Method and system for calibrating mirror reflection points of land-based satellite-borne GNSS reflection signals

Abstract

The present invention provides a method and system for calibrating mirror reflection points of a land-based satellite-borne GNSS reflection signal, and relates to the technical field of mirror reflection point calibration, including obtaining an initial mirror reflection point set; the initial mirror reflection point set is determined by a global navigation satellite system that equates a land area to be measured to a spherical model or an ellipsoidal model; obtaining any initial mirror reflection point as a current initial mirror reflection point; determining a current approximate reflection surface according to the elevation data of the current initial mirror reflection point; determining a decision variable of the current initial mirror reflection point according to the current approximate reflection surface; and calibrating the current initial mirror reflection point according to the decision variable. The present invention constructs a current approximate reflection surface through the elevation data of the reflection point, and determines the mirror reflection point by equating the land area to be measured to a spherical model or an ellipsoidal model based on the correction of the current approximate reflection surface. The corrected mirror reflection point is suitable for land-based satellite-borne GNSS, and the measurement accuracy of land-based satellite-borne GNSS is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of mirror reflection point calibration, and in particular to a method and system for calibrating a mirror reflection point of a land-based satellite-borne GNSS reflection signal. Background Art

[0002] The geometric relationship of spaceborne GNSS-R (Global Navigation Satellite System Reflectometry) is the basis for GNSS-R to analyze the time, space and signal characteristics. It mainly describes the absolute and relative relationship between the GNSS-R space system and the GNSS satellite, mirror reflection point and low-orbit satellite in the space system. Spaceborne GNSS-R is a mirror detection technology. Whether it is to use a narrow beam antenna to point to the mirror reflection point to receive the reflected signal, or to choose to process the mirror reflection signal within the antenna coverage range, it is necessary to calculate the pointing angle, select the signal delay, and capture the signal within the Doppler range based on the estimation of the GNSS-R mirror reflection point. Therefore, the mirror reflection point is an important reference point for the geometric relationship of spaceborne GNSS-R.

[0003] In satellite-borne scenarios, the influence of the earth's curvature must be considered: the reflecting surface is a curved surface, and the initial design goals of existing satellite-borne GNSS-R missions are all for ocean exploration, and the ocean can be modeled as a random rough surface that conforms to a certain probability distribution. Therefore, the commonly used coordinate system (such as the WGS-84 coordinate system) equates the earth model with an ellipsoid model, which is well suited for ocean remote sensing. However, for the land surface, the topography is complex and does not conform to the random distribution characteristics. The deviation between the mirror reflection point calculated using the ellipsoid model and the actual mirror reflection point is large: the mirror reflection path calculated by the satellite-borne GNSS-R mission based on the ellipsoid model, the original mirror reflection point calculated based on the ellipsoid model, the actual real mirror reflection path and the actual mirror reflection point are as follows: Figure 1 As shown. Figure 1 It can be seen that there is a big discrepancy between the real mirror reflection point and the original mirror reflection point calculated based on the ellipsoid model.

[0004] Existing methods for searching for specular reflection points include: golden section method, dichotomy method, Gleason algorithm, Wu algorithm, Wagner algorithm, ellipsoid algorithm and Adagrad adaptive algorithm, etc. These algorithms can estimate the position of specular reflection points on a spherical surface or ellipsoid surface. However, the actual reflecting surface of the land is not a smooth spherical surface or ellipsoid surface. The terrain undulation of the land surface requires the use of an elevation model to simulate the real terrain in the calculation. However, the ground elevation data products have limited resolution and are discontinuous functions, which cannot estimate the position of the specular reflection point on the actual land surface. Summary of the invention

[0005] The purpose of the present invention is to provide a method and system for calibrating mirror reflection points of land-based satellite-borne GNSS reflection signals, which can correct the mirror reflection points determined based on a spherical model or an ellipsoidal model using elevation data, thereby improving the measurement accuracy of land-based satellite-borne GNSS.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] A method for calibrating a mirror reflection point of a land-based satellite-borne GNSS reflection signal, comprising:

[0008] Acquire an initial set of specular reflection points; the initial set of specular reflection points is determined by a global navigation satellite system by converting the land area to be measured into a spherical model or an ellipsoidal model;

[0009] Get any initial specular reflection point as the current initial specular reflection point;

[0010] Determine the current approximate reflection surface according to the elevation data of the current initial mirror reflection point;

[0011] Determine a decision variable of the current initial specular reflection point according to the current approximate reflection surface;

[0012] The current initial specular reflection point is calibrated according to the decision variable.

[0013] Optionally, determining the current approximate reflection surface according to the elevation data of the current initial mirror reflection point includes:

[0014] Taking the current initial mirror reflection point as the center and the preset distance as the side length, construct the current nine-square grid;

[0015] Determine the average elevation of the area corresponding to all edge grids in the current nine-grid; the edge grid is the grid in the nine-grid except the grid where the current initial mirror reflection point is located;

[0016] The plane where the average elevation is located is determined as the current approximate reflection surface.

[0017] Optionally, the determining the decision variable of the current initial specular reflection point according to the current approximate reflection surface includes:

[0018] Get the incident angle θ of the incident signal i ;

[0019] Get the output angle θ of the output signal r ;

[0020] Determine the first angle φ between the projection of the incident signal on the current approximate reflection surface and the due east direction i ;

[0021] Determine the second angle φ between the projection of the outgoing signal on the current approximate reflection surface and the due east direction r ;

[0022] According to the incident angle, the exit angle, the first angle and the second angle, according to the formula ψ=|θ i -θ r |+r|φ i -φ r |Determine the decision variable of the current initial mirror reflection point; where ψ is the decision variable; r is the penalty coefficient; 0<r<1.

[0023] Optionally, calibrating the current initial specular reflection point according to the decision variable includes:

[0024] Determine whether the decision variable is less than a decision threshold, and obtain a first decision result;

[0025] If the first judgment result is yes, determining that the current initial mirror reflection point is a land mirror reflection point;

[0026] If the first judgment result is no, the current initial mirror reflection point is calibrated according to all edge grids in the current nine-grid.

[0027] Optionally, calibrating the current initial specular reflection point according to all edge grids in the current nine-grid includes:

[0028] Determine the midpoints of all edge grids in the current nine-grid as pseudo-mirror reflection points;

[0029] According to the current approximate reflection surface, determining the decision variable of each pseudo-mirror reflection point as a pseudo-decision variable;

[0030] Determine whether the minimum pseudo-decision variable is less than the decision threshold, and obtain a second judgment result;

[0031] If the second judgment result is yes, determining that the pseudo mirror reflection point corresponding to the minimum pseudo decision variable is the land mirror reflection point;

[0032] If the second judgment result is no, it is determined that the current initial specular reflection point is a quasi-diffuse reflection point.

[0033] Optionally, after calibrating the current initial mirror reflection point according to the decision variable, the method further includes:

[0034] The current initial specular reflection point returns to step "determining the current approximate reflection surface according to the elevation data of the current initial specular reflection point" until the initial specular reflection point set is traversed to obtain the land surface specular reflection point set and the quasi-diffuse reflection point set.

[0035] A land-based satellite-borne GNSS reflection signal mirror reflection point calibration system, comprising:

[0036] An initial specular reflection point set acquisition module is used to acquire an initial specular reflection point set; the initial specular reflection point set is determined by the global navigation satellite system by converting the land area to be measured into a spherical model or an ellipsoidal model;

[0037] A current initial mirror reflection point acquisition module is used to acquire any initial mirror reflection point as the current initial mirror reflection point;

[0038] A current approximate reflection surface determination module is used to determine the current approximate reflection surface according to the elevation data of the current initial mirror reflection point;

[0039] A decision variable determination module, used to determine the decision variable of the current initial specular reflection point according to the current approximate reflection surface;

[0040] A calibration module is used to calibrate the current initial mirror reflection point according to the decision variable.

[0041] Optionally, the current approximate reflecting surface determining module includes:

[0042] A current nine-square grid construction unit, used to construct a current nine-square grid with the current initial mirror reflection point as the center and a preset distance as the side length;

[0043] An average elevation determination unit is used to determine the average elevation of the areas corresponding to all edge grids in the current nine-grid; the edge grids are grids in the nine-grid except the grid where the current initial mirror reflection point is located;

[0044] The current approximate reflecting surface determining unit is used to determine the plane where the average elevation is located as the current approximate reflecting surface.

[0045] Optionally, the decision variable determination module includes:

[0046] An incident angle acquisition unit, used to acquire the incident angle θ of the incident signal i ;

[0047] An exit angle acquisition unit, used to acquire the exit angle θ of the exit signal r ;

[0048] The first angle determination unit is used to determine the first angle φ between the projection of the incident signal on the current approximate reflection surface and the due east direction. i ;

[0049] The second angle determination unit is used to determine the second angle φ between the projection of the outgoing signal on the current approximate reflection surface and the due east direction. r ;

[0050] A decision variable determination unit is used to determine the incident angle, the exit angle, the first angle and the second angle according to the formula ψ=|θ i -θ r |+r|φ i -φ r |Determine the decision variable of the current initial mirror reflection point; where ψ is the decision variable; r is the penalty coefficient; 0<r<1.

[0051] Optionally, the calibration module includes:

[0052] a first judgment unit, configured to judge whether the judgment variable is less than a judgment threshold value, and obtain a first judgment result; if the first judgment result is yes, calling a land surface mirror reflection point determination unit; if the first judgment result is no, calling a calibration unit;

[0053] A land surface specular reflection point determination unit, used to determine the current initial specular reflection point as the land surface specular reflection point;

[0054] The calibration unit is used to calibrate the current initial mirror reflection point according to all edge grids in the current nine-grid.

[0055] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0056] The present invention provides a method and system for calibrating mirror reflection points of a land-based satellite-borne GNSS reflection signal, including obtaining an initial mirror reflection point set; the initial mirror reflection point set is determined by the global navigation satellite system by equivalently treating the land area to be measured as a spherical model or an ellipsoidal model; obtaining any initial mirror reflection point as the current initial mirror reflection point; determining the current approximate reflection surface according to the elevation data of the current initial mirror reflection point; determining the decision variable of the current initial mirror reflection point according to the current approximate reflection surface; and calibrating the current initial mirror reflection point according to the decision variable. The present invention constructs the current approximate reflection surface through the elevation data of the reflection point, and determines the mirror reflection point by equivalently treating the land area to be measured as a spherical model or an ellipsoidal model based on the correction of the current approximate reflection surface. The corrected mirror reflection point is suitable for land-based satellite-borne GNSS, thereby improving the measurement accuracy of land-based satellite-borne GNSS. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0058] Figure 1The relationship between the real mirror reflection point and the original mirror reflection point according to the ellipsoid model in the prior art of the present invention is

[0059] Figure 2 This is a flow chart of the method for calibrating the mirror reflection point of the land-based satellite-borne GNSS reflection signal in Example 1 of the present invention;

[0060] Figure 3 It is a correlation diagram of the information to be inverted and the observed quantity in the surface area in Example 2 of the present invention;

[0061] Figure 4 This is a first calibration principle diagram in Embodiment 3 of the present invention;

[0062] Figure 5 This is a second calibration principle diagram in Example 3 of the present invention. DETAILED DESCRIPTION

[0063] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0064] The purpose of the present invention is to provide a method and system for calibrating mirror reflection points of land-based satellite-borne GNSS reflection signals, which can correct the mirror reflection points determined based on a spherical model or an ellipsoidal model using elevation data, thereby improving the measurement accuracy of land-based satellite-borne GNSS.

[0065] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0066] Example 1

[0067] like Figure 2 This embodiment provides a method for calibrating a mirror reflection point of a land-based satellite-borne GNSS reflection signal, including:

[0068] Step 101: obtaining an initial set of specular reflection points; the initial set of specular reflection points is determined by the global navigation satellite system by converting the land area to be measured into a spherical model or an ellipsoidal model;

[0069] Step 102: obtaining any initial specular reflection point as the current initial specular reflection point;

[0070] Step 103: determining the current approximate reflection surface according to the elevation data of the current initial mirror reflection point;

[0071] Step 103 includes: constructing the current nine-square grid with the current initial mirror reflection point as the center and the preset distance as the side length; determining the average elevation of the corresponding areas of all edge grids in the current nine-square grid; the edge grid is the grid in the nine-square grid except the grid where the current initial mirror reflection point is located; determining the plane where the average elevation is located is the current approximate reflection surface.

[0072] Step 104: determining a decision variable of a current initial mirror reflection point according to the current approximate reflection surface;

[0073] Step 104 includes: obtaining the incident angle θ of the incident signal i ; Get the emission angle θ of the emission signal r ; Determine the first angle φ between the projection of the incident signal on the current approximate reflection surface and the due east direction i ; Determine the second angle φ between the projection of the outgoing signal on the current approximate reflection surface and the due east direction r ; According to the incident angle, the exit angle, the first angle and the second angle, according to the formula ψ=|θ i -θ r |+r|φ i -φ r |Determine the decision variable of the current initial mirror reflection point; where ψ is the decision variable; r is the penalty coefficient; 0<r<1.

[0074] Step 105: Calibrate the current initial mirror reflection point according to the decision variable.

[0075] Step 105 includes: judging whether the judgment variable is less than the judgment threshold value, and obtaining a first judgment result. If the first judgment result is yes, determining that the current initial mirror reflection point is a land mirror reflection point.

[0076] If the first judgment result is no, the current initial mirror reflection point is calibrated according to all edge grids in the current nine-grid.

[0077] Calibrating the current initial mirror reflection point according to all edge grids in the current nine-square grid includes: determining the midpoint of all edge grids in the current nine-square grid as a pseudo-mirror reflection point; determining the decision variable of each pseudo-mirror reflection point as a pseudo-decision variable according to the current approximate reflection surface; judging whether the minimum pseudo-decision variable is less than the decision threshold, and obtaining a second judgment result; if the second judgment result is yes, determining the pseudo-mirror reflection point corresponding to the minimum pseudo-decision variable as a land mirror reflection point; if the second judgment result is no, determining the current initial mirror reflection point as a quasi-diffuse reflection point.

[0078] After step 105, the method further includes: obtaining the current initial specular reflection point and returning to step 103 until the initial specular reflection point set is traversed to obtain a land surface specular reflection point set and a quasi-diffuse reflection point set.

[0079] Example 2

[0080] This embodiment provides a calibration method with high algorithm efficiency and small result deviation. It creates an iterative algorithm for mirror point search based on the angle and the shortest path, using the GNSS-R geometric relationship and the nonlinear programming method, thereby realizing the estimation of the position of the real mirror reflection point.

[0081] Step 1: Obtain the most important observation quantity of the spaceborne GNSS-R: the delay-Doppler two-dimensional variable of the bistatic scattering correlation power, that is, the Delay Doppler Map (DDM), as shown in the formula:

[0082]

[0083] Here, <|Y(τ,f)| 2 > represents the correlation power between the reflected signal component with a time delay of τ and a Doppler frequency of f in the GNSS multipath reflected signal and the local pseudo-random code of the receiver, T i is the coherent integration time of the receiver; λ is the carrier wavelength of the GNSS signal; P t is the GNSS satellite transmission power; G t is the GNSS satellite transmitting antenna gain; G r (ρ) is the GNSS reflected signal receiving antenna gain; R0(ρ) is the range from the transmitter to the ground; R1(ρ) is the range from the ground to the receiver; is the bistatic radar scattering coefficient when the direct signal is p-polarized and the reflected signal is received using q-polarized; A represents the signal illumination area.

[0084] Step 2: DDM contains the information to be inverted on the reflecting surface. Combined with the equal delay area and equal Doppler area in the section, the relationship between the surface area information to be inverted and the DDM characteristic parameters (observables) is established. The mapping relationship is as follows Figure 3 .

[0085] Step 3: Assume the delay of the maximum power point of the onboard GNSS-R DDM is τ max , the Doppler shift is D max . Then the time delay of the reflection point S is defined as:

[0086] τ s =τ dir -δP (2)

[0087] where τ s is the code delay of the GNSS signal arriving at point s, τ dir is the code delay of the direct signal, and δP is the code delay of the direct reflected signal:

[0088]

[0089] In the formula, is the GNSS satellite vector transmitting signals from the center of the Earth, GNSS-R satellite vector of received signal, is the vector of the initial mirror reflection point S, and the physical meaning of δP is the difference between the reflected signal path and the direct path. It can represent:

[0090]

[0091] In the formula, It is a vector corresponding to a point on the earth ellipsoid model (such as WGS84) with latitude (lat′) and longitude offset (lon′), and ΔH is the elevation given by the DEM model.

[0092] Therefore, the time delay from the initial mirror reflection point S to the power maximum point can be defined as:

[0093] δτ=τ max -τ s (5)

[0094] Step 4: Define the Doppler shift D of the initial mirror reflection point S s :

[0095] D s =D R +D T +D clk (6)

[0096] Where D T is the Doppler frequency shift caused by the motion of the GNSS satellite, D R is the frequency shift caused by the motion of the GNSS-R satellite, D clk is the Doppler frequency shift caused by satellite mid-range offset. T and D R It can be calculated by formula (7) and (8) respectively:

[0097]

[0098]

[0099] In the formula, is the speed of the GNSS-R receiver, is the speed of the GNSS satellite, f is the carrier frequency of the GNSS signal, and c is the speed of light. The unit vector of the GNSS-R satellite motion on the current approximate reflecting surface RST, is the unit vector of the GNSS satellite moving on the current approximate reflection surface RST, where:

[0100]

[0101]

[0102] Therefore, the Doppler difference of the reflection point S relative to the DDM power maximum point can be expressed as:

[0103] δD=D max -D S (11)

[0104] Step 5: Considering the influence of terrain, the ground is divided into grids. S1, S2, S3, and S4 are the adjacent points (pseudo-mirror reflection points) of the reflection point S in the north, south, and east and west directions, respectively. Figure 4-5 shown.

[0105] Figure 4-5 In the equation, P1 is the incident vector of the GNSS signal; P2 is the outgoing vector of the GNSS signal, and P′1 and P′2 are their projections on the real surface. Since the position of the initial mirror reflection point S is calculated based on the ellipse model, it does not satisfy Snell's law (i.e., it does not satisfy θ i ≠θ r ).

[0106] For the convenience of analysis, a reference coordinate system ENU is defined with the initial mirror reflection point S as the center. The unit vector pointing due east; The unit vector pointing to the north direction; Unit vector pointing in the direction of the zenith:

[0107]

[0108]

[0109]

[0110] Project the incident vector P1 and the outgoing vector P2 onto the reflection plane in the ENU coordinate system:

[0111]

[0112] P′ 1,E , P′ 1,N and P′ 1,U They respectively represent the incident vector after the incident vector P1 is projected onto the E coordinate axis, the N coordinate axis and the coordinate system axis.

[0113]

[0114] P′ 2,E , P′ 2,N and P′ 2,UThey respectively represent the incident vector P2 after being projected onto the E coordinate axis, the N coordinate axis and the coordinate system axis.

[0115] Then we can obtain θ i ,θ r ,φ i and φ r :

[0116]

[0117]

[0118]

[0119]

[0120] Step 6: Based on θ i ,θ r ,φ i and φ r An iterative algorithm is established to correct the land surface mirror reflection points, as described below:

[0121] The first step of the algorithm:

[0122] 1.1) If Figure 4-5 , take the first initial pseudo-mirror reflection point S in the data set, use DEM to calculate the average elevation of eight adjacent units, and take the approximate reflection surface. Based on the approximate reflection surface, calculate the normal, various angles (including θ i ,θ r ,φ i and φ r ).

[0123] 1.2) Define the decision variable ψ = |θ i -θ r |+r|φ i -φ r |, 0<r<1 is the penalty coefficient. Let T0 be the decision threshold, if ψ s >T0, calculate the ψ values ​​of the center points of the eight neighborhood units of point S.

[0124] Otherwise, the loop is terminated, and point S is determined to be the best approximation of the mirror reflection point, and the point is included in the mirror reflection set.

[0125] 1.3) Take the minimum decision variable ψ′ of the eight neighborhoods. If ψ′<ψ s , and use this point as the new point S. Otherwise, terminate the loop and collect the point data into the non-mirror reflection set.

[0126] 1.4) Take the next pseudo-specular reflection point S in the data set and return to step 1.1). If all pseudo-specular reflection points S in the data set have been calculated, the algorithm ends and the specular reflection set and the quasi-diffuse reflection set are obtained. When inverting soil moisture or vegetation parameters later, different algorithms can be used for the two types of sets and different accuracy levels can be determined.

[0127] The second step of the algorithm:

[0128] 2.1) Preprocess the DDM of the reflection events in the diffuse reflection set to eliminate the influence of noise or overcorrection, and calculate the total energy of the diffuse reflection set Among them, M i,j Represents the value of the element in the i-th row and j-th column of ddm.

[0129] 2.2) Set the energy threshold E0 = ratio_k × E, (0 < ratio_k < 1), and set the element value M in DDM i,j Sort and calculate the first m elements whose energy sum is greater than the threshold, denoted as [M0,M1,...,M m ],Right now Where M0 is the maximum value of the DDM element, and m is the minimum value that satisfies the condition. The parameter ratio_k is a fraction greater than 0 and less than 1.

[0130] 2.3) Statistics [M0,M1,...,M m ]The probability of the position distribution of M0 is that the maximum probability interval where the M0 position is located is the main area of ​​reflected energy.

[0131] Finally, the corrected reflection points of the specular reflection set and the main reflection energy area of ​​the quasi-diffuse reflection set are obtained. The main reflection energy area is used to determine the main area of ​​detection and then establish an inversion model.

[0132] Example 3

[0133] This embodiment provides a terrestrial satellite-borne GNSS reflection signal mirror reflection point calibration system, including:

[0134] The initial specular reflection point set acquisition module is used to acquire the initial specular reflection point set; the initial specular reflection point set is determined by the global navigation satellite system by converting the land area to be measured into a spherical model or an ellipsoidal model.

[0135] The current initial specular reflection point acquisition module is used to acquire any initial specular reflection point as the current initial specular reflection point.

[0136] The current approximate reflection surface determination module is used to determine the current approximate reflection surface according to the elevation data of the current initial mirror reflection point.

[0137] The decision variable determination module is used to determine the decision variable of the current initial mirror reflection point according to the current approximate reflection surface.

[0138] The calibration module is used to calibrate the current initial mirror reflection point according to the decision variable.

[0139] Among them, the current approximate reflection surface determination module includes: a current nine-square grid construction unit, which is used to construct the current nine-square grid with the current initial mirror reflection point as the center and a preset distance as the side length; an average elevation determination unit, which is used to determine the average elevation of the corresponding areas of all edge grids in the current nine-square grid; the edge grid is the grid in the nine-square grid except the grid where the current initial mirror reflection point is located; the current approximate reflection surface determination unit is used to determine that the plane where the average elevation is located is the current approximate reflection surface.

[0140] Specifically, the decision variable determination module includes: an incident angle acquisition unit, used to obtain the incident angle θ of the incident signal i ; An exit angle acquisition unit, used to obtain the exit angle θ of the exit signal r ; A first angle determination unit, used to determine a first angle φ between the projection of the incident signal on the current approximate reflection surface and the due east direction i ; A second angle determination unit, used to determine a second angle φ between the projection of the outgoing signal on the current approximate reflection surface and the due east direction r ; A decision variable determination unit is used to determine the incident angle, the exit angle, the first angle and the second angle according to the formula ψ=|θ i -θ r |+r|φ i -φ r |Determine the decision variable of the current initial mirror reflection point; where ψ is the decision variable; r is the penalty coefficient; 0<r<1.

[0141] In addition, the calibration module includes: a first judgment unit, used to judge whether the judgment variable is less than the judgment threshold to obtain a first judgment result; if the first judgment result is yes, calling the land surface mirror reflection point determination unit; if the first judgment result is no, calling the calibration unit; the land surface mirror reflection point determination unit, used to determine that the current initial mirror reflection point is the land surface mirror reflection point; the calibration unit, used to calibrate the current initial mirror reflection point according to all edge grids in the current nine-square grid.

[0142] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0143] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for calibrating the mirror reflection point of a land-based satellite-borne GNSS reflection signal, characterized in that: include: Acquire an initial set of specular reflection points; the initial set of specular reflection points is determined by a global navigation satellite system by converting the land area to be measured into a spherical model or an ellipsoidal model; Get any initial specular reflection point as the current initial specular reflection point; Determine the current approximate reflection surface according to the elevation data of the current initial mirror reflection point; Determine a decision variable of the current initial specular reflection point according to the current approximate reflection surface; Calibrate the current initial mirror reflection point according to the decision variable; The step of determining the decision variable of the current initial specular reflection point according to the current approximate reflection surface comprises: Get the incident angle θ of the incident signal i ; Get the output angle θ of the output signal r ; Determine the first angle φ between the projection of the incident signal on the current approximate reflection surface and the due east direction i ; Determine the second angle φ between the projection of the outgoing signal on the current approximate reflection surface and the due east direction r ; According to the incident angle, the exit angle, the first angle and the second angle, according to the formula ψ=|θ i -θ r |+rφ i -φ r |Determine the decision variable of the current initial mirror reflection point; where ψ is the decision variable; r is the penalty coefficient; 0<r<1.

2. The method for calibrating the mirror reflection point of the land-based satellite-borne GNSS reflection signal according to claim 1, characterized in that: The step of determining the current approximate reflection surface according to the elevation data of the current initial mirror reflection point comprises: Taking the current initial mirror reflection point as the center and the preset distance as the side length, construct the current nine-square grid; Determine the average elevation of the area corresponding to all edge grids in the current nine-grid; the edge grid is the grid in the nine-grid except the grid where the current initial mirror reflection point is located; The plane where the average elevation is located is determined as the current approximate reflection surface.

3. The method for calibrating the mirror reflection point of the land-based satellite-borne GNSS reflection signal according to claim 2 is characterized in that: The step of calibrating the current initial mirror reflection point according to the decision variable comprises: Determine whether the decision variable is less than a decision threshold, and obtain a first decision result; If the first judgment result is yes, determining that the current initial mirror reflection point is a land mirror reflection point; If the first judgment result is no, the current initial mirror reflection point is calibrated according to all edge grids in the current nine-grid.

4. The method for calibrating the mirror reflection point of the land-based satellite-borne GNSS reflection signal according to claim 3 is characterized in that: The step of calibrating the current initial mirror reflection point according to all edge grids in the current nine-grid comprises: Determine the midpoints of all edge grids in the current nine-grid as pseudo-mirror reflection points; According to the current approximate reflection surface, determining the decision variable of each pseudo-mirror reflection point as a pseudo-decision variable; Determine whether the minimum pseudo-decision variable is less than the decision threshold, and obtain a second judgment result; If the second judgment result is yes, determining that the pseudo mirror reflection point corresponding to the minimum pseudo decision variable is the land mirror reflection point; If the second judgment result is no, it is determined that the current initial specular reflection point is a quasi-diffuse reflection point.

5. The method for calibrating the mirror reflection point of the land-based satellite-borne GNSS reflection signal according to claim 4, characterized in that: After calibrating the current initial mirror reflection point according to the decision variable, the method further includes: The current initial specular reflection point and return to step "determining the current approximate reflection surface according to the elevation data of the current initial specular reflection point" until the initial specular reflection point set is traversed to obtain the land surface specular reflection point set and the quasi-diffuse reflection point set.

6. A land-based satellite-borne GNSS reflection signal mirror reflection point calibration system, characterized in that: include: An initial specular reflection point set acquisition module is used to acquire an initial specular reflection point set; the initial specular reflection point set is determined by the global navigation satellite system by converting the land area to be measured into a spherical model or an ellipsoidal model; A current initial mirror reflection point acquisition module is used to acquire any initial mirror reflection point as the current initial mirror reflection point; A current approximate reflection surface determination module is used to determine the current approximate reflection surface according to the elevation data of the current initial mirror reflection point; A decision variable determination module, used to determine the decision variable of the current initial specular reflection point according to the current approximate reflection surface; A calibration module, used for calibrating the current initial mirror reflection point according to the decision variable; The decision variable determination module comprises: An incident angle acquisition unit, used to acquire the incident angle θ of the incident signal i ; An exit angle acquisition unit, used to acquire the exit angle θ of the exit signal r ; The first angle determination unit is used to determine the first angle φ between the projection of the incident signal on the current approximate reflection surface and the due east direction. i ; The second angle determination unit is used to determine the second angle φ between the projection of the outgoing signal on the current approximate reflection surface and the due east direction. r ; A decision variable determination unit is used to determine the incident angle, the exit angle, the first angle and the second angle according to the formula ψ=|θ i -θ r |+rφ i -φ r |Determine the decision variable of the current initial mirror reflection point; where ψ is the decision variable; r is the penalty coefficient; 0<r<1.

7. The terrestrial satellite-borne GNSS reflection signal mirror reflection point calibration system according to claim 6, characterized in that: The current approximate reflecting surface determination module comprises: A current nine-square grid construction unit, used to construct a current nine-square grid with the current initial mirror reflection point as the center and a preset distance as the side length; An average elevation determination unit is used to determine the average elevation of the areas corresponding to all edge grids in the current nine-grid; the edge grids are grids in the nine-grid except the grid where the current initial mirror reflection point is located; The current approximate reflecting surface determining unit is used to determine the plane where the average elevation is located as the current approximate reflecting surface.

8. The land-based satellite-borne GNSS reflection signal mirror reflection point calibration system according to claim 7, characterized in that: The calibration module comprises: a first judgment unit, configured to judge whether the judgment variable is less than a judgment threshold value, and obtain a first judgment result; if the first judgment result is yes, calling a land surface mirror reflection point determination unit; if the first judgment result is no, calling a calibration unit; A land surface specular reflection point determination unit, used to determine the current initial specular reflection point as the land surface specular reflection point; The calibration unit is used to calibrate the current initial mirror reflection point according to all edge grids in the current nine-grid.

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