CN118817031A - A GNSS-R water surface height measurement method for complex situations - Google Patents

Abstract

The invention relates to a GNSS-R water surface height measurement method aiming at complex conditions, which comprises the following steps: 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. 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 the relation between the water level height and the screening of the height angle is established by repeatedly recording the height angle and the azimuth angle screening range of the same reservoir under different water levels, 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, different height angle screening ranges are selected according to the water level of time interval solution, and the solution precision of the water level is further improved.

Description

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

Technical Field

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

Background Art

The impact of the current global climate, floods and waterlogging disasters are caused by heavy rainfall, storm surges and other special reasons that lead to untimely drainage, resulting in waterlogging and flooding of land and houses. In order to minimize losses and protect people's lives and property safety, accurate and real-time water level monitoring is crucial in flood disasters, which can provide early warning and help decision makers take emergency measures.

There are two main types of traditional water level monitoring methods: contact methods and non-contact methods. However, in practical applications, traditional water level monitoring methods have some limitations and shortcomings: for example, contact methods require direct contact with the water surface, which is easily affected by pollutants or biological attachment, causing errors or damage; non-contact methods require the emission of electromagnetic waves or sound waves, which may interfere with or pollute the surrounding environment; in addition, traditional methods can usually only monitor water level changes at a single point or local area, and cannot achieve continuous monitoring over a large range or globally.

With the in-depth study of GNSS, the global satellite navigation system reflection measurement GNSS-R technology has been derived and applied to water level monitoring. Compared with traditional water level monitoring methods, GNSS-R water level monitoring technology has the advantages of low cost, low power consumption, all-weather, long-term continuity, stability, no calibration, high time resolution and wide coverage. In addition, since GNSS can provide accurate location information, GNSS-R technology can monitor the change of absolute height of the water surface. However, according to current research and analysis, for GNSS-R water surface monitoring, the water surface height result is easily affected by the reflection signal of non-water surface such as soil and vegetation, resulting in reduced accuracy of the solution result; and when the elevation angle azimuth screening method is used to remove the satellite signal in the direction of soil and vegetation, the elevation angle range screening often needs to be manually configured according to the on-site situation, which is costly and difficult; for reservoir applications, the water level may change greatly. When the water level is low, the reservoir wall will be exposed to the water surface, and this part will also reflect the satellite signal, affecting the positioning accuracy.

Summary of the invention

In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a GNSS-R water surface height measurement method for complex situations, so as to solve one or more problems in the prior art.

To achieve the above object, the technical solution of the present invention is as follows:

A GNSS-R water surface height measurement method for complex situations, characterized by comprising the following steps:

GNSS-R data reception;

Time matching;

GNSS-R solution;

Determination of the screening range of water surface height, satellite signal elevation angle and azimuth angle.

Furthermore, the GNSS data receiving comprises the following steps:

Receive GNSS signals through the upward-looking antenna and downward-looking antenna of the GNSS receiver;

GNSS signal data analysis;

Eliminate the GNSS satellite signals that do not meet the standards in the data set and complete the construction of the GNSS basic data set;

Solve for GNSS-R signal data.

Furthermore, the time matching includes the following steps:

storing received upward-looking antenna data or downward-looking antenna data;

Compare the time with the existing upward-looking antenna data or downward-looking antenna data. If the time is the same, enter the solution. If the time is different, eliminate the earlier data and store the uneliminated data waiting for new data input.

Furthermore, the GNSS-R solution includes the following steps:

Calculate the water surface height;

Delayed Doppler analysis was performed.

Furthermore, the water surface height calculation includes the following steps:

Conduct GNSS dual-antenna water level monitoring;

Calculate the delay path △ρ between the up-view signal and the down-view signal;

Calculate the height h between the location of the water antenna and the horizontal plane;

Calculate the coordinates of the satellite signal reflection point.

Further, the delayed Doppler analysis comprises the following steps:

Establish the reflection point coordinate system;

Define the relationship expression between the reflection point coordinate system and the delay Doppler domain;

A mapping relationship model between the coordinates of the reflection point coordinate system and the corresponding delay increment and Doppler frequency shift is defined;

Determine the reflection point location information.

Furthermore, the relationship between the reflection point coordinate system and the delay Doppler domain is expressed as follows:

Where: (x, y) is the coordinate of the reflection point coordinate system, (τ _xy , f _{d, xy} ) is the delay increment and Doppler frequency shift corresponding to the reflection point; γ is the GNSS satellite elevation angle; h is the height from the receiving antenna to the reflection surface, is the GNSS satellite speed.

Furthermore, the mapping relationship model between the coordinates of the reflection point coordinate system and the corresponding delay increment and Doppler frequency shift is shown in the following formula:

Where: (x, y) is the coordinate of the reflection point coordinate system, (τ _xy , f _{d, xy} ) is the delay increment and Doppler frequency shift corresponding to the reflection point; γ is the GNSS satellite elevation angle; h is the height from the receiving antenna to the reflection surface, is the GNSS satellite velocity, and (X _i ,Y _i ) is the mapping function.

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

Determine the non-water surface reflection point and the azimuth and altitude angle of the non-water surface reflection point;

Determine the azimuth and altitude angles of satellite signal screening. If the signal meets the elimination conditions, it will be eliminated. If not, the signal data will be recorded.

Establish water surface height and azimuth elevation angle screening ranges.

Furthermore, the elimination condition is to use the azimuth and altitude of the non-water surface reflection point as the boundary, and all satellite signals within 1° around the azimuth of this point and with an altitude angle less than the altitude angle of this point are eliminated.

Compared with the prior art, the beneficial technical effects of the present invention are as follows:

(I) The present invention uses the delayed Doppler method to analyze the properties around the reflection point, distinguish between water bodies and soil vegetation, determine the location of the soil vegetation by establishing a model, and then determine whether the coordinates of the reflection point are located in the soil vegetation area, and record its azimuth and altitude angles, and finally obtain the correct altitude and azimuth screening range, thereby improving the accuracy of the water surface height solution results.

(ii) The present invention establishes a relationship between water level and elevation angle screening by repeatedly recording the elevation angle and azimuth angle screening ranges at different water level 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. Different elevation angle screening ranges are selected according to the water level solved in the time period, thereby improving the accuracy of water surface height calculation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram showing an overall flow chart of a GNSS-R water surface height measurement method for complex situations according to an embodiment of the present invention.

FIG2 is a schematic diagram showing a detailed flow chart of a GNSS-R water surface height measurement method for complex situations according to an embodiment of the present invention.

FIG3 shows a schematic diagram of dual-antenna water level monitoring of a GNSS-R water surface height measurement method for complex situations according to an embodiment of the present invention.

DETAILED DESCRIPTION

In order to make the purpose, technical scheme and advantages of the present invention clearer, the following is a further detailed description of a GNSS-R water surface height measurement method for complex situations proposed by the present invention in combination with the accompanying drawings and specific embodiments. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the accompanying drawings are in a very simplified form and use non-precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, please refer to the accompanying drawings. It should be noted that the structure, proportion, size, etc. illustrated in the drawings of this specification are only used to match the content disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no technical substantive significance. Any structural modification, change in proportional relationship or adjustment of size, without affecting the effect that the present invention can produce and the purpose that can be achieved, should still fall within the scope of the technical content disclosed by the present invention.

Please refer to FIG. 1 and FIG. 2 , a GNSS-R water surface height measurement method for complex situations, characterized by comprising the following steps:

Step 1: GNSS-R data reception.

Step 1.1: Receive GNSS signals through the upward-looking antenna and downward-looking antenna of the GNSS receiver: The direct antenna of the GNSS receiver, i.e. the upward-looking antenna, is used as the base station, and the reflective antenna, i.e. the downward-looking antenna, is used as the rover.

Step 1.2: GNSS signal data analysis: Through analysis, the elevation angle (ele), carrier-to-noise ratio (C/N ⁰ ), azimuth angle (az) and pseudorange error of the satellite signal are obtained.

Furthermore, when the receiver position (x _t , y _t , z _t ) is known, the inverted pseudorange ρ ^t can be obtained, as shown in the following equation 1:

Where: is the clock error calculated by the receiver, is the correction value of the satellite clock error, I is the ionospheric delay obtained by the Klobuchar model, T is the tropospheric delay obtained by the Saastamoinen model, c is the speed of light, (x _t , y _t , z _t ) represents the receiver coordinates, and (x _s , y _s , z _s ) represents the satellite coordinates.

Furthermore, through the pseudorange ρ actually received and the simulated pseudorange ρ ^t obtained by inversion, the pseudorange error △ρ can be expressed as shown in the following formula 2:

Where: and They represent the residuals of the receiver clock error and the satellite clock error, △I and △T represent the parts that are not offset by the ionospheric delay obtained by the Klobuchar model and the tropospheric delay obtained by the Saastamoinen model, respectively, and ε is the noise.

Step 1.3: Eliminate GNSS satellite signals in the dataset whose satellite elevation angle and carrier-to-noise ratio do not meet the standards, and complete the construction of the GNSS basic dataset.

Step 1.4: Solve for GNSS-R signal data.

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

Furthermore, the direct Beidou navigation signal is as follows:

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

Furthermore, the Beidou navigation signal reflected by the water surface is shown in equation 4 below:

Where: τ is the delayed signal, τ=s/c, s is the extra distance the reflected signal travels, c is the speed of light, j is the satellite number, S is the satellite signal, t is time, and f is the signal frequency.

Furthermore, the additional distance s traveled by the reflected signal 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:

Step 2: Time matching. After the GNSS data is received, the data from the direct antenna and the reflective antenna will be time matched, and the direct signal and the reflected signal at the same time will enter the solution program.

Step 2.1: Storing the received upward-looking antenna data or downward-looking antenna data: Whenever data is received, first store the received direct-view antenna data or reflected-view antenna data.

Step 2.2: Compare the time with the existing reflection antenna data or direct antenna data, that is, compare the direct antenna data time with the reflection antenna data time. If the time is the same, enter the solution; if the time is different, remove the earlier data and store the other data to wait for new data input.

Step 3: GNSS-R solution.

Step 3.1: Calculate the water surface height.

Step 3.1.1 Perform GNSS dual-antenna water level monitoring: Please continue to refer to Figure 3. It can be seen from the figure that compared with the direct signal received by the sky antenna, the reflected signal received by the water antenna has an additional propagation path. Therefore, the water antenna can 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 surface height changes, the additional propagation path of the reflected signal will change, and the position of the virtual antenna will also change accordingly.

Step 3.1.2: Calculate the delay path △ρ between the upward and downward looking signals: When the receiving platform is at a relatively low ground altitude, it can be assumed that the earth is locally flat. This altitude depends on the observed incident angle and the user's tolerance for errors caused by this assumption. The error in the vertical component of the mirror point position when the earth is assumed to be flat is shown compared to the case where the earth is assumed to be spherical. Only incident angles up to 50° are included, and errors increase rapidly beyond these angles. Under this assumption, the delay path between the direct signal and the reflected signal can be expressed as shown in the following equation 6:

△ρ＝(2h+s)sinθ(6)

Step 3.1.3: Calculate the height h between the water antenna location and the horizontal plane: The height between the water antenna location and the horizontal plane can be expressed as shown in the following formula 7:

Where: △ρ is the delay path, h is the height from the phase center of the water antenna to the water surface, s is the distance between the phase midlines of the two antennas, and θ is the satellite elevation angle at the mirror reflection point.

Furthermore, by accurately knowing the position of the receiver, the height of the water surface relative to a reference surface, such as an ellipsoid, geoid or other terrain model, can be obtained.

Step 3.1.4: Calculate the coordinates of the satellite signal reflection point. With the known water surface height h, satellite azimuth angle ψ and altitude angle θ, and upward-looking antenna coordinates (x, y, z), the water surface reflection is considered to be specular reflection. The coordinates of the satellite signal reflection point (xi _{, yi} , _z ) can be obtained by geometric methods, as shown in the following equation 8:

(x _i , y _i , z _i )=(x, y, z)+(hcotθsinψ,hcotθcosψ,h)×R(8)

Where: R is the coordinate system transformation matrix.

Step 3.2: Perform delay Doppler analysis. The forward scattering of the reflected signal at the sea level mainly includes specular reflection or diffuse scattering. Due to the roughness of the reflecting surface, the characteristics of the reflected signal are relatively complex, which is manifested as the attenuation of the signal amplitude and the superposition of different time delays and different Doppler signals. The interval between the equal delay lines can be defined as the equal delay zone, and the signal delay in this interval is the same. Different time delays and Dopplers correspond to different reflection units of the reflecting surface, and the delay Doppler map can accurately quantify the reflection characteristics of each unit area from two aspects: time delay and frequency. Therefore, the reflection intensity of different reflection surface units is described by the delay Doppler image, and the maximum value of its amplitude can be used to describe the reflectivity of the reflecting medium to the GNSS reflected signal; the time delay of its two-dimensional correlation value can be used to describe the path delay relationship of the reflected signal relative to the direct signal, and the different reflecting surfaces of the reflecting objects directly determine the delay relationship.

Step 3.2.1: Establish the reflection point coordinate system: Take the plane perpendicular to the reflection normal and passing through the reflection point as the xoy plane, the projection of the signal incident ray on the plane as the y-axis, and the reflection normal as the z-axis to establish a spatial rectangular coordinate system, which can be called the reflection point coordinate system.

Step 3.2.2: Define the relationship between the reflection point coordinate system and the delay Doppler domain as shown in equations 9 and 10:

Where: (x, y) is the coordinate of the reflection point coordinate system, (τ _xy , f _{d, xy} ) is the delay increment and Doppler frequency shift corresponding to the reflection point, γ is the GNSS satellite elevation angle, h is the height from the receiving antenna to the reflection surface, which can be obtained by the angle of the dam, the antenna height, and the distance from the antenna to the bottom of the dam. is the GNSS satellite speed.

Step 3.2.3: Define the mapping relationship model between the coordinates of the reflection point coordinate system and the corresponding delay increment and Doppler frequency shift as shown in the following equation 11:

Where: (x, y) is the coordinate of the reflection point coordinate system, (τ _xy , f _{d, xy} ) is the delay increment and Doppler frequency shift corresponding to the reflection point, γ is the GNSS satellite elevation angle, h is the height from the receiving antenna to the reflection surface, is the GNSS satellite velocity, (X _i ,Y _i ) is the mapping function. .

Step 3.2.4: Determine the location information of the reflection point: After mapping, the soil and vegetation information around the reflection point will be projected onto the reflection surface, thereby determining whether it is a water surface.

Step 4: Determine the screening range of water surface height, satellite signal elevation angle and azimuth angle.

Step 4.1: Determine the non-water surface reflection point and the azimuth and altitude angle of the non-water surface reflection point: When calculating the coordinates of the reflection point through delayed Doppler, the information of the reflection surface around the reflection point will be obtained at the same time. On the one hand, a three-dimensional model will be established through the coordinates of the reflection point, and the azimuth of the satellite signal screening will be set according to the model situation; on the other hand, the material information of the reflection point and the surrounding reflection surface will be compared with the water surface to distinguish soil vegetation from the water surface, and assist in determining the edge of the water surface.

Step 4.2: Determine the azimuth and altitude angles of the satellite signal screening. If it meets the elimination conditions, it will be eliminated. If it does not meet the conditions, the signal data will be recorded.

Furthermore, the elimination condition uses the azimuth and altitude of the non-water surface reflection point as the boundary, and all satellite signals within 1 degree around the azimuth of this point and with an altitude angle less than the altitude angle of this point are eliminated.

Step 4.3: Establish the water surface height and azimuth elevation angle screening range: Calculate the water surface height again and record the relationship between the water surface height and the azimuth elevation angle screening range at this time. When the water surface height changes by more than 5 to 10 meters, determine the azimuth and elevation angle screening range again according to the changed water surface conditions, and record the corresponding relationship between the azimuth and elevation angle screening range and the water surface height in hours, and establish a model. Then the elevation angle screening range can be adjusted in time according to the implemented water surface height conditions and the model.

The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims (10)

1. 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.

2. The method for complex GNSS-R water surface altimetry according to claim 1, wherein: 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.

3. The method for complex GNSS-R water surface altimetry according to claim 1, wherein: the time matching comprises the following steps:

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.

4. The method for complex GNSS-R water surface altimetry according to claim 1, wherein: the GNSS-R solution comprises the following steps:

Carrying out water surface height calculation;

delay-doppler analysis is performed.

5. The method for complex GNSS-R water surface altimetry of claim 4, wherein: the water surface height calculation comprises the following steps:

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.

6. The method for complex GNSS-R water surface altimetry of claim 5, wherein: 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.

7. The method for complex GNSS-R water surface altimetry of claim 6, wherein: the relational expression defining the reflecting point coordinate system and the delay Doppler domain is shown as follows:

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

8. The method for complex GNSS-R water surface altimetry of claim 7, wherein: 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 follows:

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

9. The method for complex GNSS-R water surface altimetry according to claim 1, wherein: the determination 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.

10. The method for complex GNSS-R water surface altimetry of claim 9, wherein: the eliminating condition is that 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 are eliminated within the range of about 1 degree 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.