquisition units that are operating within the spaced array; or a threshold battery capacity among at least one of the data acquisition units within the spaced array.

10. The method of any one of clauses 1 to 9, wherein the receiving includes receiving sensor data over a plurality of days between about 3 days and about 12 days.

11. The method of any one of clauses 1 to 10, wherein the receiving includes receiving the sensor data continuously until the sensing termination command causes the seismic sensing nodes to stop seismic sensing.

12. The method of any one of clauses 1 to 11, wherein the received sensor data is 1-bit normalised data.

13. The method of any one of clauses 1 to 12, wherein the communication componentry includes a wireless modem.

14. The method of clause 13, wherein the wireless modem includes a satellite modem.

15. The method of any one of clauses 1 to 14, further including, after transmitting the sensing termination command, redeploying the seismic sensing nodes in a redeployed spaced array of the seismic sensing nodes to perform ANT in a different region of interest.

16. The method of clause 15, wherein the redeploying is performed without recharging the seismic sensing nodes.

17. The method of clause 15 or clause 16, further including, after the redeploying, transmitting a further sensing initiation command to cause some or all of the redeployed array of seismic sensing nodes to begin passive sensing of seismic vibrations to generate further sensor data in relation to the different region of interest.

18. The method of clause 17, further including: generating a further geophysical model of a sub-ground region in the different region of interest based on the received further sensor data; and transmitting a further sensing termination command simultaneously to the seismic sensing nodes in the redeployed array to cause the seismic sensing nodes to stop the passive seismic sensing.

19. The method of any one of clauses 1 to 18, further including receiving operational status data from each of the seismic sensing nodes, the operational status data including at least one of: node location data; node orientation data; node battery level data; electronics temperature data; or node operational fault data.

20. A system for ambient noise tomography including: processing circuitry; and memory storing program code that, when executed by processing circuity, causes the processing circuity to perform the method of any one of clauses 1 to 19.

21. A system for ambient noise tomography including: a server including processing circuitry and having access to memory; wherein the memory stores program code that, when executed by the processing circuity, causes the processing circuity to: transmit a sensing initiation command simultaneously to a plurality of the seismic sensing nodes to cause the seismic sensing nodes to begin passive seismic sensing for ANT, each of the seismic sensing nodes being deployed as part of a spaced array of seismic sensing nodes, the spaced array extending across a region of interest, the seismic sensing nodes having their own respective power supplies, vibration sensors, and communication componentry; receive sensor data from the seismic sensing nodes while the seismic sensing nodes remain deployed across the region; generate a geophysical model of a sub-ground region in the region of interest based on the received sensor data; and transmit a sensing termination command simultaneously to the seismic sensing nodes to cause the seismic sensing nodes to stop the passive seismic sensing. 22. The system of clause 21 wherein the receiving performed by the processing circuitry includes receiving the sensor data via at least one satellite.

23. The system of clause 21 wherein the receiving performed by the processing circuitry includes receiving the sensor data via at least one low earth orbit satellite and/or at least one geostationary satellite.

24. The system of any one of clauses 21 to 23 wherein the transmitting performed by the processing circuitry is performed in wireless communication with the seismic sensing nodes via one or more satellites.

25. The system of any one of clauses 21 to 24 wherein the sensing termination command is to cause each of the seismic sensing nodes to enter a low-power standby mode in which passive seismic sensing is not performed by the seismic sensing nodes.

26. The system of any one of clauses 21 to 25 wherein the program code further causes the processing circuitry to, prior to the transmission of the sensing initiation command, register each of the seismic sensing nodes as part of the array and receive an indication that each seismic sensing nodes in the array is in low-power standby mode.

27. The system of any one of clauses 21 to 26 wherein the program code further causes the processing circuitry to monitor the geophysical model as it is generated to determine whether at least one data criterion is met, wherein the sensing termination command is transmitted in response to determining that the at least one data criterion has been met.

28. The system of clause 27, wherein the at least one criterion includes one or more of: a calculated signal to noise ratio of the sensor data; a calculated cross-correlation signal to noise ratio representative of at least one of the data acquisition units within the spaced array; a model spatial resolution criterion of at least part of a model volume of the sub-ground region; a threshold time duration; a threshold number of data acquisition units that are operating within the spaced array; or a threshold battery capacity among at least one of the data acquisition units within the spaced array.

29. The system of any one of clauses 21 to 28 wherein the receiving includes receiving sensor data over a plurality of days between about 3 days and about 12 days.

30. The system of any one of clauses 21 to 29 wherein the receiving includes receiving the sensor data continuously until the sensing termination command causes the seismic sensing nodes to stop seismic sensing.

31. The system of any one of clauses 21 to 30 wherein the received sensor data is 1-bit normalised data.

32. The system of any one of clauses 21 to 31, wherein the program code further causes the processing circuitry to, after redeployment of the seismic sensing nodes in a redeployed spaced array of the seismic sensing nodes to perform ANT in a different region of interest, transmit a further sensing initiation command to cause some or all of the redeployed array of seismic sensing nodes to begin passive sensing of seismic vibrations to generate further sensor data in relation to the different region of interest.

33. The system of clause 32, wherein the program code further causes the processing circuitry to: generate a further geophysical model of a sub-ground region in the different region of interest based on received further sensor data; and transmit a further sensing termination command simultaneously to the seismic sensing nodes in the redeployed array to cause the seismic sensing nodes to stop the passive seismic sensing.

34. The system of any one of clauses 21 to 33, wherein the program code further causes the processing circuitry to receive operational status data from each of the seismic sensing nodes, the operation status data including at least one of: node location data; node orientation data; node battery level data; electronics temperature data; or node operational fault data.

35. A method of controlling a plurality of seismic sensing nodes for ambient noise tomography (ANT), at least some of the seismic sensing nodes being deployed as part of a spaced array of seismic sensing nodes, the spaced array extending across a region of interest, wherein the seismic sensing nodes have their own respective power supplies, vibration sensors, and communication componentry, the method including: at least some of the seismic sensing nodes in the spaced array receiving a sensing initiation command simultaneously, to cause the seismic sensing nodes to begin passive seismic sensing for ANT; transmitting sensor data generated from the passive seismic sensing performed by the seismic sensing nodes while the seismic sensing nodes remain deployed across the region, for generation of a geophysical model of a sub-ground region in the region of interest based on the received sensor data; at least some of the seismic sensing nodes in the spaced array receiving a sensing termination command simultaneously, to cause those seismic sensing nodes that are performing the passive seismic sensing to stop the passive seismic sensing.

36. The method of clause 35, wherein the transmitting includes transmitting the sensor data via at least one satellite.

37. The method of clause 35, wherein the transmitting includes transmitting the sensor data via at least one low earth orbit satellite and/or at least one geostationary satellite.

38. The method of any one of clauses 35 to 37, wherein the transmitting is performed in wireless communication with a server via one or more satellites.

39. The method of any one of clauses 35 to 38, wherein the sensing termination command is to cause each of the seismic sensing nodes to enter a low-power standby mode in which passive seismic sensing is not performed by the seismic sensing nodes. 40. The method of any one of clauses 35 to 39, further including, prior to receiving the sensing initiation command, registering each of the seismic sensing nodes as part of the array and transmitting an indication that each seismic sensing node in the array is in low-power standby mode.

41. The method of clause 40, further including, after the registering and prior to receiving the sensing initiation command, deploying the seismic sensing nodes in the spaced array.

42. The method of any one of clauses 35 to 41, further including receiving the sensing termination command in response to a monitoring of the geophysical model as it is generated and determining that at least one data criterion is met.

43. The method of clause 42, wherein the at least one criterion includes one or more of: a calculated signal to noise ratio of the sensor data; a calculated cross-correlation signal to noise ratio representative of at least one of the data acquisition units within the spaced array; a model spatial resolution criterion of at least part of a model volume of the sub-ground region; a threshold time duration; a threshold number of data acquisition units that are operating within the spaced array; or a threshold battery capacity among at least one of the data acquisition units within the spaced array.

44. The method of any one of clauses 35 to 43, wherein the transmitting includes transmitting sensor data over a plurality of days between about 3 days and about 12 days.

45. The method of any one of clauses 35 to 44, wherein the transmitting includes transmitting the sensor data continuously until the received sensing termination command causes the seismic sensing nodes to stop seismic sensing. 46. The method of any one of clauses 35 to 45, wherein the transmitted sensor data is 1-bit normalised data.

47. The method of any one of clauses 35 to 46, wherein the communication componentry includes a wireless modem.

48. The method of clause 47, wherein the wireless modem includes a satellite modem.

49. The method of any one of clauses 35 to 48, further including, after receiving the sensing termination command, redeploying the seismic sensing nodes in a redeployed spaced array of the seismic sensing nodes to perform ANT in a different region of interest.

50. The method of clause 49, wherein the redeploying is performed without recharging the seismic sensing nodes.

51. The method of clause 49 or clause 50, further including, after the redeploying, receiving a further sensing initiation command to cause some or all of the redeployed array of seismic sensing nodes to begin passive sensing of seismic vibrations to generate further sensor data in relation to the different region of interest, for the generation of a further geophysical model of a sub-ground region in the different region of interest based on the further sensor data.

52. The method of clause 51, further including: receiving a further sensing termination command simultaneously at the seismic sensing nodes in the redeployed array to cause the seismic sensing nodes to stop the passive seismic sensing.

53. The method of any one of clauses 35 to 52, further including transmitting operational status data associated to the seismic sensing node(s), the operational status data including at least one of: node location data; node orientation data; node battery level data; electronics temperature data; or node operational fault data. 54. A system for ambient noise tomography including a plurality of seismic sensing nodes for ambient noise tomography (ANT), the seismic sensing nodes having their own respective power supplies, vibration sensors, and communication componentry, the communication componentry configured to perform the method of any one of clauses 35 to 53.

55. A system for ambient noise tomography including: a plurality of seismic sensing nodes for ambient noise tomography (ANT), the seismic sensing nodes having their own respective power supplies, vibration sensors, and communication componentry, at least some of the seismic sensing nodes deployed as part of a spaced array of seismic sensing nodes, the spaced array extending across a region of interest, the communication componentry configured to: receive a sensing initiation command simultaneously, to cause the seismic sensing nodes to begin passive seismic sensing for ANT; transmit sensor data generated from the passive seismic sensing performed by the seismic sensing nodes while the seismic sensing nodes remain deployed across the region, for generation of a geophysical model of a sub-ground region in the region of interest based on the received sensor data; and receive a sensing termination command simultaneously, to cause those seismic sensing nodes that are performing the passive seismic sensing to stop the passive seismic sensing.

56. The system of clause 55 wherein the transmitting includes transmitting the sensor data via at least one satellite.

57. The system of clause 55 wherein the transmitting includes transmitting the sensor data via at least one low earth orbit satellite and/or at least one geostationary satellite.

58. The system of any one of clauses 55 to 57 wherein the transmitting is performed in wireless communication with a server via one or more satellites. 59. The system of any one of clauses 55 to 58 wherein the sensing termination command is to cause each of the seismic sensing nodes to enter a low-power standby mode in which passive seismic sensing is not performed by the seismic sensing nodes.

60. The system of any one of clauses 55 to 59 wherein the communication componentry is configured to, prior to receiving the sensing initiation command, register each of the seismic sensing nodes as part of the array and transmit an indication that each seismic sensing node in the array is in low-power standby mode.

61. The system of any one of clauses 55 to 60 wherein the communication componentry is configured to receive the sensing termination command in response to a monitoring of the geophysical model as it is generated and determining that at least one data criterion is met.

62. The system of clause 61, wherein the at least one criterion includes one or more of: a calculated signal to noise ratio of the sensor data; a calculated cross-correlation signal to noise ratio representative of at least one of the data acquisition units within the spaced array; a model spatial resolution criterion of at least part of a model volume of the sub-ground region; a threshold time duration; a threshold number of data acquisition units that are operating within the spaced array; or a threshold battery capacity among at least one of the data acquisition units within the spaced array.

63. The system of any one of clauses 55 to 60 wherein the transmitting includes transmitting sensor data over a plurality of days between about 3 days and about 12 days.

64. The system of any one of clauses 55 to 63 wherein the transmitting includes transmitting the sensor data continuously until the received sensing termination command causes the seismic sensing nodes to stop seismic sensing. 65. The system of any one of clauses 55 to 64 wherein the transmitted sensor data is 1-bit normalised data.

66. The system of any one of clauses 55 to 65 wherein the communication componentry includes a wireless modem.

67. The system of clause 66 wherein the wireless modem includes a satellite modem.

68. The system of any one of clauses 55 to 67, wherein the communication componentry is configured to, after redeployment of the seismic sensing nodes in a redeployed spaced array of the seismic sensing nodes to perform ANT in a different region of interest, receive a further sensing initiation command to cause some or all of the redeployed array of seismic sensing nodes to begin passive sensing of seismic vibrations to generate further sensor data in relation to the different region of interest, for the generation of a further geophysical model of a subground region in the different region of interest based on the further sensor data.

69. The system of clause 68 wherein the communication componentry is configured to receive a further sensing termination command simultaneously at the seismic sensing nodes in the redeployed array to cause the seismic sensing nodes to stop the passive seismic sensing.

70. The system of any one of clauses 55 to 69, wherein the communication componentry is further configured to transmit operational status data associated to the seismic sensing node(s), the operational status data including at least one of: node location data; node orientation data; node battery level data; electronics temperature data; or node operational fault data.

71. A method of controlling a plurality of seismic sensing nodes for ambient noise tomography (ANT), the method including: a server, including processing circuitry and having access to memory, transmitting a sensing initiation command simultaneously to a plurality of the seismic sensing nodes, each of the seismic sensing nodes being deployed as part of a spaced array of seismic sensing nodes, the spaced array extending across a region of interest, the seismic sensing nodes having their own respective power supplies, vibration sensors, and communication componentry; at least some of the seismic sensing nodes in the spaced array receiving the sensing initiation command simultaneously, to cause the seismic sensing nodes to begin passive seismic sensing for ANT; at least some of the seismic sensing nodes transmitting sensor data generated from the passive seismic sensing performed by the seismic sensing nodes while the seismic sensing nodes remain deployed across the region; the server receiving sensor data from the seismic sensing nodes while the seismic sensing nodes remain deployed across the region; the server generating a geophysical model of a sub-ground region in the region of interest based on the received sensor data; and the server transmitting a sensing termination command simultaneously to the seismic sensing nodes; at least some of the seismic sensing nodes in the spaced array receiving the sensing termination command simultaneously, to cause those seismic sensing nodes that are performing the passive seismic sensing to stop the passive seismic sensing.

72. A system for ambient noise tomography including: a server including processing circuitry and having access to memory; and a plurality of seismic sensing nodes for ambient noise tomography (ANT), the seismic sensing nodes having their own respective power supplies, vibration sensors, and communication componentry, at least some of the seismic sensing nodes deployed as part of a spaced array of seismic sensing nodes, the spaced array extending across a region of interest; wherein the memory stores program code that, when executed by the processing circuity, causes the processing circuity to: transmit a sensing initiation command simultaneously to a plurality of the seismic sensing nodes to cause the seismic sensing nodes to begin passive seismic sensing for ANT; receive sensor data from the seismic sensing nodes while the seismic sensing nodes remain deployed across the region; generate a geophysical model of a sub-ground region in the region of interest based on the received sensor data; and transmit a sensing termination command simultaneously to the seismic sensing nodes to cause the seismic sensing nodes to stop the passive seismic sensing, and wherein the communication componentry is configured to: receive the sensing initiation command simultaneously, to cause the seismic sensing nodes to begin passive seismic sensing for ANT; transmit sensor data generated from the passive seismic sensing performed by the seismic sensing nodes while the seismic sensing nodes remain deployed across the region; and receive the sensing termination command simultaneously, to cause those seismic sensing nodes that are performing the passive seismic sensing to stop the passive seismic sensing.

FURTHER CLAUSES DESCRIBING EMBODIMENTS

1. A method of controlling geophysical sensing nodes, the method comprising: transmitting a sensing initiation command simultaneously to a plurality of the sensing nodes to cause the sensing nodes to begin passive measurement, the sensing nodes being deployed as part of a spaced array of sensing nodes, the spaced array extending across a region of interest, the sensing nodes having their own respective power supplies, sensors, and communication componentry; receiving sensor measurement data from the sensing nodes while the sensing nodes remain deployed across the region; receiving sensor performance data from a plurality of the sensing nodes; generating a geophysical model of a sub-ground region in the region of interest based on the received sensor measurement data; and responsive to determining, based on the sensor performance data, that at least one of the sensing nodes is degraded, transmitting a sensing termination command to the at least one degraded sensing node to cause the at least one degraded sensing node to stop the passive measurement.

2. The method of clause 1 wherein the sensor performance data includes power consumption. 3. The method of clause 2 further comprising determining that at least one sensing node is degraded on determining that a power consumption of the at least one sensing node is below a normal power consumption range.

4. The method of clause 2 or clause 3 further comprising determining that at least one sensing node is degraded on determining that a power consumption of the at least one sensing node is above a normal power consumption range.

5. The method of any one of clauses 2 to 4 further comprising determining that at least one sensing node is degraded on observing a change in power consumption of the at least one sensing node that is above a threshold rate of change.

6. The method of any one of clauses 1 to 5 wherein the sensor performance data includes software uptime.

7. The method of clause 6 further comprising determining that at least one sensing node is degraded on determining that a software uptime is below an expected software uptime range.

8. The method of clause 6 or clause 7 further comprising determining that at least one sensing node is degraded on determining that a software uptime is above an expected software uptime range.

9. The method of any one of clauses 1 to 8 wherein the sensor performance data includes hardware performance data.

10. The method of clause 9 further comprising determining that at least one sensing node is degraded on detecting a malfunction in at least one hardware component of the at least one sensing node.

11. The method of any one of clauses 1 to 10 wherein the sensor performance data includes current draw. 12. The method of clause 11 further comprising determining that at least one sensing node is degraded on determining that a current draw of at least one component of the at least one sensing node is below a normal current draw range.

13. The method of clause 11 or clause 12 further comprising determining that at least one sensing node is degraded on determining that a current draw of at least one component of the at least one sensing node is above a normal current draw range.

14. The method of any one of clauses 11 to 13 further comprising determining that at least one sensing node is degraded on determining that a current draw of at least one component of the at least one sensing node is displaying an abnormal current pattern.

15. The method of any one of clauses 1 to 14 wherein the sensor performance data includes an operational state of at least one peripheral device.

16. The method of clause 15 further comprising determining that at least one sensing node is degraded on determining that an operational state of the at least one peripheral device of the at least one sensing node is an abnormal operational state.

17. The method of any one of clauses 1 to 16, further including: monitoring the geophysical model as it is generated to determine whether at least one model quality criterion is met; and responsive to determining that the at least one model quality criterion has been met, transmitting a sensing termination command to the sensing nodes to cause the sensing nodes to stop the passive measurement.

18. The method of clause 17, wherein the at least one model quality criterion includes one or more of: a calculated signal to noise ratio of the sensor measurement data; a calculated cross-correlation signal to noise ratio representative of at least one of the sensing nodes within the spaced array; a model spatial resolution criterion of at least part of a model volume of the sub-ground region; a threshold time duration; a threshold number of sensing nodes that are operating within the spaced array; or a threshold battery capacity among at least one of the sensing nodes within the spaced array.

19. The method of clause 17 or clause 18, wherein the at least one model quality criterion includes a rate of change of a calculated signal to noise ratio of the sensor measurement data.

20. The method of any one of clauses 17 to 19 wherein the at least one model quality criterion includes a comparison of the generated geophysical model with a previously generated geophysical model.

21. The method of any one of clauses 1 to 20, further including receiving operational status data from a plurality of the sensing nodes, the operational status data including at least one of: node location data; node orientation data; node battery level data; electronics temperature data; or node operational fault data.

22. The method of clause 21 further comprising: responsive to determining, based on the operational status data, that a number of the sensing nodes that are operating correctly is below a threshold, transmitting a sensing termination command to the sensing nodes to cause the sensing nodes to stop the passive measurement.

23. The method of any one of clauses 1 to 22, wherein the receiving includes receiving the sensor data via at least one satellite.

24. The method of any one of clauses 1 to 22, wherein the receiving includes receiving the sensor data via at least one low earth orbit satellite and/or at least one geostationary satellite. 25. The method of any one of clauses 1 to 24, wherein the transmitting is performed by a server in wireless communication with the sensing nodes via one or more satellites.

26. The method of any one of clauses 1 to 25, wherein the sensing termination command is to cause each of the sensing nodes to enter a low-power standby mode in which passive measurement is not performed by the sensing nodes.

27. The method of any one of clauses 1 to 26, further including, prior to transmitting the sensing initiation command, registering each of the sensing nodes as part of the array and receiving an indication that each sensing node in the array is in low-power standby mode.

28. The method of clause 27, further including, after the registering and prior to transmitting the sensing initiation command, deploying the sensing nodes in the spaced array.

29. The method of any one of clauses 1 to 28, wherein the receiving includes receiving sensor data over a plurality of days between about 3 days and about 12 days.

30. The method of any one of clauses 1 to 29, wherein the receiving includes receiving the sensor data continuously until the sensing termination command causes the sensing nodes to stop passive measurement.

31. The method of any one of clauses 1 to 30, wherein the received sensor data is 1-bit normalised data.

32. The method of any one of clauses 1 to 31, wherein the communication componentry includes a wireless modem.

33. The method of clause 32, wherein the wireless modem includes a satellite modem.

34. The method of any one of clauses 1 to 33, further including, after transmitting the sensing termination command, redeploying the sensing nodes in a redeployed spaced array of the sensing nodes to perform passive measurement in a different region of interest. 35. The method of clause 34, wherein the redeploying is performed without recharging the sensing nodes.

36. The method of clause 34 or clause 35, further including, after the redeploying, transmitting a further sensing initiation command to cause some or all of the redeployed array of sensing nodes to begin passive measurement to generate further sensor data in relation to the different region of interest.

37. The method of clause 36, further including: generating a further geophysical model of a sub-ground region in the different region of interest based on the received further sensor measurement data; and transmitting a further sensing termination command simultaneously to the sensing nodes in the redeployed array to cause the sensing nodes to stop the passive measurement.

38. A geophysical sensing system comprising: processing circuitry; and memory storing program code that, when executed by processing circuity, causes the processing circuity to perform the method of any one of clauses 1 to 37.

39. A geophysical sensing system comprising: a server including processing circuitry and having access to memory; wherein the memory stores program code that, when executed by the processing circuity, causes the processing circuity to: transmit a sensing initiation command simultaneously to a plurality of the sensing nodes to cause the sensing nodes to begin passive measurement, the sensing nodes being deployed as part of a spaced array of sensing nodes, the spaced array extending across a region of interest, the sensing nodes having their own respective power supplies, vibration sensors, and communication componentry; receive sensor measurement data from the sensing nodes while the sensing nodes remain deployed across the region; receive sensor performance data from a plurality of the sensing nodes; generate a geophysical model of a sub-ground region in the region of interest based on the received sensor measurement data; and responsive to determining, based on the sensor performance data, that at least one of the sensing nodes is degraded, transmit a sensing termination command to the at least one degraded sensing node to cause the at least one degraded sensing node to stop the passive measurement.

40. The system of clause 39 wherein the sensor performance data includes power consumption.

41. The system of clause 40 wherein the program code causes the processing circuity to determine that at least one sensing node is degraded on determining that a power consumption of the at least one sensing node is below a normal power consumption range.

42. The system of clause 40 or clause 41 wherein the program code causes the processing circuitry to determine that at least one sensing node is degraded on determining that a power consumption of the at least one sensing node is above a normal power consumption range.

43. The system of any one of clauses 40 to 42 wherein the program code causes the processing circuitry to determine that at least one sensing node is degraded on observing a change in power consumption of the at least one sensing node that is above a threshold rate of change.

44. The system of any one of clauses 39 to 43 wherein the sensor performance data includes software uptime.

45. The system of clause 44 wherein the program code causes the processing circuitry to determine that at least one sensing node is degraded on determining that a software uptime is below an expected software uptime range. 46. The system of clause 44 or clause 45 wherein the program code causes the processing circuitry to determine that at least one sensing node is degraded on determining that a software uptime is above an expected software uptime range.

47. The system of any one of clauses 39 to 46 wherein the sensor performance data includes hardware performance data.

48. The system of clause 47 wherein the program code causes the processing circuitry to determine that at least one sensing node is degraded on detecting a malfunction in at least one hardware component of the at least one sensing node.

49. The system of any one of clauses 39 to 48 wherein the sensor performance data includes current draw.

50. The system of clause 49 wherein the program code causes the processing circuitry to determine that at least one sensing node is degraded on determining that a current draw of at least one component of the at least one sensing node is below a normal current draw range.

51. The system of clause 49 or clause 50 wherein the program code causes the processing circuitry to determine that at least one sensing node is degraded on determining that a current draw of at least one component of the at least one sensing node is above a normal current draw range.

52. The system of any one of clauses 49 to 51 wherein the program code causes the processing circuitry to determine that at least one sensing node is degraded on determining that a current draw of at least one component of the at least one sensing node is displaying an abnormal current pattern.

53. The system of any one of clauses 39 to 52 wherein the sensor performance data includes an operational state of at least one peripheral device. 54. The system of clause 53 wherein the program code causes the processing circuitry to determine that at least one sensing node is degraded on determining that an operational state of the at least one external peripheral device of the at least one sensing node is an abnormal operational state.

55. The system of any one of clauses 39 to 54, wherein the program code causes the processing circuitry to: monitor the geophysical model as it is generated to determine whether at least one model quality criterion is met; and responsive to determining that the at least one model quality criterion has been met, transmit a sensing termination command to the sensing nodes to cause the sensing nodes to stop the passive measurement.

56. The system of clause 55, wherein the at least one model quality criterion includes one or more of: a calculated signal to noise ratio of the sensor measurement data; a calculated cross-correlation signal to noise ratio representative of at least one of the data acquisition units within the spaced array; a model spatial resolution criterion of at least part of a model volume of the sub-ground region; a threshold time duration; a threshold number of data acquisition units that are operating within the spaced array; or a threshold battery capacity among at least one of the data acquisition units within the spaced array.

57. The system of clause 55 or clause 56, wherein the at least one model quality criterion includes a rate of change of a calculated signal to noise ratio of the sensor measurement data.

58. The system of any one of clauses 55 to 57 wherein the at least one model quality criterion includes a comparison of the generated geophysical model with a previously generated geophysical model. 59. The system of any one of clauses 39 to 58, wherein the program code causes the processing circuitry to receive operational status data from a plurality of the sensing nodes, the operational status data including at least one of: node location data; node orientation data; node battery level data; electronics temperature data; or node operational fault data.

60. The system of clause 59 wherein the program code causes the processing circuitry, responsive to determining, based on the operational status data, that a number of the sensing nodes that are operating correctly is below a threshold, to transmitr a sensing termination command to the sensing nodes to cause the sensing nodes to stop the passive measurement.

61. The system of any one of clauses 39 to 60, wherein the receiving includes receiving the sensor data via at least one satellite.

61. The system of any one of clauses 39 to 60, wherein the receiving includes receiving the sensor data via at least one low earth orbit satellite and/or at least one geostationary satellite.

62. The system of any one of clauses 39 to 61, wherein the transmitting is performed by a server in wireless communication with the sensing nodes via one or more satellites.

63. The system of any one of clauses 39 to 62, wherein the sensing termination command is to cause each of the sensing nodes to enter a low-power standby mode in which passive measurement is not performed by the sensing nodes.

64. The system of any one of clauses 39 to 63, wherein the program code causes the processing circuitry, prior to transmitting the sensing initiation command, to register each of the sensing nodes as part of the array and receiving an indication that each sensing node in the array is in low-power standby mode.

65. The system of clause 64, wherein the program code causes the processing circuitry, after the registering and prior to transmitting the sensing initiation command, to deploy the sensing nodes in the spaced array. 66. The system of any one of clauses 39 to 65, wherein the receiving includes receiving sensor data over a plurality of days between about 3 days and about 12 days.

67. The system of any one of clauses 39 to 66, wherein the receiving includes receiving the sensor data continuously until the sensing termination command causes the sensing nodes to stop passive measurement.

68. The system of any one of clauses 39 to 67, wherein the received sensor data is 1-bit normalised data.

69. The system of any one of clauses 39 to 68, wherein the communication componentry includes a wireless modem.

70. The system of clause 69, wherein the wireless modem includes a satellite modem.

71. The system of any one of clauses 39 to 70, wherein the program code causes the processing circuitry, after transmitting the sensing termination command, to redeploy the sensing nodes in a redeployed spaced array of the sensing nodes to perform ANT in a different region of interest.

72. The system of clause 71, wherein the redeploying is performed without recharging the sensing nodes.

73. The system of clause 71 or clause 72, wherein the program code causes the processing circuitry, after the redeploying, transmitting a further sensing initiation command to cause some or all of the redeployed array of sensing nodes to begin passive sensing of seismic vibrations to generate further sensor data in relation to the different region of interest.

74. The system of clause 73, wherein the program code causes the processing circuitry to: generate a further geophysical model of a sub-ground region in the different region of interest based on the received further sensor data; and transmit a further sensing termination command simultaneously to the sensing nodes in the redeployed array to cause the sensing nodes to stop the passive seismic sensing.

75. A method of controlling a plurality of sensing nodes, at least some of the sensing nodes being deployed as part of a spaced array of sensing nodes, the spaced array extending across a region of interest, wherein the sensing nodes have their own respective power supplies, sensors, and communication componentry, the method comprising: at least some of the sensing nodes in the spaced array receiving a sensing initiation command simultaneously, to cause the sensing nodes to begin passive seismic sensing for ANT; transmitting sensor measurement data generated from the passive seismic sensing performed by the sensing nodes while the sensing nodes remain deployed across the region, for generation of a geophysical model of a sub-ground region in the region of interest based on the received sensor measurement data; transmitting sensor performance data from a plurality of the sensing nodes; and responsive to a determination, based on the sensor performance data, that at least one of the sensing nodes is degraded, the at least one degraded seismic sensing node receiving a sensing termination command to cause the at least one degraded seismic sensing node to stop the passive seismic sensing.

76. A geophysical sensing system including a plurality of sensing nodes, the sensing nodes having their own respective power supplies, sensors, and communication componentry, the communication componentry configured to perform the method of clause 75.

77. A geophysical sensing system comprising: a plurality of sensing nodes for ambient noise tomography (ANT), the sensing nodes having their own respective power supplies, vibration sensors, and communication componentry, at least some of the sensing nodes deployed as part of a spaced array of sensing nodes, the spaced array extending across a region of interest, the communication componentry configured to: receive a sensing initiation command simultaneously, to cause the sensing nodes to begin passive seismic sensing for ANT; transmit sensor measurement data generated from the passive seismic sensing performed by the sensing nodes while the sensing nodes remain deployed across the region, for generation of a geophysical model of a sub-ground region in the region of interest based on the received sensor measurement data; transmit sensor performance data from a plurality of the sensing nodes; and responsive to a determination, based on the sensor performance data, that at least one of the sensing nodes is degraded, receive a sensing termination command to cause the at least one degraded seismic sensing node to stop the passive seismic sensing.

78. A method of controlling a plurality of sensing nodes, by a server in communication with the plurality of sensing nodes, the server including processing circuitry and having access to memory, the method comprising: the server transmitting a sensing initiation command simultaneously to a plurality of the sensing nodes, the sensing nodes being deployed as part of a spaced array of sensing nodes, the spaced array extending across a region of interest, the sensing nodes having their own respective power supplies, vibration sensors, and communication componentry; at least some of the sensing nodes in the spaced array receiving the sensing initiation command simultaneously, to cause the sensing nodes to begin passive seismic sensing for ANT; at least some of the sensing nodes transmitting sensor measurement data generated from the passive seismic sensing performed by the sensing nodes while the sensing nodes remain deployed across the region; at least some of the sensing nodes transmitting sensor performance data from a plurality of the sensing nodes; the server receiving the sensor measurement data from the sensing nodes while the sensing nodes remain deployed across the region; the server generating a geophysical model of a sub-ground region in the region of interest based on the received sensor measurement data; the server receiving the sensor performance data from a plurality of the sensing nodes; and responsive to determining, based on the sensor performance data, that at least one of the sensing nodes is degraded, the server transmitting a sensing termination command to the at least one degraded seismic sensing node; and the at least one degraded seismic sensing node receiving the sensing termination command, to cause the at least one degraded seismic sensing node to stop the passive seismic sensing.

79. A geophysical sensing system comprising: a server including processing circuitry and having access to memory; and a plurality of sensing nodes for ambient noise tomography (ANT), the sensing nodes having their own respective power supplies, vibration sensors, and communication componentry, at least some of the sensing nodes deployed as part of a spaced array of sensing nodes, the spaced array extending across a region of interest; wherein the memory stores program code that, when executed by the processing circuity, causes the processing circuity to: transmit a sensing initiation command simultaneously to a plurality of the sensing nodes to cause the sensing nodes to begin passive seismic sensing for ANT; receive sensor measurement data from the sensing nodes while the sensing nodes remain deployed across the region; receive sensor performance data from a plurality of the sensing nodes; generate a geophysical model of a sub-ground region in the region of interest based on the received sensor measurement data; and responsive to determining, based on the sensor performance data, that at least one of the sensing nodes is degraded, transmit a sensing termination command to the at least one degraded seismic sensing node to cause the at least one degraded seismic sensing node to stop the passive seismic sensing, and wherein the communication componentry of the respective sensing nodes is configured to: receive the sensing initiation command, to cause the sensing nodes to begin passive sensing for ANT; transmit sensor measurement data generated from the passive seismic sensing performed by the sensing nodes while the sensing nodes remain deployed across the region; transmit the sensor performance data; and the at least one degraded seismic sensing node receive the sensing termination command to stop the passive seismic sensing.

80. A method of controlling geophysical sensing nodes, the method comprising: transmitting a sensing initiation command simultaneously to a plurality of the sensing nodes to cause the sensing nodes to begin passive measurement, the sensing nodes being deployed as part of a spaced array of sensing nodes, the spaced array extending across a region of interest, the sensing nodes having their own respective power supplies, sensors, and communication componentry; receiving sensor measurement data from the sensing nodes while the sensing nodes remain deployed across the region; generating a geophysical model of a sub-ground region in the region of interest based on the received sensor measurement data; monitoring the geophysical model as it is generated to determine whether at least one model quality criterion is met; and responsive to determining that the at least one model quality criterion has been met, transmitting a sensing termination command to the sensing nodes to cause the sensing nodes to stop the passive measurement.

81. A geophysical sensing system comprising: a server including processing circuitry and having access to memory; wherein the memory stores program code that, when executed by the processing circuity, causes the processing circuity to: transmit a sensing initiation command simultaneously to a plurality of the sensing nodes to cause the sensing nodes to begin passive measurement, the sensing nodes being deployed as part of a spaced array of sensing nodes, the spaced array extending across a region of interest, the sensing nodes having their own respective power supplies, vibration sensors, and communication componentry; receive sensor measurement data from the sensing nodes while the sensing nodes remain deployed across the region; generate a geophysical model of a sub-ground region in the region of interest based on the received sensor measurement data; monitor the geophysical model as it is generated to determine whether at least one model quality criterion is met; and responsive to determining that the at least one model quality criterion has been met, transmit a sensing termination command to the sensing nodes to cause the sensing nodes to stop the passive measurement.

Claims

CLAIMS:

1. A method of controlling seismic sensing nodes for ambient noise tomography (ANT), the method comprising: transmitting a sensing initiation command simultaneously to a plurality of the seismic sensing nodes to cause the seismic sensing nodes to begin passive seismic sensing for ANT, each of the seismic sensing nodes being deployed as part of a spaced array of seismic sensing nodes, the spaced array extending across a region of interest, the seismic sensing nodes having their own respective power supplies, vibration sensors, and communication componentry; receiving sensor data from the seismic sensing nodes while the seismic sensing nodes remain deployed across the region; generating a geophysical model of a sub-ground region in the region of interest based on the received sensor data; and transmitting a sensing termination command simultaneously to the seismic sensing nodes to cause the seismic sensing nodes to stop the passive seismic sensing.

2. The method of claim 1, wherein the receiving includes receiving the sensor data via at least one satellite.

3. The method of claim 1, wherein the receiving includes receiving the sensor data via at least one low earth orbit satellite and/or at least one geostationary satellite.

4. The method of any one of claims 1 to 3, wherein the transmitting is performed by a server in wireless communication with the seismic sensing nodes via one or more satellites.

5. The method of any one of claims 1 to 4, wherein the sensing termination command is to cause each of the seismic sensing nodes to enter a low-power standby mode in which passive seismic sensing is not performed by the seismic sensing nodes.

6. The method of any one of claims 1 to 5, further including, prior to transmitting the sensing initiation command, registering each of the seismic sensing nodes as part of the array and receiving an indication that each seismic sensing node in the array is in low-power standby mode.

7. The method of claim 6, further including, after the registering and prior to transmitting the sensing initiation command, deploying the seismic sensing nodes in the spaced array.

8. The method of any one of claims 1 to 7, further including monitoring the geophysical model as it is generated to determine whether at least one data criterion is met, wherein the sensing termination command is transmitted in response to determining that the at least one data criterion has been met.

9. The method of claim 8, wherein the at least one criterion includes one or more of: a calculated signal to noise ratio of the sensor data; a calculated cross-correlation signal to noise ratio representative of at least one of the data acquisition units within the spaced array; a model spatial resolution criterion of at least part of a model volume of the sub-ground region; a threshold time duration; a threshold number of data acquisition units that are operating within the spaced array; or a threshold battery capacity among at least one of the data acquisition units within the spaced array.

10. The method of any one of claims 1 to 9, wherein the receiving includes receiving sensor data over a plurality of days between about 3 days and about 12 days.

11. The method of any one of claims 1 to 10, wherein the receiving includes receiving the sensor data continuously until the sensing termination command causes the seismic sensing nodes to stop seismic sensing.

12. The method of any one of claims 1 to 11, wherein the received sensor data is 1-bit normalised data.

13. The method of any one of claims 1 to 12, wherein the communication componentry includes a wireless modem.

14. The method of claim 13, wherein the wireless modem includes a satellite modem.

15. The method of any one of claims 1 to 14, further including, after transmitting the sensing termination command, redeploying the seismic sensing nodes in a redeployed spaced array of the seismic sensing nodes to perform ANT in a different region of interest.

16. The method of claim 15, wherein the redeploying is performed without recharging the seismic sensing nodes.

17. The method of claim 15 or claim 16, further including, after the redeploying, transmitting a further sensing initiation command to cause some or all of the redeployed array of seismic sensing nodes to begin passive sensing of seismic vibrations to generate further sensor data in relation to the different region of interest.

18. The method of claim 17, further including: generating a further geophysical model of a sub-ground region in the different region of interest based on the received further sensor data; and transmitting a further sensing termination command simultaneously to the seismic sensing nodes in the redeployed array to cause the seismic sensing nodes to stop the passive seismic sensing.

19. The method of any one of claims 1 to 18, further including receiving operational status data from each of the seismic sensing nodes, the operational status data including at least one of: node location data; node orientation data; node battery level data; electronics temperature data; or node operational fault data.

20. A system for ambient noise tomography comprising: processing circuitry; and memory storing program code that, when executed by processing circuity, causes the processing circuity to perform the method of any one of claims 1 to 19.

21. A system for ambient noise tomography comprising: a server including processing circuitry and having access to memory; wherein the memory stores program code that, when executed by the processing circuity, causes the processing circuity to: transmit a sensing initiation command simultaneously to a plurality of the seismic sensing nodes to cause the seismic sensing nodes to begin passive seismic sensing for ANT, each of the seismic sensing nodes being deployed as part of a spaced array of seismic sensing nodes, the spaced array extending across a region of interest, the seismic sensing nodes having their own respective power supplies, vibration sensors, and communication componentry; receive sensor data from the seismic sensing nodes while the seismic sensing nodes remain deployed across the region; generate a geophysical model of a sub-ground region in the region of interest based on the received sensor data; and transmit a sensing termination command simultaneously to the seismic sensing nodes to cause the seismic sensing nodes to stop the passive seismic sensing.

22. The system of claim 21 wherein the receiving performed by the processing circuitry includes receiving the sensor data via at least one satellite.

23. The system of claim 21 wherein the receiving performed by the processing circuitry includes receiving the sensor data via at least one low earth orbit satellite and/or at least one geostationary satellite.

24. The system of any one of claims 21 to 23 wherein the transmitting performed by the processing circuitry is performed in wireless communication with the seismic sensing nodes via one or more satellites.

25. The system of any one of claims 21 to 24 wherein the sensing termination command is to cause each of the seismic sensing nodes to enter a low-power standby mode in which passive seismic sensing is not performed by the seismic sensing nodes.

26. The system of any one of claims 21 to 25 wherein the program code further causes the processing circuitry to, prior to the transmission of the sensing initiation command, register each of the seismic sensing nodes as part of the array and receive an indication that each seismic sensing nodes in the array is in low-power standby mode.

27. The system of any one of claims 21 to 26 wherein the program code further causes the processing circuitry to monitor the geophysical model as it is generated to determine whether at least one data criterion is met, wherein the sensing termination command is transmitted in response to determining that the at least one data criterion has been met.

28. The system of claim 27, wherein the at least one criterion includes one or more of: a calculated signal to noise ratio of the sensor data; a calculated cross-correlation signal to noise ratio representative of at least one of the data acquisition units within the spaced array; a model spatial resolution criterion of at least part of a model volume of the sub-ground region; a threshold time duration; a threshold number of data acquisition units that are operating within the spaced array; or a threshold battery capacity among at least one of the data acquisition units within the spaced array.

29. The system of any one of claims 21 to 28 wherein the receiving includes receiving sensor data over a plurality of days between about 3 days and about 12 days.

30. The system of any one of claims 21 to 29 wherein the receiving includes receiving the sensor data continuously until the sensing termination command causes the seismic sensing nodes to stop seismic sensing.

31. The system of any one of claims 21 to 30 wherein the received sensor data is 1-bit normalised data.

32. The system of any one of claims 21 to 31, wherein the program code further causes the processing circuitry to, after redeployment of the seismic sensing nodes in a redeployed spaced array of the seismic sensing nodes to perform ANT in a different region of interest, transmit a further sensing initiation command to cause some or all of the redeployed array of seismic sensing nodes to begin passive sensing of seismic vibrations to generate further sensor data in relation to the different region of interest.

33. The system of claim 32, wherein the program code further causes the processing circuitry to: generate a further geophysical model of a sub-ground region in the different region of interest based on received further sensor data; and transmit a further sensing termination command simultaneously to the seismic sensing nodes in the redeployed array to cause the seismic sensing nodes to stop the passive seismic sensing.

34. The system of any one of claims 21 to 33, wherein the program code further causes the processing circuitry to receive operational status data from each of the seismic sensing nodes, the operation status data including at least one of: node location data; node orientation data; node battery level data; electronics temperature data; or node operational fault data.

35. A method of controlling a plurality of seismic sensing nodes for ambient noise tomography (ANT), at least some of the seismic sensing nodes being deployed as part of a spaced array of seismic sensing nodes, the spaced array extending across a region of interest, wherein the seismic sensing nodes have their own respective power supplies, vibration sensors, and communication componentry, the method comprising: at least some of the seismic sensing nodes in the spaced array receiving a sensing initiation command simultaneously, to cause the seismic sensing nodes to begin passive seismic sensing for ANT; transmitting sensor data generated from the passive seismic sensing performed by the seismic sensing nodes while the seismic sensing nodes remain deployed across the region, for generation of a geophysical model of a sub-ground region in the region of interest based on the received sensor data; at least some of the seismic sensing nodes in the spaced array receiving a sensing termination command simultaneously, to cause those seismic sensing nodes that are performing the passive seismic sensing to stop the passive seismic sensing.

36. A system for ambient noise tomography comprising a plurality of seismic sensing nodes for ambient noise tomography (ANT), the seismic sensing nodes having their own respective power supplies, vibration sensors, and communication componentry, the communication componentry configured to perform the method of claim 35.

37. A system for ambient noise tomography comprising: a plurality of seismic sensing nodes for ambient noise tomography (ANT), the seismic sensing nodes having their own respective power supplies, vibration sensors, and communication componentry, at least some of the seismic sensing nodes deployed as part of a spaced array of seismic sensing nodes, the spaced array extending across a region of interest, the communication componentry configured to: receive a sensing initiation command simultaneously, to cause the seismic sensing nodes to begin passive seismic sensing for ANT; transmit sensor data generated from the passive seismic sensing performed by the seismic sensing nodes while the seismic sensing nodes remain deployed across the region, for generation of a geophysical model of a sub-ground region in the region of interest based on the received sensor data; and receive a sensing termination command simultaneously, to cause those seismic sensing nodes that are performing the passive seismic sensing to stop the passive seismic sensing.

38. A method of controlling a plurality of seismic sensing nodes for ambient noise tomography (ANT), by a server in communication with the plurality of seismic sensing nodes, the server including processing circuitry and having access to memory, the method comprising: the server transmitting a sensing initiation command simultaneously to a plurality of the seismic sensing nodes, each of the seismic sensing nodes being deployed as part of a spaced array of seismic sensing nodes, the spaced array extending across a region of interest, the seismic sensing nodes having their own respective power supplies, vibration sensors, and communication componentry; at least some of the seismic sensing nodes in the spaced array receiving the sensing initiation command simultaneously, to cause the seismic sensing nodes to begin passive seismic sensing for ANT; at least some of the seismic sensing nodes transmitting sensor data generated from the passive seismic sensing performed by the seismic sensing nodes while the seismic sensing nodes remain deployed across the region; the server receiving sensor data from the seismic sensing nodes while the seismic sensing nodes remain deployed across the region; the server generating a geophysical model of a sub-ground region in the region of interest based on the received sensor data; and the server transmitting a sensing termination command simultaneously to the seismic sensing nodes; at least some of the seismic sensing nodes in the spaced array receiving the sensing termination command simultaneously, to cause those seismic sensing nodes that are performing the passive seismic sensing to stop the passive seismic sensing.

39. A system for ambient noise tomography comprising: a server including processing circuitry and having access to memory; and a plurality of seismic sensing nodes for ambient noise tomography (ANT), the seismic sensing nodes having their own respective power supplies, vibration sensors, and communication componentry, at least some of the seismic sensing nodes deployed as part of a spaced array of seismic sensing nodes, the spaced array extending across a region of interest; wherein the memory stores program code that, when executed by the processing circuity, causes the processing circuity to: transmit a sensing initiation command simultaneously to a plurality of the seismic sensing nodes to cause the seismic sensing nodes to begin passive seismic sensing for ANT; receive sensor data from the seismic sensing nodes while the seismic sensing nodes remain deployed across the region; generate a geophysical model of a sub-ground region in the region of interest based on the received sensor data; and transmit a sensing termination command simultaneously to the seismic sensing nodes to cause the seismic sensing nodes to stop the passive seismic sensing, and wherein the communication componentry of each seismic sensing node is configured to: receive the sensing initiation command, to cause the seismic sensing nodes to begin passive seismic sensing for ANT; transmit sensor data generated from the passive seismic sensing performed by the seismic sensing nodes while the seismic sensing nodes remain deployed across the region; and receive the sensing termination command, to cause those seismic sensing nodes that are performing the passive seismic sensing to stop the passive seismic sensing.

40. A method of controlling geophysical sensing nodes, the method comprising: transmitting a sensing initiation command simultaneously to a plurality of the sensing nodes to cause the sensing nodes to begin passive measurement, the sensing nodes being deployed as part of a spaced array of sensing nodes, the spaced array extending across a region of interest, the sensing nodes having their own respective power supplies, sensors, and communication componentry; receiving sensor measurement data from the sensing nodes while the sensing nodes remain deployed across the region; receiving sensor performance data from a plurality of the sensing nodes; generating a geophysical model of a sub-ground region in the region of interest based on the received sensor measurement data; and responsive to determining, based on the sensor performance data, that at least one of the sensing nodes is degraded, transmitting a sensing termination command to the at least one degraded sensing node to cause the at least one degraded sensing node to stop the passive measurement.

41. The method of claim 40 wherein the sensor performance data includes power consumption, the method further comprising determining that at least one sensing node is degraded on determining that a power consumption of the at least one sensing node is above a normal power consumption range.

42. The method of claim 40 or claim 41 wherein the sensor performance data includes software uptime, the method further comprising determining that at least one sensing node is degraded on determining that a software uptime is below an expected software uptime range.

43. The method of any one of claims 40 to 42, further comprising: monitoring the geophysical model as it is generated to determine whether at least one model quality criterion is met; and responsive to determining that the at least one model quality criterion has been met, transmitting a sensing termination command to the sensing nodes to cause the sensing nodes to stop the passive measurement.

44. The method of claim 43, wherein the at least one model quality criterion includes one or more of: a calculated signal to noise ratio of the sensor measurement data; a calculated cross-correlation signal to noise ratio representative of at least one of the sensing nodes within the spaced array; a model spatial resolution criterion of at least part of a model volume of the sub-ground region; a threshold time duration; a threshold number of sensing nodes that are operating within the spaced array; or a threshold battery capacity among at least one of the sensing nodes within the spaced array.

45. A geophysical sensing system comprising: a server including processing circuitry and having access to memory; wherein the memory stores program code that, when executed by the processing circuity, causes the processing circuity to: transmit a sensing initiation command simultaneously to a plurality of the sensing nodes to cause the sensing nodes to begin passive measurement, the sensing nodes being deployed as part of a spaced array of sensing nodes, the spaced array extending across a region of interest, the sensing nodes having their own respective power supplies, vibration sensors, and communication componentry; receive sensor measurement data from the sensing nodes while the sensing nodes remain deployed across the region; receive sensor performance data from a plurality of the sensing nodes; generate a geophysical model of a sub-ground region in the region of interest based on the received sensor measurement data; and responsive to determining, based on the sensor performance data, that at least one of the sensing nodes is degraded, transmit a sensing termination command to the at least one degraded sensing node to cause the at least one degraded sensing node to stop the passive measurement.

46. The system of claim 45 wherein the sensor performance data includes power consumption, and wherein the program code causes the processing circuitry to determine that at least one sensing node is degraded on determining that a power consumption of the at least one sensing node is above a normal power consumption range.

47. The system of claim 45 or claim 46 wherein the sensor performance data includes software uptime, and wherein the program code causes the processing circuitry to determine that at least one sensing node is degraded on determining that a software uptime is below an expected software uptime range.

48. The system of any one of claims 45 to 47, wherein the program code causes the processing circuitry to: monitor the geophysical model as it is generated to determine whether at least one model quality criterion is met; and responsive to determining that the at least one model quality criterion has been met, transmit a sensing termination command to the sensing nodes to cause the sensing nodes to stop the passive measurement.

49. The system of claim 48, wherein the at least one model quality criterion includes one or more of: a calculated signal to noise ratio of the sensor measurement data; a calculated cross-correlation signal to noise ratio representative of at least one of the data acquisition units within the spaced array; a model spatial resolution criterion of at least part of a model volume of the sub-ground region; a threshold time duration; a threshold number of data acquisition units that are operating within the spaced array; or a threshold battery capacity among at least one of the data acquisition units within the spaced array.