CN108627834A

CN108627834A - A kind of subway road structure monitoring method and device based on ground InSAR

Info

Publication number: CN108627834A
Application number: CN201810578148.1A
Authority: CN
Inventors: 陈林; 王思锴; 刘君伟; 王志京; 陈维桢; 范静雅; 石磊; 任雪峰
Original assignee: Beijing Urban Construction Exploration and Surveying Design Research Institute Co Ltd
Current assignee: Beijing Urban Construction Exploration and Surveying Design Research Institute Co Ltd
Priority date: 2018-06-07
Filing date: 2018-06-07
Publication date: 2018-10-09

Abstract

The embodiment of the present invention provides a kind of subway road structure monitoring method and device based on ground InSAR, the method includes：Repeated measures are carried out to target area using radar sensor on linear scan sliding rail, obtain a width synthetic aperture radar SAR image within about 10 seconds；The pixel for representing identical atural object in target area described in two width SAR images is matched to same position, carries out image registration；Interference image after image registration is to conjugate multiplicationIt can be obtained interferometric phase image；The coherence map γ of acquisition is handled into line noise filter；To carrying out phase unwrapping into line noise filter treated coherence map γ；Coherence map γ to carrying out phase unwrapping carries out atmospheric correction, obtains the deformation map of the target area；The deformation map of the target area under radar fix system is subjected to geocoding, is projected under geographic coordinate system, the deformation map after geocoding is obtained.It may be implemented disliking slightly under extreme weather or subway is overhead over long distances in (4km) range and high-precision, the successional deformation monitoring of road structure overall region.

Description

Subway roadbed structure monitoring method and device based on foundation InSAR

Technical Field

The invention relates to the field of engineering measurement, in particular to a subway roadbed structure monitoring method and device based on a foundation InSAR.

Background

Deformation monitoring needs to be carried out on the subway structure when the engineering construction of the overhead and roadbed of the crossing and adjacent subways is carried out, so that the structural deformation condition of the existing subway can be known in time, and the safety of the existing subway structure and the running safety of a train can be ensured.

During the operation of the train, in order to ensure the safe operation of the train, the deformation condition of the subway structure in the construction influence range needs to be known in time, and the non-contact remote automatic monitoring system can be adopted to solve the problem of deformation monitoring during the operation of the train. The existing automatic monitoring system mainly adopts a static level system and a measuring robot system.

The two monitoring methods have the following problems:

(1) the traditional measurement mode of the subway overhead and roadbed structure is discrete, and the integral deformation of the structure can be reflected only through point data;

(2) the traditional measuring mode of the elevated subway and the roadbed structure is influenced by the surrounding environment and the characteristics of the elevated subway and the roadbed structure, long-distance monitoring cannot be carried out, the farthest monitoring distance is about 300m, and the monitoring requirement cannot be met under special conditions;

(3) the traditional measurement mode of the traditional subway elevated and roadbed structure is difficult to realize real-time monitoring all day long under extreme conditions, if a total station belongs to an optical measurement instrument, the implementation is difficult to carry out under the condition of foggy days or rainy days; the temperature has great influence on the static level instrument equipment, and the monitoring precision is difficult to guarantee under the condition of great temperature difference.

In the process of implementing the invention, the inventor finds that at least the following problems exist in the prior art: the technical personnel in the field need to solve the problem of deformation monitoring with high precision and continuity in the whole area of subway overhead and roadbed structures in severe extreme weather or in a long distance (4 km).

Disclosure of Invention

The embodiment of the invention provides a subway roadbed structure monitoring method and device based on a foundation InSAR (interferometric synthetic aperture radar), which can realize high-precision and continuous deformation monitoring of the whole areas of subway elevated frames and roadbed structures in severe extreme weather or a long distance (4km) range.

In one aspect, an embodiment of the present invention provides a subway subgrade structure monitoring method based on a foundation InSAR, including:

repeatedly observing a target area on the linear scanning slide rail by using a radar sensor, and acquiring a Synthetic Aperture Radar (SAR) image in about 10 seconds;

matching pixels representing the same ground object in the target area in the two SAR images to the same position, and carrying out image registration;

conjugate multiplication of interference image after image registrationObtaining an interference phase diagram, and calculating to obtain a corresponding coherence diagram gamma according to the following formula:

wherein,representing conjugate multiplication of an interference image pair, wherein gamma represents a coherence map, gamma is between 0 and 1, and when gamma is equal to 0, the two images are completely incoherent; when gamma is equal to 1, the two images are the same, and the interference coherence is better;

carrying out noise filtering processing on the obtained coherence map gamma;

phase unwrapping is carried out on the coherent graph gamma after noise filtering processing;

carrying out atmospheric correction on the coherent image gamma subjected to phase unwrapping to obtain a deformation image of the target area;

and geocoding the deformation graph of the target area in the radar coordinate system, projecting the deformation graph to the geographic coordinate system, and acquiring the geocoded deformation graph.

On the other hand, the embodiment of the invention provides a subway subgrade structure monitoring device based on a foundation InSAR, which comprises:

the image acquisition unit is used for repeatedly observing a target area on the linear scanning slide rail by using the radar sensor, and acquiring a Synthetic Aperture Radar (SAR) image in about 10 seconds;

the image registration unit is used for matching the pixels representing the same ground object in the target area in the two SAR images to the same position to perform image registration;

an interference generation unit for conjugate multiplying the interference image after image registrationObtaining an interference phase diagram, and calculating to obtain a corresponding coherence diagram gamma according to the following formula:

the noise filtering unit is used for carrying out noise filtering processing on the acquired coherence map gamma;

the phase unwrapping unit is used for unwrapping the phase of the coherent graph gamma after the noise filtering processing;

the atmospheric correction unit is used for carrying out atmospheric correction on the coherent image gamma subjected to phase unwrapping to acquire a deformation image of the target area;

and the geocoding unit is used for geocoding the deformation map of the target area in the radar coordinate system, projecting the deformation map to the geographic coordinate system and acquiring the deformation map after geocoding.

The technical scheme has the following beneficial effects:

(1) the non-contact remote monitoring of the subway overhead and roadbed structures is realized. The ground-based InSAR technology can monitor a target area in a long distance without measuring whether a worker enters or contacts the monitoring area, and the farthest monitoring distance reaches 4 km. Many of the traditional measuring methods need to establish a reference point in a target area or construct a monitoring net, so that the traditional measuring methods are difficult to be applied to areas which are difficult to be accessed by people and dangerous areas.

(2) Wide coverage and high resolution. Compared with the traditional discrete point deformation measurement mode, the ground-based InSAR technology can realize continuous monitoring of a large-range target area, is very beneficial to the analysis of deformation distribution and deformation process of the target area in the later period, and overcomes the defects of large workload and low resolution of discrete point deformation measurement.

(3) The measurement precision is high. The traditional measurement mode can reach millimeter level in precision under the better condition of observation condition, and the foundation InSAR measurement precision can reach submillimeter level.

(4) And (5) all-weather real-time monitoring. Many traditional measurement methods are difficult to realize all-day real-time monitoring, and if a total station belongs to an optical measurement instrument, the total station is difficult to implement in foggy days or rainy days; GPS monitoring has high requirements on satellite signals and weather conditions, and an antenna cannot be shielded by tall objects.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a flow chart of a subway roadbed structure monitoring method based on a foundation InSAR according to an embodiment of the invention;

fig. 2 is a schematic structural diagram of a subway subgrade structure monitoring device based on a foundation InSAR according to an embodiment of the invention;

FIG. 3 is a schematic diagram of a noise filtering unit according to an embodiment of the present invention;

FIG. 4 is a diagram illustrating a specific principle of a synthetic aperture radar technology according to an embodiment of the present invention;

FIG. 5 is a geometric schematic of a two-trace differential interferometry measurement in accordance with an embodiment of the present invention;

FIG. 6 is a schematic view of a process flow of a ground-based SAR interferometry data processing of an exemplary application of the present invention;

FIG. 7 is a graph of the reflection intensity of a target signal according to an exemplary embodiment of the present invention;

FIG. 8 is a time sequence diagram of the deformation of monitoring points according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 1, a flow chart of a subway subgrade structure monitoring method based on a foundation InSAR according to an embodiment of the present invention is shown, where the method includes:

101. repeatedly observing a target area on the linear scanning slide rail by using a radar sensor, and acquiring a Synthetic Aperture Radar (SAR) image in about 10 seconds;

102. matching pixels representing the same ground object in the target area in the two SAR images to the same position, and carrying out image registration;

103. conjugate multiplication of interference image after image registrationObtaining an interference phase diagram, and calculating to obtain a corresponding coherence diagram gamma according to the following formula:

104. carrying out noise filtering processing on the obtained coherence map gamma;

105. phase unwrapping is carried out on the coherent graph gamma after noise filtering processing;

106. carrying out atmospheric correction on the coherent image gamma subjected to phase unwrapping to obtain a deformation image of the target area;

107. and geocoding the deformation graph of the target area in the radar coordinate system, projecting the deformation graph to the geographic coordinate system, and acquiring the geocoded deformation graph.

Preferably, the target area is repeatedly observed on the linear scanning slide rail by using the radar sensor, and after a synthetic aperture radar SAR image is obtained in about 10 seconds, the obtained original SAR image is filtered;

conjugate multiplication of interference image after image registrationAnd filtering after obtaining a corresponding coherence map gamma.

Preferably, the coherent map γ after the noise filtering process is phase unwrapped using the following phase unwrapping algorithm:

where (i, j) and (k, l) denote the adjacent pixel positions, φ_{disp_△t}The phase of the deformation occurring during time interval △ t is acquired for the interference image pair, λ being the radar wavelength.

Preferably, the atmospheric correction is performed on the phase unwrapped coherence map γ by one of three methods to obtain a deformation map of the target region: distance function fitting method, permanent scatterer method and meteorological data calibration method.

Preferably, the geocoding the deformation map of the target area in the radar coordinate system, and projecting the deformation map to the geographic coordinate system to obtain the geocoded deformation map includes:

firstly, parameters of a coordinate conversion model are obtained by selecting homonymous points of a radar image and a topographic map of a monitored target area, the coordinate conversion model is further established, and the radar image is subjected to geographic coordinate conversion by utilizing a polynomial obtained by calculation: the obtained ground-based InSAR earth surface deformation monitoring result is plane grid data, in order to accurately obtain homonymous points, more than 3 corner reflectors are arranged in a monitoring target area, the geodetic coordinates of the monitoring target area are obtained by using a GPS, pixel coordinates corresponding to the corner reflectors are found in radar images, the relation between homonymous points is established, finally a coordinate conversion model is solved, and the result in a radar coordinate system is converted into a geographic coordinate system according to the coordinate conversion model, so that the geocoding is realized.

Corresponding to the above method embodiment, as shown in fig. 2, a schematic structural diagram of a subway subgrade structure monitoring device based on a foundation InSAR according to an embodiment of the present invention is shown, where the device includes:

the image acquisition unit 21 is used for repeatedly observing a target area on the linear scanning slide rail by using the radar sensor, and acquiring a synthetic aperture radar SAR image in about 10 seconds;

the image registration unit 22 is configured to match pixels representing the same ground object in the target region in the two SAR images to the same position, and perform image registration;

an interference generating unit 23 for conjugate multiplying the interference image after the image registration to the imageObtaining an interference phase diagram, and calculating to obtain a corresponding coherence diagram gamma according to the following formula:

a noise filtering unit 24, configured to perform noise filtering processing on the acquired coherence map γ;

a phase unwrapping unit 25 for phase unwrapping the coherence map γ after the noise filtering processing;

an atmospheric correction unit 26, configured to perform atmospheric correction on the coherence map γ subjected to phase unwrapping, and acquire a deformation map of the target region;

and the geocoding unit 27 is configured to geocode the deformation map of the target area in the radar coordinate system, project the deformation map to the geographic coordinate system, and acquire the geocoded deformation map.

Preferably, as shown in fig. 3, which is a schematic diagram of a noise filtering unit according to an embodiment of the present invention, the noise filtering unit 24 includes:

the pre-filtering module 241 is used for repeatedly observing a target area on the linear scanning slide rail by using a radar sensor, and filtering the obtained original SAR image after obtaining a synthetic aperture radar SAR image in about 10 seconds;

a post-filter module 242 for conjugate multiplying the interference image after image registration byAfter obtaining the corresponding coherence map gammaAnd (4) line filtering.

Preferably, the phase unwrapping unit 25 is specifically configured to perform phase unwrapping on the coherence map γ after the noise filtering processing by using the following phase unwrapping algorithm:

Preferably, the atmospheric correction unit 26 is specifically configured to perform atmospheric correction on the phase unwrapped coherence map γ by using one of the following three methods to obtain a deformation map of the target area: distance function fitting method, permanent scatterer method and meteorological data calibration method.

Preferably, the geocoding unit 27 is specifically configured to first obtain parameters of a coordinate transformation model by selecting a same-name point of the radar image and a topographic map of the monitored target area, further establish the coordinate transformation model, and perform geographic coordinate transformation on the radar image by using a polynomial obtained by calculation: the obtained ground-based InSAR earth surface deformation monitoring result is plane grid data, in order to accurately obtain homonymous points, more than 3 corner reflectors are arranged in a monitoring target area, the geodetic coordinates of the monitoring target area are obtained by using a GPS, pixel coordinates corresponding to the corner reflectors are found in radar images, the relation between homonymous points is established, finally a coordinate conversion model is solved, and the result in a radar coordinate system is converted into a geographic coordinate system according to the coordinate conversion model, so that the geocoding is realized.

The following examples illustrate embodiments of the present invention in detail by way of application examples:

the ground-based InSAR system takes the ground, a building or a land vehicle as a platform, can select the optimal observation visual angle according to the monitoring requirement, and selects the observation time base line according to the characteristics of a monitored target, thereby showing good flexibility and operability; the foundation InSAR system is convenient and simple to transport and install, high in operation automation degree and powerful in data processing software function. During work, a sensor does not need to be installed in a target area, and workers do not need to approach or enter the target deformation area, so that the safety of the workers is guaranteed, and the influence on deformation is avoided.

FastGBSAR foundation InSAR system hardware composition

The hardware composition of the foundation InSAR system comprises the following units:

① Radar sensor the core device of the system is a step frequency continuous wave radar, which includes four signal transmitters and receivers and antennas to generate, transmit and receive microwave signals.

② Linear scanning slide rail, which is a carrying platform for repeated measurement of radar sensor, and comprises a 2.5m long aluminum rail, a stepping motor and a position encoder for realizing synthetic aperture radar.

③ energy supply and system control unit, the system supplies energy through two 12V batteries or external 220V AC power supply, the generator can be used to supply power in the observation environment of lack of AC power supply in the field, the system control unit is a notebook computer with control software, the software can set measurement parameters, check the preliminary measurement result and control the system state.

In the operation process, firstly, setting measurement parameters required by operation through a notebook computer, and checking whether the equipment state is normal or not; under the control of the energy supply and data transmission unit, the motor drives the radar sensor to repeatedly observe a target area on the linear scanning slide rail, and one SAR image is obtained in about 10 seconds; meanwhile, the notebook computer can automatically record and store the images acquired by the radar sensor, and the measurement result can be checked through the notebook computer, so that the data quality can be preliminarily evaluated.

System software composition

The software of the foundation InSAR system is combined into Controller data acquisition software and FastGBSAR range data real-time analysis software. The data acquisition software mainly has the functions of parameter setting, power supply control and system state real-time description; the data real-time analysis software can analyze and process the acquired mass data in real time and quickly acquire the monitoring result, can realize the time series analysis of a single point and the whole observation area, and can output the monitoring result to a GIS or other related compatible software.

Operating conditions of foundation InSAR system

(1) And continuously supplying power. In order to ensure long-term continuous monitoring, the foundation InSAR system needs to be powered continuously. The standby battery of the equipment can be maintained for about 22 hours, so that alternating current is adopted for continuous power supply or alternating current and direct current are alternately used in the long-time continuous monitoring process. When in field measurement, the generator is needed to be prepared due to the lack of an alternating current power supply. In summary, the ground-based InSAR survey station should be properly selected closer to the power source to avoid unnecessary trouble.

(2) The traffic is convenient for instrument transportation. The ground-based InSAR system equipment is a precise and expensive instrument, and needs to be handled lightly in the carrying process, and certain measures are taken to ensure the stability of the instrument so as to avoid damaging components. The equipment is bulky and heavy, so that a place where transportation is convenient or where instruments are easy to carry should be selected when selecting the station.

(3) The distance and range are monitored. In actual measurement, the monitoring distance of the foundation InSAR system needs to be controlled within a reasonable range according to the topographic conditions, namely the maximum monitoring distance cannot exceed 4 kilometers, and the maximum coverage range cannot exceed 7 kilometers squared.

(4) And (5) the condition of the full sight. The ground-based InSAR system should work under a clear line of sight condition, and no obstacles can exist between the survey station and the monitoring area. If an obstacle exists, the reflection intensity of the monitored object is affected or even no echo exists, so that the coherence is reduced, and certain difficulty is caused to data processing.

(5) And (5) measuring station stability. During monitoring, the ground-based InSAR system should remain level and not be disturbed. Therefore, whether an instrument mounting point is stable or not is considered when selecting the measuring station, and the instrument mounting point is preferably mounted on stable bedrock, or whether an observation platform is built or not is considered according to the actual condition of an observation area and the requirement of measurement precision.

(6) And (6) radar view angle. Generally, the target object deforms in a three-dimensional space, and the ground-based InSAR system can only obtain the deformation amount in the sight line direction. The angle between the radar observation direction and the target displacement vector determines the sensitivity of the measurement, so a reasonable radar view angle needs to be set so as to obtain a better deformation result. In the monitoring process, the foundation InSAR system is preferably just opposite to the main displacement direction of a target object, the included angle between the radar observation direction and the target displacement vector cannot be too large, and the larger the angle is, the larger the monitoring error is. Therefore, during site selection, the instrument should be debugged for multiple times, the data quality under different viewing angles is compared, and the radar viewing angle with better data quality is selected for observation.

(7) Regional vegetation problems are monitored. In order to obtain a high-precision deformation result, the observation area needs to have a large correlation so as to ensure that the later data processing can be smoothly carried out. Generally, buildings, metals, rocks, and the like have high correlation, and vegetation coverage areas have poor correlation, which will seriously affect the measurement result. So that the vegetation in the interested area is avoided as much as possible during the site selection. If the vegetation coverage of landslide and the like is high, the artificial corner reflector can be properly arranged.

(8) Safety problem

In the working process of the foundation InSAR system, workers should watch on the working point of the instrument all the time, and non-workers are prevented from approaching the instrument or entering the sight range of the radar, so that the instrument is protected and the observation result is not influenced by human factors. In addition, the station monitoring staff is at least more than two persons to ensure the safety.

The FastGBSAR ground InSAR system ensures that the sensor always transmits radar waves with the center frequency of 17.2GHz (Ku wave band) by using frequency modulation continuous waves. The Ku band has a high frequency and is not easily interfered by microwave radiation, so that the Ku band has a long effective transmission distance (up to 4 Km). The bandwidth of the radar sensor of the ground-based InSAR system is 300MHz, and the large bandwidth enables the radar to divide a target area more finely, so that high resolution (0.5m) in a distance direction is realized. Due to the adoption of the synthetic aperture radar technology, the FastGBSAR system can synthesize the real radar antenna aperture with smaller size into a larger equivalent radar antenna aperture by a data processing method, and the angle-direction resolution of measurement is improved. In addition, by comparing the phase information of radar echoes at different moments, the displacement value of the target object in the corresponding time period is obtained by adopting a radar interferometry technology, and the measurement precision can reach 0.1 mm.

Basic principle of foundation InSAR

The basic principle of the ground-based InSAR is the same as that of the satellite-borne and airborne InSAR differential interferometry, phase information provided by SAR complex data is used as an information source, and the acquired SAR image of the target area is subjected to interference processing so as to extract target deformation information. However, the ground-based InSAR system takes the ground, buildings or land vehicles as a platform, the repeated observation period is short, and parameters such as the measurement time interval, the observation visual angle, the observation distance and the like can be flexibly controlled according to the actual observation scene and the measurement requirement in the working process, so that the ground-based InSAR system has certain difference with a satellite-borne or airborne InSAR system in the working mode and data processing. The conventional ground-based InSAR technology integrates multiple technologies such as frequency modulation continuous wave, synthetic aperture radar and interferometry, the distance resolution of the radar is improved by the frequency modulation continuous wave technology, the azimuth resolution of the radar is improved by the synthetic aperture radar technology, the electromagnetic wave phase information of a target point in an image is compared by repeatedly observing the same target area in different time periods, and the submillimeter deformation information of the surface of the target area is acquired by the interferometry.

Frequency modulated continuous wave technique

Frequency modulated continuous wave radar is a radar system that obtains range and velocity information by frequency modulating a continuous wave. Radar frequency modulation can be achieved in a variety of ways, both linear and sinusoidal modulation having been widely used in the past. Among them, the chirp is most diversified, and it is also most suitable for obtaining distance information in a wide range when FFT processing is employed. For this reason, focus problems with frequency modulated continuous waves have been substantially concentrated on chirped continuous wave (LFMCW) radars. The LFMCW radar has the advantages of high distance resolution, low transmitting power, high receiving sensitivity, simple structure and the like, has no distance blind area, has the characteristics of better anti-stealth, background clutter resistance and anti-interference capability than a pulse radar, is particularly suitable for short-distance application, and is rapidly developed in military and civil aspects in recent years.

Synthetic aperture radar technology

The synthetic aperture radar is an active microwave sensor, and acquires a two-dimensional high-resolution slant range image of a target area by transmitting electromagnetic waves to the target area and receiving a target backscattering echo. According to the classification of an observation platform, the synthetic aperture radar can be divided into an airborne type, a satellite type and a foundation type, the radar measures distance and performs two-dimensional imaging according to the motion track of the platform, and two-dimensional coordinate information of the radar is distance information and direction information perpendicular to the distance.

In general, radar resolution is related to pulse width, pulse duration, with narrower pulse widths giving higher resolution. For a real aperture radar, the most direct method for improving the azimuth resolution is to increase the size of an antenna, but the width of the antenna must reach hundreds of meters to improve the resolution from tens of kilometers to a meter, which is obviously difficult to realize in engineering and is not feasible in practical application. Compared with a real aperture radar, the synthetic aperture radar technology breaks through the limitation of the width of a physical antenna, and a signal of a larger and equivalent antenna aperture is virtualized into a signal of the larger and equivalent antenna aperture by utilizing a signal of a smaller real antenna aperture through the relative motion of the radar and a target, so that the azimuth resolution is greatly improved. In the ground-based InSAR measurement, the radar system moves on the horizontal slide rail in a stepping mode, the purpose of synthesizing the aperture is achieved, and the azimuth resolution is improved. Fig. 4 is a schematic diagram illustrating the specific principle of the synthetic aperture radar technology according to the embodiment of the present invention, where P is a ground target, and a1 and a2 are two end points of a sliding rail. When the radar sensor moves from a1 to a2, a doppler shift phenomenon occurs due to the relative movement between the target point and the radar sensor. The azimuth doppler signal is subjected to pulse compression processing by a matched filter, and a synthetic aperture L of a1-a2 is spatially formed:

wherein λ is a radar signal wavelength; d is the antenna aperture; and R is the slant distance from the radar to a target point. At this time, the ground coverage of the equivalent beam is 2L, and the beam width is:

the azimuth resolution is:

as can be seen from the equation (2-3), the azimuth resolution of the synthetic aperture radar is only related to the antenna size D, and is in a proportional relationship, independent of factors such as the slant range and the wavelength. The characteristic shows that the synthetic aperture radar can image the targets at different positions in the observation area with equal resolution, and theoretically, the accuracy of the azimuth resolution can reachHowever, it cannot be considered that the resolution of the azimuth direction can be improved infinitely by reducing D, because in the design of the radar system, if D is too small, the antenna cannot generate a radar beam with sufficient power, and the size of the antenna aperture is subject to many conditions such as the transmission power in the engineering designTo the next step.

Interferometric technique

The ground-based InSAR technology applies the basic principle and method of satellite-borne InSAR to data processing of ground-based radar, so that the deformation of a target area is acquired with high precision. However, there is a great difference between the ground-based InSAR continuous measurement and the satellite-borne InSAR repeated observation. The ground-based SAR is fixed at a certain determined position on the ground, the space baseline of the ground-based SAR is zero, the satellite-borne SAR flies in the space, and the space baseline of the two observations is between dozens of meters and thousands of meters. The data acquisition interval of the ground-based radar system is about several minutes, and the revisit period of the satellite-borne radar system is generally from several days to tens of days. The shortening of the space baseline and the time baseline enables the ground-based radar to acquire higher-quality original data, and reduces the influence of external factors such as atmosphere and the like, thereby improving the interference coherence and further enhancing the interference performance of the SAR image.

In the time interval of two times of measurement of the same area by the radar system, if a certain point changes, the corresponding phase information of the point in the two SAR images is different. The SAR interferometry technology is to calculate the phase difference of the same target in radar images in different time periods so as to obtain the micro deformation value of the target in two periods of time. According to the basic principle of interferometry, the deformation value d and the phase differenceThe relationship of (1) is:

where λ is the radar wavelength. Therefore, on the basis of obtaining the phase difference of each point on the SAR image, the deformation measurement result of the corresponding research area can be calculated by using the formula (2-6). In the process of satellite-borne SAR interferometric processing, the acquired phase difference mainly comprises the following components:

wherein,for the phase of the terrain due to the spatial baseline,the phase of the deformation of the earth surface,in order to be in the phase of the atmospheric disturbance,as noise phase (e.g., speckle noise, thermal noise, etc.). Unlike on-board InSAR, in ground-based InSAR continuous measurements, the spatial baseline is 0, and thusIs 0; meanwhile, the quality of original data acquired by the ground-based radar is high, the influence of noise is relatively small, and the influence of a noise phase can be basically ignored after a proper filtering method is selected. However, in the process of long-time continuous observation, the foundation InSAR is greatly influenced by atmospheric disturbance and needs to be corrected by meteorological simulation or reference point selection correction and other methods. Therefore, for the ground-based SAR interferometry, after data filtering, equation (2-7) can be rewritten as:

differential synthetic Aperture Radar interferometry (D-InSAR) in the InSAR technology mainly uses a two-scene (or multi-scene) repetitive orbit SAR complex image before and after deformation to extract Differential phase information only related to ground deformation (line of sight direction), and can theoretically monitor millimeter-scale deformation after eliminating the influence of topographic factors of interference phases. The foundation InSAR continuous measurement realizes the differential interferometry irrelevant to the terrain, and combines with the Permanent scatterer interferometry (PS-InSAR), thereby greatly improving the deformation monitoring precision. The "two-rail" D-InSAR and PS-InSAR techniques are described below.

D-InSAR technology of one-rail method

The two-orbit method D-InSAR technology is that two scenes of SAR data imaged before and after deformation of a target area are utilized to generate an interference pattern, then DEM data and SAR satellite orbit data of the area are used for simulating a terrain phase, and then the simulated terrain phase is subtracted from the interference phase so as to obtain surface deformation information. The advantage of this method is that it does not require unwrapping of the fringe pattern. The method has the disadvantages that the method is not applicable to an area lacking DEM data, and DEM elevation errors, DEM simulation interference phase errors, registration errors and the like can be introduced when the DEM data are used.

FIG. 5 is a geometric diagram of a two-track differential interferometry measurement according to an embodiment of the present invention. Assuming that P and P' are the positions of the target points before and after deformation respectively, the DEM before deformation and SAR images observed twice can be used for acquiring the deformation phase along the radar visual Line (LOS)

The amount of the target point in the line of sight deformation may be expressed as:

△r＝|R₂|-|R₁| (2-7)

the deformation phase is then:

(II) PS-InSAR technology

The basic principle of the permanent scatterer interferometry is to select a high-coherence point with stable phase information and without being influenced by time and space base line correlation from a group of time sequence SAR images to perform image processing. These point targets may be artificial buildings, bare rock, manually laid corner reflectors, etc. These points are called PS points because they are not affected by noise in time-series images and can maintain stable scattering characteristics for a long time. The main purpose of PS-InSAR is to overcome the effects of spatio-temporal decorrelation and atmospheric delays on SAR image interferometry.

The selection of the PS point is the most critical step in the PS-InSAR technology, and the existing PS point selection methods mainly comprise an average coherence coefficient method, an amplitude dispersion index method and the like. The average coherence coefficient method is to calculate the average coherence coefficient in the time series SAR images and select the pixel which is larger than the selected threshold value as the PS point. The average coherence coefficient method has the advantages that only two SAR images are needed, and has the disadvantages that isolated coherent points are easy to miss-select, and non-coherent points near the coherent points are easy to be mistakenly selected as coherent points. The amplitude dispersion index method is to obtain the amplitude mean value and the standard deviation of each pixel in the time series SAR image, take the quotient of the amplitude mean value and the standard deviation as the amplitude dispersion index, and select the pixel with the amplitude dispersion index smaller than a given threshold value as a PS point. The amplitude dispersion index method is simple in calculation, high in efficiency and free of resolution loss. But it has the disadvantage of requiring a large number of SAR images for statistical analysis.

Foundation InSAR data processing flow

The foundation InSAR system can obtain the deformation result of the target area through a series of interference processing processes. Although the principle is the same as that of satellite-borne or airborne SAR interferometry, the zero-space baseline working mode is adopted and accurate orbit parameters are known, so important steps such as a horizon removing effect and baseline estimation in satellite-borne or airborne InSAR data processing are not considered in data processing. Fig. 6 is a schematic diagram of a process flow of ground-based SAR interferometry data processing according to an embodiment of the present invention, where the process flow mainly includes raw image scaling and focusing, image registration, interferogram generation, filtering, phase unwrapping, atmospheric correction, and geocoding.

2.3.1 image registration

Image registration is one of the key steps of ground-based InSAR data processing, and is to match the pixels representing the same ground object in two images to the same position. The image registration steps are mainly divided into three steps: image matching, affine transformation, and image resampling. In general, the registration process can be done highly automated if the image elements do not vary significantly between images. When the ground-based InSAR system repeatedly observes the same target area, the observation track and the observation visual angle of the ground-based radar are slightly changed due to the slight deviation of the observation platform, so that the image is dislocated and distorted in the distance direction and the azimuth direction (DelVentisette et al.2011). Therefore, image registration is necessary for the discontinuous viewing mode, whereas image registration is usually not necessary for the continuous viewing mode due to the stationary orbit. However, in the case of a long distance and a long observation time, the image is distorted due to atmospheric changes during some image acquisition, and therefore, the partial image should be corrected and compensated.

2.3.2 interferogram generation and Filtering

Conjugate multiplying the registered interference image pairThe interference phase diagram can be obtained, and the corresponding coherence diagram gamma can be obtained by calculation according to the formula (2-9). The coherence map reflects the coherence of an observation region, the coherence is an important parameter for evaluating the interference quality, and the calculation formula is as follows:

gamma is between 0 and 1, and when gamma is equal to 0, the two images are completely irrelevant; when gamma is equal to 1, the two images are the same, the interference coherence is better, and the higher the signal-to-noise ratio of the images is, the more stable the phase center of the scatterer is, and the earth surface object has spatial consistency.

The interferogram is affected by noise introduced by data processing and system noise, and inevitably reduces coherence, which affects subsequent phase unwrapping and data interpretation, so that the noise needs to be filtered (Di Traglia et al 2014). The noise filtering process is divided into pre-filtering and post-filtering, wherein the former is to filter the original SAR image before the generation of the interferogram so as to eliminate or reduce the influence of system noise, and the latter is to filter the original SAR image after the generation of the interferogram so as to eliminate or reduce noise introduced by data processing. And a foundation is laid for subsequent data processing through the processing of pre-filtering and post-filtering. The space baseline in the foundation InSAR continuous observation is zero, so that terrain phase compensation is not needed, the space baseline in a non-continuous observation mode is not zero, an additional terrain phase is introduced, and the terrain phase in an interference pattern needs to be eliminated.

2.3.3 phase unwrapping

Due to the periodicity of the trigonometric function, the phase values of each point in the interferogram fall within the range of the main values [ -pi, pi ], and each phase value must be added by an integer multiple of 2 pi to obtain the true phase value. Phase unwrapping, i.e., the process of recovering the principal value of the interferometric phase to the true phase value, is one of the important links in the ground-based SAR interferometric measurement, and directly affects the precision of deformation measurement. The current phase unwrapping algorithm generally needs to satisfy:

where (i, j) and (k, l) denote the adjacent pixel positions, φ_{disp_△t}The method is characterized in that deformation phase occurring in time interval △ t for acquiring interference image pairs is obtained, and lambda is radar wavelength, dense interference fringes, top-bottom inversion, shadow and coherent noise introduced in the original radar signal processing process and the like caused by large topographic relief generally exist in satellite-borne or airborne InSAR data, so that phase unwrapping of interference data is very difficultThe data acquisition time of the ground-based SAR continuous observation mode is short, and the deformation rate of a target and the time interval △ t of acquisition of two adjacent SAR images can be generally metTherefore, the phase unwrapping is easier and relatively accurate; however, for most discontinuous observation modes, due to the existence of various loss coherence factors, the phase unwrapping difficulty is high and unwrapping errors exist.

2.3.4 atmospheric correction

The signal emitted by the radar is an electromagnetic wave, and during the propagation process of an Atmospheric medium, an uneven medium can disturb a propagation path, so that the propagation direction and the propagation path of the signal are changed, and an Atmospheric Additional Phase (APS) is generated, wherein the influence of the Phase in the process of InSAR data processing is called an Atmospheric effect. Atmospheric effects are one of the major sources of phase error in ground-based SAR interferometry and need to be attenuated or eliminated. Because the measurement time is relatively flexible, the atmospheric disturbance error of the ground-based SAR is different from that of a satellite-borne or airborne system to a certain extent. At present, no scheme for systematically solving the influence of the atmospheric effect exists, and three methods are mainly adopted to reduce the influence of the atmospheric effect: the method comprises a distance function fitting method, a permanent scatterer technology and a meteorological data calibration method. The three methods have respective application ranges and advantages and disadvantages, and are selected in a targeted manner according to observation conditions in practical application.

(1) Distance function fitting method. The distance function fitting method is to select stable points or artificially lay angle reflection points in an observation area and then weaken or eliminate atmospheric influence through the stable points. Generally, the stable point or the arranged angular reflection point is only influenced by the environmental change, and the correction value of the environmental change is obtained through the phase change of the stable point. When the observation area range is small, the atmospheric delay can be considered to be in linear relation with the distance r, namely the formula

In consideration of the deviation in the actual situation, a plurality of stable points are generally used to average a to reduce the atmospheric influence. When the monitoring area is large and the scene is complex, the atmospheric delay is in a nonlinear relation with r, then

In general, a₀Can be omitted, the parameter a can then be obtained by two angular reflection points₁And a₂The value of (c). And obtaining the atmospheric phase through the parameters, and subtracting the atmospheric phase from the interference phase. According to the thermal signal to noise ratio, the estimated signal to noise ratio and the coherence value of the radar image and combining the situation of the solid, stable Points with high thermal signal to noise ratio, high estimated signal to noise ratio and coherence value close to 1 are selected as Ground Control Points (GCP), and then the atmospheric influence is reduced or eliminated through the stable Points.

(2) Permanent diffuser technology. The italian in 2001 proposed the permanent scatterer technique, Ferretti, whose core idea was to perform a time-series interferometric phase analysis on the detected permanent scattering points, and separate and extract the individual phase components from them. According to the analysis of the permanent scattering point phase on the time sequence, each component phase is gradually extracted, so that the error of each component to be solved such as an atmospheric phase, a deformation phase and a terrain residual phase and the reliability of the result are reduced, and the influence of the atmospheric effect in the interference pattern is weakened. In the case where the monitoring area is not large, it can be assumed that the atmospheric phase changes linearly or nonlinearly in both the azimuth direction and the range direction. Noferini analyzes the permanent scattering technique for landslide monitoring and achieves good results. It is worth noting that the atmosphere is not independent in time intervals of less than one day and is time, baseline and space dependent.

(3) And (4) a meteorological data calibration method. The method is an atmospheric refraction model that is dependent on humidity, temperature, air pressure and distance. And simulating the phase according to the atmospheric refraction model by obtaining the atmospheric parameters in the monitoring area so as to compensate the atmospheric phase in the interferogram. Meteorological parameters of a meteorological data correction method are relatively easy to acquire and can be used for eliminating trend atmospheric influences such as weather changes of the atmosphere in a day.

2.3.5 geocoding

In order to combine the ground surface deformation result with the basic geographic data (such as administrative region map, topographic map, line drawing map and the like) and the thematic data (such as hydrogeology and level data) of the monitoring area so as to better analyze the space-time distribution characteristics and the cause of the ground surface deformation, the ground-based InSAR monitoring result needs to be unified with the coordinate system of the basic geographic data and the thematic data of the monitoring area, namely, the result in the radar coordinate system needs to be projected under the geographic coordinate system. The method comprises the steps that a ground InSAR obtains one-dimensional deformation of a radar visual line, a coordinate system of a result is a plane rectangular coordinate system which takes a radar position as an original point, a radar azimuth direction as an x axis and a radar distance direction as a y axis, and the radar visual line is projected to a geographical coordinate system through coordinate conversion.

The premise of coordinate transformation is that a proper coordinate transformation model is selected, firstly, parameters of the coordinate transformation model are solved by selecting homonymous points of the radar image and the topographic map of the monitored area, the coordinate transformation model is further established, and the radar image is subjected to geographic coordinate transformation by utilizing a polynomial obtained through calculation. The obtained ground-based InSAR earth surface deformation monitoring result is plane grid data, in order to accurately obtain homonymous points, more than 3 corner reflectors are distributed in a monitoring area, the geodetic coordinates of the ground-based InSAR earth surface deformation monitoring result are obtained by using a GPS, pixel coordinates corresponding to the corner reflectors are found in radar images, the relation between homonymous points is established, finally a coordinate conversion model is solved, and the result in a radar coordinate system is converted into a geographic coordinate system according to the coordinate conversion model, so that the geocoding is realized.

Influence factor of foundation InSAR measurement accuracy

The theoretical precision of ground InSAR deformation monitoring reaches submillimeter level, and for such high-precision deformation monitoring, tiny errors can cause great influence to the measurement precision. The ground-based InSAR system has a special working mode and system performance, so that the ground-based InSAR system has a signal analysis model and error characteristics different from those of a satellite-borne or airborne system when deformation monitoring is carried out by applying the ground-based InSAR. The key factors influencing the measurement accuracy of the foundation InSAR system comprise atmospheric effect influence, target scatterer time decorrelation, system observation platform stability, system working frequency stability and the like. Factors influencing the measurement accuracy of the ground-based InSAR are analyzed in detail in the aspects of a radar system, a data acquisition process and data processing.

(1) Interfering with the phase error. The interference phase error is the main source of the line-of-sight deformation error in the foundation InSAR measurement. The interference phase error is influenced by factors such as changes in atmospheric conditions during observation, changes in scattering characteristics of the target, stability of the system phase, phase unwrapping errors, and noise. Atmospheric effect influences are important sources of interference phase errors and are also important and difficult points in data processing of ground-based InSAR measurement. The scattering coefficient of the target is determined by the shape and texture characteristics of the target (surface feature targets such as metal, rock, vegetation, sand, etc.), and the characteristics of the target such as roughness and humidity. In the ground-based InSAR measurement, the scattering characteristics of targets in two previous and next measurements are generally considered to be very similar, so that the scattering phase difference of the targets in the measurement can be ignored, but if the two previous and next observations are long in time interval, the scattering characteristics of the target region can be greatly changed. The stability of the system phase is mainly influenced by the stability of the reference local oscillator and the change of the signal transmission path between the transmitting antenna and the receiving antenna and the system, and the influence can be eliminated or weakened by designing a stable radar system and a corresponding correction technology. Phase unwrapping is a difficult point in data processing of foundation InSAR measurement, when continuous observation is carried out and the radar revisiting period is short, due to the fact that the time interval between the two previous observation and the two subsequent observation is short, coherence between the obtained adjacent images is good, and the problem of phase unwrapping generally does not exist unless a target moves fast in an incoherent mode. When a radar revisit period is long, under the influence of time, space decorrelation and noise, a strong coherent region in an observation region is sparse, the area of the strong coherent region is small, accurate phase unwrapping of the whole observation region is difficult, and phase unwrapping research under the condition is lacked in existing foundation InSAR measurement related documents. The effects of noise can be suppressed by filtering and subsequent signal processing.

(2) And observing the stability of the platform. The ground-based InSAR system takes the ground, buildings or land vehicles as an observation platform, and the instability of the ground-based InSAR system mainly appears in two forms: firstly, the settlement of the ground where the observation platform is located causes the instability of the foundation InSAR system; and secondly, instability is caused by the insecure fixing device between the foundation InSAR system and the observation platform. The observation platform of the foundation InSAR system can change the radar observation orbit and the visual angle as long as the small offset occurs, so that the coherence of an interferogram is influenced, and the measurement precision is reduced finally. Especially for long-term observation, instability of the observation platform will be a serious problem. The deviation of the observation platform can cause millimeter-scale errors on the measurement precision of the foundation InSAR system, and the influence of the millimeter-scale errors can be reduced by a high-precision image registration method.

(3) Stability of the operating frequency of the system. The stability of the system working frequency is also one of the factors influencing the accuracy of the ground-based SAR interferometry. The line-of-sight distortion measurement error produced by the frequency offset is a function of the frequency offset ratio and the target slope distance. The distortion error of the equivalent line of sight, which may be caused by a frequency error below ten-thousandth, is in the order of millimeter, and the error becomes larger with the increase of the distance. The conventional foundation InSAR system has high frequency stability and small frequency deviation in a short time, for example, the Ku wave band of the FastGBSAR foundation InSAR system has high frequency, is not easy to be interfered by microwave radiation, and can ensure that the sensor always emits radar waves with the frequency of 17.2GHz (Ku wave band). Therefore, the influence of the instability of the system frequency on the measurement precision can be avoided when short-time measurement is carried out; however, when a long-time continuous deformation monitoring task is performed, the tiny frequency offset of the system will gradually accumulate and continuously expand along with time, so that a corresponding correction technology needs to be considered during system design, for example, a frequency-division multi-stage correction mechanism is utilized, a reference channel is set, and an intermediate frequency receiver technology is adopted to ensure that the system has good phase-frequency characteristics, and deformation measurement errors caused by frequency instability can be estimated and then compensated in a data processing process.

As can be seen from the above analysis, when high-precision differential interferometry is implemented using the ground-based InSAR system, the influence of each factor must be sufficiently considered. The high-precision registration, the accurate atmospheric correction and the phase unwrapping of the complex image of the ground-based SAR are the key problems to be further and deeply researched and solved in the influence factors of the interference measurement precision of the ground-based SAR at present.

Operating conditions of foundation InSAR system

(8) Safety problem

A FastGBSAR foundation InSAR system is adopted to carry out long-time monitoring on the track and the roadbed of the No. 13 line north aster road construction section of the subway from 10 months 7 days to 11 months 6 days in 2016, and each observation is a half-hour continuous observation. During monitoring, the ground-based InSAR system should remain level and not be disturbed. Therefore, whether the instrument mounting point is stable or not needs to be considered when selecting the measuring station, and the instrument mounting point is preferably mounted on a stable bedrock. In addition, the ground-based InSAR system should operate in a clear line of sight condition, with no obstructions between the survey station and the monitored area. If an obstacle exists, the reflection intensity of the monitored object is affected or even no echo exists, and finally the coherence is reduced, so that certain difficulty is caused to data processing.

In consideration of the special requirements of the survey station of the foundation InSAR system, in order to select a proper survey station, project groups carry out site survey outside the influence range of subway construction. Because the deformation monitoring result obtained by the foundation InSAR system is the deformation of the target point along the radar visual line, if the settlement observation of the subway rail and the roadbed is required, the instrument needs to be arranged at a high position, and the radar needs to be adjusted to be in an overlooking state. Through site reconnaissance, it is difficult to find a monitoring position whose field of view completely meets the settlement observation condition. If the foundation InSAR is arranged at the top of the building, on one hand, the safety of workers and instruments cannot be guaranteed, and on the other hand, the continuous power supply of the instruments is not facilitated. In addition, the problems of convenience and the like of instrument transportation and personnel attendance need to be considered when the station is selected.

On the premise that field conditions cannot meet foundation InSAR settlement observation, factors in all aspects are considered comprehensively, and the foundation InSAR is adopted in the project to monitor the transverse deformation of the subway track structure and the transverse deformation of the roadbed structure (the transverse deformation is also an important parameter of subway deformation). Finally, the instrument is arranged at 65m north of the construction section rail and roadbed.

The bandwidth of the radar sensor of the FastGBSAR system is 300MHz, and the large bandwidth enables the radar to divide a target area more finely, so that high resolution (0.5m) in a distance direction is realized. Due to the adoption of the synthetic aperture radar technology, the FastGBSAR system can synthesize the real radar antenna aperture with smaller size into a larger equivalent radar antenna aperture by a data processing method, and the angle-direction resolution of measurement is improved. In addition, by comparing the phase information of radar echoes at different moments, the displacement value of the target object in the corresponding time period is obtained by adopting a radar interferometry technology, and the measurement precision can reach 0.1 mm. The main technical parameters of the FastGBSAR ground-based InSAR system are shown in table 1. Through instrument debugging, the proper observation direction is finally determined by combining the reflection intensity condition of the radar echo signal, and the elevation angle of the radar is adjusted to 15 degrees by utilizing the elevation adjuster of the radar host.

TABLE 1 main technical parameters of FastGBSAR Foundation InSAR System

FIG. 7 is a graph showing the reflection intensity of a target signal according to an exemplary embodiment of the present invention; FIG. 8 is a diagram of a deformation time sequence of monitoring points according to an embodiment of the present invention; through the experiment of ground base InSAR monitoring Beijing subway No. 13 line Beiyuan road construction section track structure and roadbed structure, can draw the conclusion: and manually monitoring the transverse deformation accumulated values of the track structure and the roadbed structure between the 13 # line north garden station-vertical water bridge station of the subway after line recovery to be within 0.52mm (the control value is 2.0mm), and knowing that the track structure and the roadbed structure in the target area are in a stable state in the horizontal direction according to the track horizontal control value obtained by an evaluation unit. During the test, the rainfall lasts for more than 24 hours, and under the severe observation condition, the radar still obtains a high-precision deformation field of a space-time continuous target area, so that important basic data are provided for further quantitative research on subway track deformation, the feasibility and the reliability of the foundation InSAR in subway deformation monitoring are verified, and the huge research value and the application prospect in deformation monitoring are realized.

The test is the first time that the ground-based InSAR monitoring technology is applied to subway deformation monitoring in China, a new monitoring means is developed for urban rail transit deformation monitoring and railway deformation monitoring, full-automatic deformation monitoring service can be realized by adopting the technology, and manpower resources and material cost are greatly saved.

The embodiment of the invention can realize the following purposes:

It should be understood that the specific order or hierarchy of steps in the processes disclosed is an example of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged without departing from the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order, and are not intended to be limited to the specific order or hierarchy presented.

In the foregoing detailed description, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the subject matter require more features than are expressly recited in each claim. Rather, as the following claims reflect, invention lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. To those skilled in the art; various modifications to these embodiments will be readily apparent, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

What has been described above includes examples of one or more embodiments. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the aforementioned embodiments, but one of ordinary skill in the art may recognize that many further combinations and permutations of various embodiments are possible. Accordingly, the embodiments described herein are intended to embrace all such alterations, modifications and variations that fall within the scope of the appended claims. Furthermore, to the extent that the term "includes" is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term "comprising" as "comprising" is interpreted when employed as a transitional word in a claim. Furthermore, any use of the term "or" in the specification of the claims is intended to mean a "non-exclusive or".

Those of skill in the art will further appreciate that the various illustrative logical blocks, units, and steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate the interchangeability of hardware and software, various illustrative components, elements, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design requirements of the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present embodiments.

The various illustrative logical blocks, or elements, described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor, an Application Specific Integrated Circuit (ASIC), a field programmable gate array or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a digital signal processor and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a digital signal processor core, or any other similar configuration.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may be stored in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. For example, a storage medium may be coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC, which may be located in a user terminal. In the alternative, the processor and the storage medium may reside in different components in a user terminal.

In one or more exemplary designs, the functions described above in connection with the embodiments of the invention may be implemented in hardware, software, firmware, or any combination of the three. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media that facilitate transfer of a computer program from one place to another. Storage media may be any available media that can be accessed by a general purpose or special purpose computer. For example, such computer-readable media can include, but is not limited to, RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store program code in the form of instructions or data structures and which can be read by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Additionally, any connection is properly termed a computer-readable medium, and, thus, is included if the software is transmitted from a website, server, or other remote source via a coaxial cable, fiber optic cable, twisted pair, Digital Subscriber Line (DSL), or wirelessly, e.g., infrared, radio, and microwave. Such discs (disk) and disks (disc) include compact disks, laser disks, optical disks, DVDs, floppy disks and blu-ray disks where disks usually reproduce data magnetically, while disks usually reproduce data optically with lasers. Combinations of the above may also be included in the computer-readable medium.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A subway subgrade structure monitoring method based on foundation InSAR is characterized by comprising the following steps:

carrying out noise filtering processing on the obtained coherence map gamma;

2. The method for monitoring the subgrade structure of the subway based on the foundation InSAR as claimed in claim 1, wherein the radar sensor is used for repeatedly observing the target area on the linear scanning slide rail, and after a synthetic aperture radar SAR image is obtained in about 10 seconds, the obtained original SAR image is filtered;

3. The method for monitoring the subway subgrade structure based on the foundation InSAR as claimed in claim 1, wherein the coherent graph γ after the noise filtering is performed is subjected to phase unwrapping by using the following phase unwrapping algorithm:

where (i, j) and (k, l) denote the adjacent pixel positions, φ_{disp_Δt}The phase of the deformation occurring within a time interval Δ t is acquired for the interference image pair, λ being the radar wavelength.

4. A subway roadbed structure monitoring method based on ground-based InSAR as claimed in claim 1, characterized in that, atmospheric correction is carried out to the coherent map γ for phase unwrapping by one of the following three methods to obtain the deformation map of said target area: distance function fitting method, permanent scatterer method and meteorological data calibration method.

5. The method for monitoring the subway subgrade structure based on the foundation InSAR as claimed in claim 1, wherein said geocoding is performed on the deformation map of the target area under the radar coordinate system, and the deformation map after geocoding is obtained by projecting the deformation map under the geographic coordinate system, which comprises:

6. A subway roadbed structure monitoring device based on foundation InSAR is characterized in that the device comprises:

7. The subway roadbed structure monitoring device based on the foundation InSAR, as claimed in claim 6, wherein the noise filtering unit comprises:

the pre-filtering module is used for repeatedly observing a target area on the linear scanning slide rail by using the radar sensor, and filtering the obtained original SAR image after obtaining a synthetic aperture radar SAR image in about 10 seconds;

a post-filter module for conjugate multiplying the interference image after image registrationAnd filtering after obtaining a corresponding coherence map gamma.

8. The subway roadbed structure monitoring device based on the foundation InSAR as claimed in claim 6, wherein the phase unwrapping unit is specifically configured to perform phase unwrapping on the coherence map γ after the noise filtering processing by using the following phase unwrapping algorithm:

9. The apparatus according to claim 6, wherein the atmospheric correction unit is specifically configured to perform atmospheric correction on the phase unwrapped coherence map γ by using one of the following three methods to obtain the deformation map of the target area: distance function fitting method, permanent scatterer method and meteorological data calibration method.

10. The subway subgrade structure monitoring device based on the foundation InSAR as claimed in claim 6, wherein said geocoding unit is specifically configured to first select the same-name points of the radar image and the monitored target area topographic map to find the parameters of the coordinate transformation model, further establish the coordinate transformation model, and perform the geographic coordinate transformation on the radar image by using the polynomial obtained by calculation: the obtained ground-based InSAR earth surface deformation monitoring result is plane grid data, in order to accurately obtain homonymous points, more than 3 corner reflectors are arranged in a monitoring target area, the geodetic coordinates of the monitoring target area are obtained by using a GPS, pixel coordinates corresponding to the corner reflectors are found in radar images, the relation between homonymous points is established, finally a coordinate conversion model is solved, and the result in a radar coordinate system is converted into a geographic coordinate system according to the coordinate conversion model, so that the geocoding is realized.