CN118817031B

CN118817031B - A GNSS-R water surface height measurement method for complex situations

Info

Publication number: CN118817031B
Application number: CN202410806577.5A
Authority: CN
Inventors: 赵一沣; 王敏; 于超; 凌凯峰
Original assignee: Wuxi Kalman Navigation Technology Co ltd; Wuxi Kalman Navigation Technology Co ltd Nanjing Technology Center
Current assignee: Wuxi Kalman Navigation Technology Co ltd; Wuxi Kalman Navigation Technology Co ltd Nanjing Technology Center
Priority date: 2024-06-21
Filing date: 2024-06-21
Publication date: 2025-04-18
Anticipated expiration: 2044-06-21
Also published as: CN118817031A

Abstract

The present invention relates to a GNSS-R water surface height measurement method for complex situations, comprising the following steps: GNSS-R data reception; time matching; GNSS-R solution; determination of water surface height and satellite signal elevation angle and azimuth angle screening range. The present invention uses the delayed Doppler method to analyze the properties around the reflection point, distinguishes water bodies from soil vegetation, determines the location of soil vegetation by establishing a model, and then determines whether the location of the reflection point coordinates is located in the soil vegetation area, and records its azimuth and elevation angle, and finally obtains the correct elevation angle and azimuth angle screening range, thereby improving the accuracy of the water surface height solution result; and also establishes the relationship between water level height and elevation angle screening by repeatedly recording the elevation angle and azimuth angle screening range under different water surface heights of the same reservoir, the elevation angle screening range is large when the water level is low, and the elevation angle screening range is small when the water level is high, and different elevation angle screening ranges are selected according to the water surface height solved during the time period, thereby further improving the accuracy of the water surface height solution.

Description

GNSS-R water surface height measurement method aiming at complex situation

Technical Field

The invention relates to the field of surveying and mapping science and technology, in particular to a GNSS-R water surface height measurement method aiming at complex situations.

Background

Nowadays, the global climate is affected, and flood disasters and waterlogging disasters are caused by untimely drainage due to special reasons such as heavy rainfall, storm surge and the like, so that land, houses and the like are waterlogged to cause disasters caused by flooding. In order to minimize loss and protect life and property safety of people, accurate and real-time water level monitoring is important in flood disasters, early warning can be performed in advance, and decision makers can be helped to take emergency measures.

The traditional water level monitoring method mainly comprises a contact type method and a non-contact type method. However, the conventional water level monitoring method has some limitations and disadvantages in practical application, such as that the contact method needs to be in direct contact with the water surface and is easily affected by pollutants or organisms to adhere to the water surface to cause errors or damage, the non-contact method needs to emit electromagnetic waves or sound waves to possibly cause interference or pollution to the surrounding environment, and in addition, the conventional method can only monitor the water level change of a single point or a local area and cannot realize continuous monitoring in a large range or the whole world.

With the intensive research of GNSS, the GNSS-R technology for measuring the reflection of the global satellite navigation system is derived to be applied to water level monitoring, and compared with the traditional water level monitoring method, the GNSS-R water level monitoring technology has the advantages of low cost, low power consumption, all weather, long-term continuity, stability, no need of calibration, high time resolution and wide coverage range. In addition, since GNSS can provide accurate position information, GNSS-R technology can realize the monitoring of the change of the absolute height of the water surface. However, according to the current research and analysis, for GNSS-R water surface monitoring, the water surface height result is easily influenced by non-water surface such as soil vegetation reflection signals, so that the accuracy of a calculation result is reduced, when a height angle azimuth angle screening method is adopted to remove satellite signals in the direction of the soil vegetation, the height angle range screening is often required to be manually configured according to the site situation, the cost is high, the difficulty is high, for reservoir application situations, the water level can be greatly changed, when the water level is low, the water level is exposed out of the water surface, and the satellite signals are reflected by the reservoir wall, so that the positioning accuracy is influenced.

Disclosure of Invention

In view of the foregoing drawbacks of the prior art, it is an object of the present invention to provide a method for GNSS-R water level altimetry for complex situations, which solves one or more of the problems of the prior art.

In order to achieve the above purpose, the technical scheme of the invention is as follows:

the GNSS-R water surface height measurement method for the complex situation is characterized by comprising the following steps of:

receiving GNSS-R data;

time matching;

GNSS-R solution;

and determining the water surface height, the satellite signal altitude angle and the azimuth angle screening range.

Further, the GNSS data reception includes the steps of:

receiving GNSS signals through an upper looking antenna and a lower looking antenna of a GNSS receiver;

Analyzing GNSS signal data;

eliminating the GNSS satellite signals which do not reach the standard in the data set, and completing the construction of a GNSS basic data set;

and solving GNSS-R signal data.

Further, the time matching includes the steps of:

storing the received up-looking antenna data or down-looking antenna data;

and (3) comparing the time with the existing up-looking antenna data or down-looking antenna data, if the time is the same, entering into resolving, if the time is different, removing the data with earlier time, and storing the data which are not removed and waiting for new data to be input.

Further, the GNSS-R solution includes the steps of:

Carrying out water surface height calculation;

Delay-doppler analysis is performed.

Further, the water surface height calculation includes the steps of:

performing GNSS dual-antenna water level monitoring;

Calculating a delay path Deltaρ between the up-looking signal and the down-looking signal;

calculating the height h between the position of the water antenna and the horizontal plane;

and calculating satellite signal reflection point coordinates.

Further, the delay-doppler analysis comprises the steps of:

establishing a reflection point coordinate system;

defining a relation expression of a reflecting point coordinate system and a delay Doppler domain;

Defining a mapping relation model of coordinates of a reflecting point coordinate system and corresponding delay increment and Doppler frequency shift;

and determining reflection point position information.

Further, the relational expression defining the coordinate system of the reflection point and the delay Doppler domain is shown as follows:

Wherein (x, y) is the coordinate of a reflecting point coordinate system, (tau _xy,f_d,xy) is the delay increment and Doppler frequency shift corresponding to the reflecting point, gamma is the elevation angle of the GNSS satellite, h is the height from the receiving antenna to the reflecting surface, Is the GNSS satellite speed.

Further, the mapping relation model of the coordinates of the defined reflection point coordinate system and the corresponding delay increment and Doppler frequency shift is shown as the following formula:

Wherein (x, y) is the coordinate of a reflecting point coordinate system, (tau _xy,f_d,xy) is the delay increment and Doppler frequency shift corresponding to the reflecting point, gamma is the elevation angle of the GNSS satellite, h is the height from the receiving antenna to the reflecting surface, For GNSS satellite velocity, (X _i,Y_i) is the mapping function.

Further, the determining of the water surface height and satellite signal altitude angle and azimuth angle screening range comprises the following steps:

Determining azimuth angles and altitude angles of the non-water surface reflection points;

Judging azimuth angles and altitude angles of satellite signal screening, if the satellite signal screening azimuth angles and the altitude angles meet the rejection conditions, rejecting, and if the satellite signal screening azimuth angles and the altitude angles do not meet the rejection conditions, recording the signal data;

And establishing a screening range of the water surface height and azimuth angle height angle.

Furthermore, the rejection condition is to reject satellite signals with the azimuth angle of the non-water surface reflection point and the altitude angle being smaller than the altitude angle of the point within the range of about 1 DEG of the azimuth angle of the point by taking the azimuth angle and the altitude angle of the non-water surface reflection point as boundaries.

Compared with the prior art, the invention has the following beneficial technical effects:

According to the invention, the properties around the reflection points are analyzed by a delay Doppler method, the water body and the soil vegetation are distinguished, the position of the soil vegetation is determined by establishing a model, whether the position of the coordinates of the reflection points is positioned in a soil vegetation area or not is determined by establishing a model, the azimuth angle and the altitude angle are recorded, the correct altitude angle and azimuth angle screening range are finally obtained, and the accuracy of the water surface altitude calculation result is improved.

And secondly, the invention establishes the screening relation between the water level height and the height angle by repeatedly recording the height angle and the azimuth angle screening range of the same reservoir under different water levels, wherein the height angle screening range is large when the water level is low, the height angle screening range is small when the water level is high, and the different height angle screening ranges are selected according to the water level of the time interval solution, so that the resolving precision of the water level is improved.

Drawings

FIG. 1 shows an overall flow diagram of a GNSS-R water surface altimeter method for complex situations according to an embodiment of the present invention.

FIG. 2 is a detailed flow chart of a GNSS-R water surface altimeter method for complex situations according to an embodiment of the invention.

FIG. 3 shows a schematic diagram of dual antenna water level monitoring for a complex GNSS-R water level altimeter method according to an embodiment of the invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the following provides a detailed description of a method for measuring the height of a GNSS-R water surface according to a complex situation with reference to the accompanying drawings and detailed description. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the drawings are in a very simplified form and are all to a non-precise scale, merely for the purpose of facilitating and clearly aiding in the description of embodiments of the invention. For a better understanding of the invention with objects, features and advantages, refer to the drawings. It should be understood that the structures, proportions, sizes, etc. shown in the drawings are for illustration purposes only and should not be construed as limiting the invention to the extent that any modifications, changes in the proportions, or adjustments of the sizes of structures, proportions, or otherwise, used in the practice of the invention, are included in the spirit and scope of the invention which is otherwise, without departing from the spirit or essential characteristics thereof.

Referring to fig. 1 and 2, a method for measuring the height of a GNSS-R water surface for a complex situation is characterized by comprising the following steps:

And step 1, GNSS-R data reception.

And 1.1, receiving GNSS signals through an up-looking antenna and a down-looking antenna of the GNSS receiver, wherein a direct antenna, namely the up-looking antenna, of the GNSS receiver is taken as a reference station, and a reflecting antenna, namely the down-looking antenna, is taken as a mobile station.

And 1.2, analyzing GNSS signal data, namely obtaining elevation angle (ele), carrier-to-noise ratio (C/N ⁰), azimuth angle (az) and pseudo-range error of the pseudo-range of the satellite signal through analysis.

Further, an inverted pseudo-range ρ ^t is obtained given the receiver position (x _t,y_t,z_t), expressed as shown in equation 1 below:

Wherein: For the clock-difference that the receiver has solved, For correction of satellite clock difference, I is ionospheric delay obtained by Klobuchar model, T is tropospheric delay obtained by Saastamoinen model, c is speed of light, (x _t,y_t,z_t) is receiver coordinates, (x _s,y_s,z_s) is satellite coordinates.

Further, by actually receiving the pseudo-range ρ and inverting the obtained pseudo-range ρ ^t, the pseudo-range error Δρ can be represented by the following formula 2:

Wherein: And The residuals of receiver clock and satellite clock are represented respectively, Δi and Δt represent the ionospheric delay not obtained by the Klobuchar model and the tropospheric delay not obtained by the Saastamoinen model, respectively, epsilon being noise.

And 1.3, eliminating GNSS satellite signals with satellite elevation angles and carrier-to-noise ratios in the data set not reaching standards, and completing construction of a GNSS basic data set.

And 1.4, solving GNSS-R signal data.

Further, the direct antenna, the reflected antenna and the dual-channel software receiver form a receiving system. The direct antenna is a right-hand circularly polarized antenna, and receives GNSS signals from satellites as references. The reflection antenna is a left-hand circularly polarized antenna, faces the water surface and receives GNSS signals reflected by the water surface.

Further, the direct Beidou navigation signal is shown in the following formula 3:

Wherein S is satellite signal, t is time, f is signal frequency, j is satellite number, A is antenna correlation coefficient, C is C/A code, and D is data code.

Further, the Beidou navigation signal reflected by the water surface is shown in the following formula 4:

Where τ is the delay signal, τ=s/c, S is the distance the reflected signal has to travel, c is the speed of light, j is the satellite signal, S is the satellite signal, t is the time, and f is the signal frequency.

Further, the distance s of the reflected signal from the multiple path can be obtained by the phase difference ψ _d ^j between the reflected signal and the direct signal, as shown in the following equation 5:

And 2, time matching. After the GNSS data is received, the data of the direct antenna and the reflected antenna are subjected to time matching, and direct signals and reflected signals with the same time enter a resolving program.

And 2.1, storing the received upward-looking antenna data or downward-looking antenna data, namely storing the received direct antenna data or reflected antenna data each time the received data is received.

And 2.2, performing time comparison with the existing reflection antenna data or direct antenna data, namely, performing time comparison between the direct antenna data and the reflection antenna data. If the time is the same, the calculation is carried out, and if the time is different, the data with earlier time in the two are rejected, and the other data are stored to wait for new data input.

And 3, GNSS-R calculation.

And 3.1, carrying out water surface height calculation.

Step 3.1.1 GNSS dual antenna water level monitoring with continued reference to FIG. 3, it can be seen that the reflected signal received by the water antenna has an additional propagation path compared to the direct signal received by the antenna. The water antenna can thus also be regarded as a virtual antenna located below the water surface and the distance from the virtual antenna to the water surface is equal to the distance from the water antenna to the water surface. When the water level changes, the additional propagation path of the reflected signal changes, and the position of the virtual antenna changes.

Step 3.1.2 calculating the delay path Δρ between the top looking signal and the bottom looking signal when the receiving platform is at a relatively low ground level, it can be assumed that the earth's local is flat. This is highly dependent on the angle of incidence observed and the tolerance of the user to errors caused by this assumption. Errors generated in the vertical component of the specular point position are shown in the case where the earth is assumed to be flat, as compared to the case where the earth is assumed to be spherical. Only angles of incidence up to 50 are included, beyond which the error increases rapidly. The delay path between the direct signal and the reflected signal under this assumption can be expressed as shown in equation 6 below:

△ρ=(2h+s)sinθ(6)

Step 3.1.3, calculating the height h between the position of the water antenna and the horizontal plane, wherein the height between the position of the water antenna and the horizontal plane can be expressed as the following formula 7:

Wherein Deltaρ is a delay path, h is the height from the phase center of the water antenna to the water surface, s is the distance between the two antenna phase center lines, and θ is the satellite height angle at the specular reflection point.

Further, by knowing the position of the receiver with accuracy, the height of the water surface relative to a reference surface, such as an ellipsoid, ground level or other terrain model, can be obtained.

And 3.1.4, calculating satellite signal reflection point coordinates. The satellite azimuth angle ψ and altitude angle θ, and the look-up antenna coordinates (x, y, z) are known by the water level h. The water surface reflection is considered to be specular reflection, and satellite signal reflection point coordinates (x _i,y_i,z_i) can be obtained through a geometric method, as shown in the following formula 8:

(x_i,y_i,z_i)=(x,y,z)+(hcotθsinψ,hcotθcosψ,h)×R(8)

Wherein R is a coordinate system conversion matrix.

And 3.2, performing delay Doppler analysis. Forward scattering of the reflected signal at sea level mainly comprises specular reflection or diffuse scattering, and due to the roughness of the reflecting surface, the characteristics of the reflected signal are complex, which are manifested by attenuation of the signal amplitude and superposition of different time delays and different doppler signals. The interval between the delay lines may be defined as an equal delay zone, where the signal delays are the same. The different delay and doppler in turn correspond to different reflective elements of the reflective surface, and the delay-doppler plot allows accurate quantification of the reflective characteristics of each element area, both in terms of delay and frequency. The reflection intensity of the different reflection surface units is described by a delay-doppler image, the maximum value of the amplitude of which can be used to describe the reflectivity of the reflection medium to the GNSS reflection signal, and the time delay of the two-dimensional correlation value of which can be used to describe the path delay relation of the reflection signal relative to the direct signal, while the reflection surface of the different reflection object directly determines the delay relation.

And 3.2.1, establishing a reflection point coordinate system, namely establishing a space rectangular coordinate system by taking a plane which is perpendicular to a reflection normal line and passes through the reflection point as an xoy plane, taking projection of a signal incident line on the plane as a y axis and taking the reflection normal line as a z axis, and can be called as the reflection point coordinate system.

Step 3.2.2 the relational expression defining the reflection point coordinate system and the delay-doppler domain is shown in the following formulas 9 and 10:

Wherein (x, y) is the coordinate of the reflecting point coordinate system, (τ _xy,f_d,xy) is the delay increment and Doppler frequency shift corresponding to the reflecting point, gamma is the elevation angle of the GNSS satellite, h is the height from the receiving antenna to the reflecting surface, which can be obtained by the angle of the dam body, the height of the antenna and the distance from the antenna to the bottom end of the dam body, Is the GNSS satellite speed.

Step 3.2.3 defining a mapping relation model of coordinates of a reflecting point coordinate system and corresponding delay increment and Doppler frequency shift as shown in the following formula 11:

Wherein (x, y) is the coordinate of the reflecting point coordinate system, (τ _xy,f_d,xy) is the delay increment and Doppler frequency shift corresponding to the reflecting point, gamma is the elevation angle of the GNSS satellite, h is the height from the receiving antenna to the reflecting surface, For GNSS satellite velocity, (X _i,Y_i) is the mapping function.

And 3.2.4, determining the position information of the reflection point, namely projecting the soil vegetation information around the reflection point on the reflection surface after mapping, so as to determine whether the reflection point is the water surface.

And 4, determining the screening range of the water surface height, the satellite signal height angle and the azimuth angle.

And 4.1, determining the non-water surface reflection point and the azimuth angle and the altitude angle of the non-water surface reflection point, wherein when the coordinates of the reflection point are calculated through delay Doppler, the information of the reflection surfaces around the reflection point is obtained at the same time. On one hand, a three-dimensional model is built through the coordinates of the reflection points, the azimuth angle of satellite signal screening is set through the model condition, and on the other hand, the three-dimensional model is compared with the water surface part through the material information of the reflection points and surrounding reflection surfaces, so that soil vegetation and the water surface are distinguished, and the position of the edge of the water surface is determined in an auxiliary mode.

And 4.2, judging azimuth angles and altitude angles of satellite signal screening, if the satellite signal screening azimuth angles and the altitude angles meet the rejection conditions, rejecting, and if the satellite signal screening azimuth angles and the altitude angles do not meet the rejection conditions, recording the signal data.

Furthermore, the rejection condition is to reject satellite signals with the azimuth angle and the altitude angle of the non-water surface reflection point as boundaries, wherein the satellite signals are within about 1 DEG of the azimuth angle of the non-water surface reflection point, and the altitude angle is smaller than the altitude angle of the non-water surface reflection point.

And 4.3, establishing a water surface height and azimuth angle height angle screening range, namely, again carrying out water surface height calculation, recording the relationship between the water surface height and the azimuth angle height angle screening range at the moment, when the water surface height changes by more than 5-10 m, determining the first azimuth angle and the height angle screening range according to the changed water surface condition, recording the corresponding relationship between the azimuth angle and the height angle screening range and the water surface height in an hour unit, and establishing a model. And then the height angle screening range can be timely adjusted through the implemented water surface height condition and model.

The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.

The above examples illustrate only a few embodiments of the invention, which are described in detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.

Claims

1. The GNSS-R water surface height measurement method for the complex situation is characterized by comprising the following steps of GNSS-R data receiving, including the following steps:

The GNSS signals are received through an up-looking antenna and a down-looking antenna of the GNSS receiver,

The data of the GNSS signals are parsed and,

Eliminating the GNSS satellite signals which do not reach the standard in the data set, completing the construction of the GNSS basic data set,

Solving GNSS-R signal data;

Time matching, comprising the following steps:

Stores the received up-looking antenna data or down-looking antenna data,

Comparing the time with the existing up-looking antenna data or down-looking antenna data, if the time is the same, entering into resolving, if the time is different, removing the data with earlier time, and storing the data which is not removed and waiting for new data input;

GNSS-R solution;

The method for determining the screening range of the water surface height and the satellite signal altitude angle and azimuth angle comprises the following steps:

And establishing a model of the water surface height and azimuth angle height angle screening range based on different water surface heights.

2. The method for complex GNSS-R water level altimetry of claim 1, wherein the GNSS-R solution comprises the steps of:

Carrying out water surface height calculation;

Delay-doppler analysis is performed.

3. A method for GNSS-R water level altimetry for complex situations as set forth in claim 2, wherein said water level calculation comprises the steps of:

performing GNSS dual-antenna water level monitoring;

and calculating satellite signal reflection point coordinates.

4. A method for GNSS-R water level altimetry for complex situations as set forth in claim 3, wherein said delay Doppler analysis comprises the steps of:

establishing a reflection point coordinate system;

and determining reflection point position information.

5. The method of claim 4, wherein the relational expression of the defined reflection point coordinate system and the delay Doppler domain is as follows:

6. The method of claim 5, wherein the mapping relation model between the coordinates of the coordinate system of the defined reflection point and the corresponding delay increment and Doppler shift is as follows:

7. The method of claim 1, wherein the eliminating condition is to eliminate satellite signals with altitude less than the altitude of the non-water surface reflection point within about 1 degree of the azimuth of the point by taking the azimuth and the altitude of the non-water surface reflection point as boundaries.