CN115047503A - Method and system for calibrating mirror reflection point of land-based satellite-borne GNSS (Global navigation satellite System) reflection signal - Google Patents
Method and system for calibrating mirror reflection point of land-based satellite-borne GNSS (Global navigation satellite System) reflection signal Download PDFInfo
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Abstract
The invention provides a calibration method and a system for a terrestrial satellite-borne GNSS reflected signal specular reflection point, which relate to the technical field of specular reflection point calibration and comprise the steps of obtaining an initial specular reflection point set; the initial mirror reflection point set is determined by the global navigation satellite system to enable the land area to be measured to be equivalent to a spherical model or an ellipsoidal model; acquiring any initial specular reflection point as a current initial specular reflection point; determining a current approximate reflecting surface according to elevation data of a current initial specular reflection point; determining a decision variable of a current initial specular reflection point according to the current approximate reflection surface; and calibrating the current initial specular reflection point according to the decision variable. According to the method, the current approximate reflecting surface is constructed through the elevation data of the reflecting points, the land area to be measured is equivalent to a spherical surface model or an ellipsoidal surface model based on the correction of the current approximate reflecting surface, the mirror reflecting points are determined, the corrected mirror reflecting points are suitable for the land satellite-borne GNSS, and the measurement accuracy of the land satellite-borne GNSS is improved.
Description
Technical Field
The invention relates to the technical field of mirror reflection point calibration, in particular to a method and a system for calibrating a mirror reflection point of a land satellite-borne GNSS reflection signal.
Background
The geometric relation of the satellite-borne GNSS-R (global navigation satellite system reflection measurement) is the basis of the GNSS-R for analyzing space-time and signal characteristics, and mainly describes the absolute relation and the relative relation between the space system of the GNSS-R and the GNSS satellite, the specular reflection point and the low-orbit satellite in the space system. The satellite-borne GNSS-R is a mirror direction detection technology, and whether a narrow beam antenna is used for pointing to a mirror reflection point to receive a reflection signal or the mirror reflection signal is selected to be processed in an antenna coverage range, the pointing angle calculation, the signal delay selection and the signal capture processing in a Doppler range are carried out on the basis of the estimation of the GNSS-R mirror reflection point, so that the mirror reflection point is an important reference point of the satellite-borne GNSS-R geometric relation.
The influence of the earth curvature must be considered in a space-borne scenario: the reflecting surface is a curved surface, the designed initial targets of the existing satellite-borne GNSS-R task are ocean exploration, the ocean can be modeled into a random rough surface which accords with certain probability distribution, and therefore the earth model is equivalent to an ellipsoid model by a common coordinate system (such as a WGS-84 coordinate system) and the method can be well suitable for ocean remote sensing. However, for the land surface, the landform is complex and does not conform to the random distribution characteristic, and the deviation between the specular reflection point calculated by using the ellipsoid model and the actual specular reflection point is large: the current satellite-borne GNSS-R task is shown in figure 1 according to a mirror reflection path obtained by calculation of an ellipsoid model, an original mirror reflection point obtained by calculation of the ellipsoid model, an actual real mirror reflection path and an actual mirror reflection point. As can be seen from fig. 1: the real specular reflection point and the original specular reflection point calculated according to the ellipsoid model have larger access.
The existing mirror reflection point searching method comprises the following steps: the method comprises a golden section method, a dichotomy method, a Gleason algorithm, a Wu algorithm, a Wagner algorithm, an ellipsoid algorithm, an Adagrad adaptive algorithm and the like, wherein the algorithms can realize the position estimation of the mirror reflection point on the spherical surface or the ellipsoid. However, the actual reflecting surface of the land is not a smooth spherical surface or an ellipsoid, the topography of the land needs to be simulated by using an elevation model in calculation, and ground elevation data products have limited resolution and are discontinuous functions, so that the position estimation of the specular reflection point on the actual reflecting surface of the land cannot be realized.
Disclosure of Invention
The invention aims to provide a calibration method and a calibration system for a reflection point of a terrestrial satellite-borne GNSS (global navigation satellite system) reflection signal, which can be used for correcting the reflection point of a mirror surface determined based on a spherical model or an ellipsoidal model by utilizing elevation data and improving the measurement accuracy of the terrestrial satellite-borne GNSS.
In order to achieve the purpose, the invention provides the following scheme:
a calibration method for a specular reflection point of a terrestrial satellite-borne GNSS reflection signal comprises the following steps:
acquiring an initial specular reflection point set; the initial specular reflection point set is determined by a global navigation satellite system to enable a land area to be measured to be equivalent to a spherical surface model or an ellipsoidal surface model;
acquiring any initial specular reflection point as a current initial specular reflection point;
determining a current approximate reflecting surface according to elevation data of a current initial specular reflection point;
determining a decision variable of the current initial specular reflection point according to the current approximate reflecting surface;
and calibrating the current initial specular reflection point according to the decision variable.
Optionally, the determining a current approximate reflecting surface according to the elevation data of the current initial specular reflection point includes:
constructing a current nine-square grid by taking the current initial specular reflection point as a center and a preset distance as a side length;
determining the average elevation of areas corresponding to all edge grids in the current nine-square grid; the edge grids are grids except the grid where the current initial specular reflection point is located in the nine-square grid;
and determining the plane where the average elevation is located as the current approximate reflecting surface.
Optionally, the determining a decision variable of the current initial specular reflection point according to the current approximate reflecting surface includes:
obtaining an incident angle theta of an incident signal i ；
Obtaining the emergent angle theta of the emergent signal r ；
Determining a first included angle phi between the projection of the incident signal on the current approximate reflecting surface and the east direction i ；
Determining a second included angle phi between the projection of the emergent signal on the current approximate reflecting surface and the east direction r ；
According to the incident angle, the exit angle, the first included angle and the second included angle, according to a formula psi ═ theta i -θ r |+r|φ i -φ r Determining a judgment variable of a current initial specular reflection point; wherein psi is a decision variable; r is a penalty coefficient; r is more than 0 and less than 1.
Optionally, the calibrating the current initial specular reflection point according to the decision variable includes:
judging whether the judgment variable is smaller than a judgment threshold value or not to obtain a first judgment result;
if the first judgment result is yes, determining that the current initial mirror surface reflection point is a land mirror surface reflection point;
and if the first judgment result is negative, calibrating the current initial specular reflection point according to all the edge grids in the current nine-square grid.
Optionally, the calibrating the current initial specular reflection point according to all edge lattices in the current nine-square lattice includes:
determining the middle points of all edge lattices in the current nine-square lattice as pseudo mirror reflection points;
determining a decision variable of each pseudo mirror reflection point as a pseudo decision variable according to the current approximate reflection surface;
judging whether the minimum false judgment variable is smaller than a judgment threshold value or not to obtain a second judgment result;
if the second judgment result is yes, determining a pseudo mirror surface reflection point corresponding to the minimum pseudo judgment variable as a land mirror surface reflection point;
and if the second judgment result is negative, determining that the current initial specular reflection point is a diffuse reflection-like point.
Optionally, after the calibrating the current initial specular reflection point according to the decision variable, the method further includes:
and (3) current initial specular reflection points and returning to the step of determining a current approximate reflecting surface according to the elevation data of the current initial specular reflection points until the initial specular reflection point set is passed, so as to obtain a terrestrial mirror surface reflection point set and a diffuse reflection point-like set.
A system for calibrating specular reflection points of terrestrial satellite-borne GNSS reflected signals comprises:
the initial specular reflection point set acquisition module is used for acquiring an initial specular reflection point set; the initial specular reflection point set is determined by the global navigation satellite system to enable the land area to be measured to be equivalent to a spherical model or an ellipsoidal model;
the current initial specular reflection point acquisition module is used for acquiring any initial specular reflection point as a current initial specular reflection point;
the current approximate reflecting surface determining module is used for determining a current approximate reflecting surface according to the elevation data of the current initial specular reflection point;
a decision variable determining module, configured to determine a decision variable of the current initial specular reflection point according to the current approximate reflecting surface;
and the calibration module is used for calibrating the current initial specular reflection point according to the judgment variable.
Optionally, the current approximate reflecting surface determining module includes:
the current nine-grid construction unit is used for constructing a current nine-grid by taking the current initial specular reflection point as a center and a preset distance as a side length;
the average elevation determining unit is used for determining the average elevation of areas corresponding to all the edge grids in the current nine-square grid; the edge grids are grids except the grid where the current initial specular reflection point is located in the nine-square grid;
and the current approximate reflecting surface determining unit is used for determining the plane where the average elevation is located as the current approximate reflecting surface.
Optionally, the decision variable determining module includes:
an incident angle acquiring unit for acquiring an incident angle theta of the incident signal i ；
An exit angle acquisition unit for acquiring an exit angle theta of the exit signal r ；
A first included angle determining unit for determining a first included angle phi between the projection of the incident signal on the current approximate reflecting surface and the east direction i ；
A second included angle determining unit for determining a second included angle phi between the projection of the emergent signal on the current approximate reflecting surface and the east direction r ；
A decision variable determining unit for determining a first angle from the incident angle, the exit angle, the first angle and the second angle according to a formula psi ═ theta i -θ r |+r|φ i -φ r Determining a judgment variable of a current initial specular reflection point; wherein psi is a decision variable; r is a penalty coefficient; r is more than 0 and less than 1.
Optionally, the calibration module includes:
the first judgment unit is used for judging whether the judgment variable is smaller than a judgment threshold value or not to obtain a first judgment result; if the first judgment result is yes, calling a terrestrial mirror surface reflection point determining unit; if the first judgment result is negative, calling a calibration unit;
the land mirror surface reflection point determining unit is used for determining the current initial mirror surface reflection point as a land mirror surface reflection point;
and the calibration unit is used for calibrating the current initial specular reflection point according to all the edge grids in the current nine-square grid.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention provides a calibration method and a system for a terrestrial satellite-borne GNSS reflected signal specular reflection point, which comprises the steps of obtaining an initial specular reflection point set; the initial specular reflection point set is determined by the global navigation satellite system to enable the land area to be measured to be equivalent to a spherical surface model or an ellipsoidal surface model; acquiring any initial specular reflection point as a current initial specular reflection point; determining a current approximate reflecting surface according to elevation data of a current initial specular reflection point; determining a decision variable of a current initial mirror reflection point according to the current approximate reflection surface; and calibrating the current initial specular reflection point according to the decision variable. According to the method, the current approximate reflecting surface is constructed through the elevation data of the reflecting points, the land area to be measured is equivalent to a spherical surface model or an ellipsoidal surface model based on the correction of the current approximate reflecting surface, the mirror reflecting points are determined, the corrected mirror reflecting points are suitable for the land satellite-borne GNSS, and the measurement accuracy of the land satellite-borne GNSS is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a graph showing the relationship between real specular reflection points and original specular reflection points according to an ellipsoid model in the prior art
FIG. 2 is a flowchart illustrating a method for calibrating specular reflection points of terrestrial satellite-borne GNSS reflected signals according to an embodiment 1 of the present invention;
FIG. 3 is a correlation diagram of information to be inverted and observed quantities in an earth surface region in embodiment 2 of the present invention;
fig. 4 is a first calibration schematic in embodiment 3 of the present invention;
fig. 5 is a second calibration diagram according to embodiment 3 of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide a calibration method and a calibration system for a reflection point of a terrestrial satellite-borne GNSS (global navigation satellite system) reflection signal, which can be used for correcting the reflection point of a mirror surface determined based on a spherical model or an ellipsoidal model by utilizing elevation data and improving the measurement accuracy of the terrestrial satellite-borne GNSS.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Example 1
As shown in fig. 2, the present embodiment provides a method for calibrating a specular reflection point of a terrestrial satellite-borne GNSS reflection signal, including:
step 101: acquiring an initial specular reflection point set; the initial mirror reflection point set is determined by the global navigation satellite system to enable the land area to be measured to be equivalent to a spherical model or an ellipsoidal model;
step 102: acquiring any initial specular reflection point as a current initial specular reflection point;
step 103: determining a current approximate reflecting surface according to elevation data of a current initial specular reflection point;
step 103 comprises: constructing a current nine-square grid by taking a current initial specular reflection point as a center and a preset distance as a side length; determining the average elevation of areas corresponding to all edge grids in the current nine-grid; the edge lattices are lattices except the lattices in which the current initial specular reflection points are positioned in the nine-square lattices; and determining the plane of the average elevation as the current approximate reflecting surface.
Step 104: determining a decision variable of a current initial specular reflection point according to the current approximate reflection surface;
step 104 comprises: obtaining an incident angle theta of an incident signal i (ii) a Obtaining the emergent angle theta of the emergent signal r (ii) a Determining a first included angle phi between the projection of the incident signal on the current approximate reflecting surface and the east direction i (ii) a Determining a second included angle phi between the projection of the emergent signal on the current approximate reflecting surface and the east direction r (ii) a According to the formula psi ═ theta according to the incident angle, the exit angle, the first angle and the second angle i -θ r |+r|φ i -φ r Determining a judgment variable of a current initial specular reflection point; wherein psi is the judgmentDetermining a variable; r is a penalty coefficient; r is more than 0 and less than 1.
Step 105: and calibrating the current initial specular reflection point according to the decision variable.
Step 105 comprises: and judging whether the judgment variable is smaller than a judgment threshold value or not to obtain a first judgment result. If the first judgment result is yes, the current initial specular reflection point is determined to be the land mirror surface reflection point.
And if the first judgment result is negative, calibrating the current initial specular reflection point according to all the edge lattices in the current nine-square lattice.
Calibrating the current initial specular reflection point according to all edge cells in the current nine-square cell includes: determining the middle points of all edge lattices in the current nine-square lattice as pseudo mirror reflection points; determining a decision variable of each pseudo mirror reflection point as a pseudo decision variable according to the current approximate reflection surface; judging whether the minimum false judgment variable is smaller than a judgment threshold value or not to obtain a second judgment result; if the second judgment result is yes, determining the pseudo mirror surface reflection point corresponding to the minimum pseudo judgment variable as a land mirror surface reflection point; and if the second judgment result is negative, determining that the current initial specular reflection point is a diffuse reflection-like point.
After step 105, further comprising: and (4) returning to the step 103 until the initial specular reflection point set is passed, so as to obtain a terrestrial mirror surface reflection point set and a diffuse reflection point-like set.
Example 2
The embodiment provides a calibration method with high algorithm efficiency and small result deviation, and the method is used for creating an iterative algorithm for mirror point search by utilizing a GNSS-R geometric relation and a nonlinear programming method based on an included angle and a shortest path respectively, so that the estimation of the position of a real mirror reflection point is realized.
Step 1: obtaining the most important observed quantity of the satellite-borne GNSS-R: the Delay-Doppler two-dimensional variable of the bistatic scattering-related power, i.e. Delay Doppler Map (DDM), is shown in the formula:
here, the number of the first and second electrodes,<|Y(τ,f)| 2 >representing the correlation power, T, between the reflected signal component with time delay tau and Doppler frequency f in the GNSS multipath reflected signal and the local pseudo-random code of the receiver i Is the coherent integration time of the receiver; λ is the carrier wavelength of the GNSS signal; p t Is the GNSS satellite transmit power; g t Transmitting antenna gain for GNSS satellites; g r (ρ) is the GNSS reflected signal receiving antenna gain; r 0 (p) is the range R of the transmitter to the ground 1 (ρ) is the ground-to-receiver range;
when the direct signal is p polarization, the reflected signal adopts a bistatic radar scattering coefficient when q polarization is received; a denotes a signal irradiation area.
Step 2: the DDM contains the information of the reflecting surface to be inverted. And establishing a relation between the information to be inverted in the earth surface area and the DDM characteristic parameters (observed quantity) by combining the equal time delay area and the equal Doppler area in the node. The mapping relationship is as shown in fig. 3.
And 3, step 3: setting the time delay of the maximum power point of the satellite-borne GNSS-R DDM as tau max Doppler shift of D max . Then the time delay of the reflection point S is defined as:
τ s ＝τ dir -δP (2)
wherein tau is s Code delay, tau, for GNSS signal arrival at point s dir For the code delay of the direct signal, δ P is the code delay of the direct reflected signal:
in the formula (I), the compound is shown in the specification,
a GNSS satellite vector for the earth-centered transmit signal,
the GNSS-R satellite vectors of the received signals,
the vector of the initial specular reflection point S is the physical meaning of δ P, which is the difference between the reflected signal path and the direct path. Wherein
Can represent that:
in the formula (I), the compound is shown in the specification,
the vectors with corresponding points of latitude (lat ') and longitude offset (lon') on an earth ellipsoid model (such as WGS84) are shown, and Δ H is the elevation given by the DEM model.
The time delay from the initial specular reflection point S to the power maximum point can thus be defined as:
δτ＝τ max -τ s (5)
and 4, step 4: doppler shift D defining initial specular reflection point S s ：
D s ＝D R +D T +D clk (6)
In the formula, D T For Doppler shifts caused by GNSS satellite motion, D R For frequency shifts caused by GNSS-R satellite motion, D clk Is the doppler shift caused by the offset in the satellite. D T And D R Can be calculated by equations (7) and (8), respectively:
in the formula (I), the compound is shown in the specification,
for the speed of the GNSS-R receiver,
the speed of the GNSS satellite, f the carrier frequency of the GNSS signal, and c the speed of light.
The unit vector of the GNSS-R satellite motion at the current approximate reflecting surface RST,
a unit vector of the GNSS satellite moving on the current approximate reflecting surface RST, wherein:
thus, the doppler difference of the reflection point S with respect to the DDM power maximum point can be expressed as:
δD＝D max -D S (11)
and 5: the ground is divided into grids by considering the influence of the terrain, and S1, S2, S3 and S4 are respectively adjacent points (pseudo mirror reflection points) of the reflection point S in four directions of north, south and east-west, as shown in FIGS. 4-5.
In FIGS. 4-5, P 1 An incident vector of the GNSS signal; p 2 Is a GNSS signal exit vector, P' 1 ，P′ 2 Is the projection of both on the real ground surface. Since the position of the initial specular reflection point S is calculated according to the elliptical model, the Snell' S law is not satisfied (i.e., θ is not satisfied) i ≠θ r )。
For the purpose of analysis, a reference coordinate system ENU is defined with the initial specular reflection point S as the center,
a unit vector pointing in the east direction;
a unit vector indicating a north direction;
unit vector in zenith direction:
incident vector P 1 And the emission vector P 2 Reflection plane projected into ENU coordinate system:
P′ 1,E 、P′ 1,N and P' 1,U Respectively represent incident vectors P 1 And the incident vectors projected to the E coordinate axis, the N coordinate axis and the coordinate system axis.
P′ 2,E 、P′ 2,N And P' 2,U Respectively represent incident vectors P 2 And the incident vectors projected to the E coordinate axis, the N coordinate axis and the coordinate system axis.
Further, the theta is obtained i ，θ r ，φ i And phi r ：
Step 6: based on theta i ，θ r ，φ i And phi r Establishing an iterative algorithm to correct the reflection point of the land mirror surface, and describing the steps as follows:
the algorithm comprises the following steps:
1.1) as shown in the figures 4-5, the first initial pseudo-specular reflection point S point in the data set is acquired, the average elevation of eight adjacent units is calculated by using the DEM, and an approximate reflecting surface is acquired. Computing normal, various angles (including theta) based on the approximated reflecting surface i ，θ r ，φ i And phi r )。
1.2) define the decision variable ψ ═ θ i -θ r |+r|φ i -φ r And l, r is more than 0 and less than 1, which is a penalty coefficient. Let T 0 To decide the threshold, if psi s ＞T 0 And calculating psi values of the center points of the eight neighborhood units of the S point.
Otherwise, the loop is terminated, the point S is determined to be the best approximation of the specular reflection point, and the point is collected into the specular reflection set.
1.3) taking minimum decision variable psi 'of eight neighborhoods, if psi' < psi s This point is taken as a new S point. Otherwise, the loop is terminated and the point data is taken into the non-specular reflection set.
1.4) taking the next pseudo-specular reflection point S point in the data set, and returning to the step 1.1). If all the pseudo mirror reflection points S in the data set are operated, finishing the algorithm to obtain a mirror reflection set and a similar diffuse reflection set, and subsequently adopting different algorithms for the two sets when inverting the soil humidity or vegetation parameters and determining different precision levels.
And a second step of algorithm:
2.1) preprocessing the DDM of the reflection events in the similar diffuse reflection set, eliminating noise or overcorrection influence, and calculating the total energy of the similar diffuse reflection set
Wherein M is i,j Representing the value of the i th row and j th column element of ddm.
2.2) setting the energy threshold E 0 Ratio _ k × E, (0 < ratio _ k < 1), and the element value M in DDM i,j Sorting is carried out, the first M element values with the energy sum larger than the threshold value are calculated and are recorded as [ M ] 0 ,M 1 ,...,M m ]I.e. by
Wherein M is 0 Is the maximum value of the DDM element, and m is the minimum value satisfying the condition. Wherein the parameter ratio k is a fraction greater than 0 and less than 1.
2.3) statistics of [ M 0 ,M 1 ,...,M m ]Probability of occurrence of position distribution, M 0 The maximum probability interval where the position is located is the main reflected energy area.
And finally obtaining the corrected reflection point of the specular reflection set and the reflection energy main area of the diffuse reflection-like set. The main reflected energy area is used for determining the main detected area, and then an inversion model is established.
Example 3
The embodiment provides a calibration system for a specular reflection point of a terrestrial satellite-borne GNSS reflection signal, comprising:
the initial specular reflection point set acquisition module is used for acquiring an initial specular reflection point set; the initial specular reflection point set is determined by the global navigation satellite system to enable the land area to be measured to be equivalent to a spherical model or an ellipsoidal model.
And the current initial specular reflection point acquisition module is used for acquiring any initial specular reflection point as the current initial specular reflection point.
And the current approximate reflecting surface determining module is used for determining the current approximate reflecting surface according to the elevation data of the current initial specular reflection point.
And the decision variable determining module is used for determining the decision variable of the current initial specular reflection point according to the current approximate reflecting surface.
And the calibration module is used for calibrating the current initial specular reflection point according to the judgment variable.
Wherein the current approximate reflecting surface determining module includes: the current nine-grid construction unit is used for constructing a current nine-grid by taking the current initial specular reflection point as the center and a preset distance as the side length; the average elevation determining unit is used for determining the average elevation of areas corresponding to all the edge grids in the current nine-square grid; the edge lattices are lattices except the lattices in which the current initial specular reflection points are positioned in the nine-square lattices; and the current approximate reflecting surface determining unit is used for determining the plane where the average elevation is located as the current approximate reflecting surface.
Specifically, the decision variable determining module includes: an incident angle acquiring unit for acquiring an incident angle theta of the incident signal i (ii) a An exit angle acquisition unit for acquiring an exit angle theta of the exit signal r (ii) a A first included angle determining unit for determining a first included angle phi between the projection of the incident signal on the current approximate reflecting surface and the east direction i (ii) a A second included angle determining unit for determining a second included angle phi between the projection of the emergent signal on the current approximate reflecting surface and the east direction r (ii) a A decision variable determining unit for determining a first angle and a second angle according to the formula psi ═ theta i -θ r |+r|φ i -φ r Determining a judgment variable of a current initial specular reflection point; wherein psi is a decision variable; r is a penalty coefficient; r is more than 0 and less than 1.
Further, the calibration module includes: the first judgment unit is used for judging whether the judgment variable is smaller than the judgment threshold value or not to obtain a first judgment result; if the first judgment result is yes, calling a terrestrial mirror surface reflection point determining unit; if the first judgment result is negative, calling a calibration unit; the land mirror surface reflection point determining unit is used for determining the current initial mirror surface reflection point as a land mirror surface reflection point; and the calibration unit is used for calibrating the current initial specular reflection point according to all the edge grids in the current nine-square grid.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In summary, this summary should not be construed to limit the present invention.
Claims (10)
1. A calibration method for a specular reflection point of a terrestrial satellite-borne GNSS reflection signal is characterized by comprising the following steps:
acquiring an initial specular reflection point set; the initial specular reflection point set is determined by the global navigation satellite system to enable the land area to be measured to be equivalent to a spherical model or an ellipsoidal model;
acquiring any initial specular reflection point as a current initial specular reflection point;
determining a current approximate reflecting surface according to elevation data of a current initial specular reflection point;
determining a decision variable of the current initial specular reflection point according to the current approximate reflecting surface;
and calibrating the current initial specular reflection point according to the decision variable.
2. The method for calibrating the specular reflection point of the terrestrial satellite-borne GNSS reflection signal according to claim 1, wherein the determining the current approximate reflection surface according to the elevation data of the current initial specular reflection point comprises:
constructing a current nine-square grid by taking the current initial specular reflection point as a center and a preset distance as a side length;
determining the average elevation of areas corresponding to all edge grids in the current nine-square grid; the edge grids are grids except the grid where the current initial specular reflection point is located in the nine-square grid;
and determining the plane where the average elevation is located as the current approximate reflecting surface.
3. The method according to claim 1, wherein the determining the decision variable of the current initial specular reflection point according to the current approximate reflecting surface comprises:
obtaining an incident angle theta of an incident signal i ；
Obtaining the emergent angle theta of the emergent signal r ；
Determining a first included angle phi between the projection of the incident signal on the current approximate reflecting surface and the east direction i ；
Determining a second included angle phi between the projection of the emergent signal on the current approximate reflecting surface and the east-ward direction r ；
According to the incident angle, the exit angle, the first included angle and the second included angle, according to a formula psi ═ theta i -θ r |+r|φ i -φ r Determining a judgment variable of a current initial specular reflection point; wherein psi is a decision variable; r is a penalty coefficient; r is more than 0 and less than 1.
4. The method according to claim 2, wherein the calibrating the current initial specular reflection point according to the decision variable comprises:
judging whether the judgment variable is smaller than a judgment threshold value or not to obtain a first judgment result;
if the first judgment result is yes, determining that the current initial mirror surface reflection point is a land mirror surface reflection point;
and if the first judgment result is negative, calibrating the current initial specular reflection point according to all the edge grids in the current nine-square grid.
5. The method as claimed in claim 4, wherein the calibrating the current initial specular reflection point according to all the edge cells in the current nine-square cell comprises:
determining the middle points of all edge lattices in the current nine-square lattice as pseudo mirror reflection points;
determining a decision variable of each pseudo mirror reflection point as a pseudo decision variable according to the current approximate reflection surface;
judging whether the minimum false judgment variable is smaller than a judgment threshold value or not to obtain a second judgment result;
if the second judgment result is yes, determining a pseudo mirror surface reflection point corresponding to the minimum pseudo judgment variable as a land mirror surface reflection point;
and if the second judgment result is negative, determining that the current initial specular reflection point is a diffuse reflection-like point.
6. The method according to claim 5, further comprising, after calibrating the current initial specular reflection point according to the decision variable:
and (3) current initial specular reflection points and returning to the step of determining a current approximate reflecting surface according to the elevation data of the current initial specular reflection points until the initial specular reflection point set is passed, so as to obtain a terrestrial mirror surface reflection point set and a diffuse reflection point-like set.
7. A system for calibrating specular reflection points of terrestrial satellite-borne GNSS reflected signals comprises:
the initial specular reflection point set acquisition module is used for acquiring an initial specular reflection point set; the initial specular reflection point set is determined by the global navigation satellite system to enable the land area to be measured to be equivalent to a spherical model or an ellipsoidal model;
the current initial specular reflection point acquisition module is used for acquiring any initial specular reflection point as a current initial specular reflection point;
the current approximate reflecting surface determining module is used for determining a current approximate reflecting surface according to the elevation data of the current initial specular reflection point;
a decision variable determining module, configured to determine a decision variable of the current initial specular reflection point according to the current approximate reflecting surface;
and the calibration module is used for calibrating the current initial specular reflection point according to the judgment variable.
8. The system according to claim 7, wherein the current approximate reflecting surface determining module comprises:
the current nine-grid construction unit is used for constructing a current nine-grid by taking the current initial specular reflection point as a center and a preset distance as a side length;
the average elevation determining unit is used for determining the average elevation of areas corresponding to all the edge grids in the current nine-square grid; the edge grids are grids except the grid where the current initial specular reflection point is located in the nine-square grid;
and the current approximate reflecting surface determining unit is used for determining the plane where the average elevation is located as the current approximate reflecting surface.
9. The system of claim 7, wherein the decision variable determining module comprises:
an incident angle acquiring unit for acquiring an incident angle theta of the incident signal i ；
An emergent angle acquiring unit for acquiring emergent angle theta of emergent signal r ；
A first angle determining unit for determining a first angle phi between the projection of the incident signal on the current approximate reflecting surface and the east-ward direction i ；
A second included angle determining unit for determining a second included angle phi between the projection of the emergent signal on the current approximate reflecting surface and the east-pointing direction r ；
A decision variable determining unit for determining a first angle from the incident angle, the exit angle, the first angle and the second angle according to a formula psi ═ theta i -θ r |+r|φ i -φ r Determining a judgment variable of a current initial specular reflection point; wherein psi is a decision variable; r is a penalty coefficient; r is more than 0 and less than 1.
10. The system according to claim 8, wherein the calibration module comprises:
the first judgment unit is used for judging whether the judgment variable is smaller than a judgment threshold value or not to obtain a first judgment result; if the first judgment result is yes, calling a terrestrial mirror surface reflection point determining unit; if the first judgment result is negative, calling a calibration unit;
the land mirror surface reflection point determining unit is used for determining the current initial mirror surface reflection point as a land mirror surface reflection point;
and the calibration unit is used for calibrating the current initial specular reflection point according to all the edge grids in the current nine-square grid.
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| CN116540273B (en) * | 2023-07-05 | 2023-09-19 | 天津大学 | GNSS-R mirror reflection point initial value position determination method and device and electronic equipment |
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