Lunar satellite occlusion analysis method based on moon topographic data

Abstract

The invention discloses a lunar satellite occlusion analysis method based on lunar topographic data, and the method comprises the steps: S1, processing lunar elevation data, and obtaining the topographic data; s2, constructing a terrain elevation angle database according to the processed moon elevation data; s3, determining an orbit of a target satellite, and obtaining orbit parameters to obtain coordinates of the target satellite; s4, calculating an elevation angle and an azimuth angle of the target satellite relative to each lunar elevation data grid at each sampling moment; and S5, querying the terrain database through the azimuth angle between the target satellite and the current grid, and judging whether the current grid is shielded by the terrain at the current moment. According to the method, the terrain elevation angle database is quickly constructed by using the moon DEM data, and the time consumption for constructing the terrain elevation angle database is low. No matter how the satellite orbits and the number change, the terrain elevation angle database only needs to be constructed once, and the shielding condition of the lunar terrain on the lunar satellite can be quickly judged only by calculating the azimuth angle and the elevation angle of the terrain grid according to the coordinates of the satellite subsequently.

Description

Technical Field

[0001] The present invention relates to the field of aerospace, and in particular to a lunar satellite occlusion analysis method based on lunar terrain data. Background Art

[0002] The lunar south pole has abundant water ice resources, and the permanent shadow area at the lunar south pole has high exploration value. In order to support lunar exploration and utilization activities, the lunar navigation satellite system (LNSS) was proposed as an important lunar navigation and positioning system. LNSS can provide high-precision, real-time navigation and positioning (PNT) services for lunar probes, lunar bases, and future lunar mining activities, and has important strategic and economic value. Due to the lack of atmosphere, there are many impact craters on the lunar surface, which make the lunar surface geographical environment complex and changeable. If it is located in a deeper impact crater, it is likely that the satellite signal cannot be received. Therefore, satellite visibility calculation is required to determine whether the satellite signal at a certain moment is blocked by the terrain and whether it can be observed. By combining actual terrain data, the real satellite signal environment can be better simulated, so as to evaluate the performance of LNSS in actual scenarios and improve the credibility and practicality of the evaluation results.

[0003] There is no research on evaluating navigation performance in combination with terrain analysis, but there are studies that analyze the terrain of the lunar landing area and simulate communication between the Earth and the landing area. In addition, there are studies that analyze the lighting conditions in the lunar South Pole region in combination with elevation data. The difficulties in combining terrain data analysis are: (1) There are currently few literatures on analyzing satellite signal occlusion based on lunar terrain data, which brings difficulties to the exploration and research of technical routes. (2) The sparse sampling points on the lunar surface reduce the availability of the calculation results and the reference is not high. (3) Increasing the density of sampling points can improve the reliability of the results, but at the same time it will increase the time loss of data processing, intermediate result calculation, and occlusion analysis and judgment, greatly increasing the time cost.

[0004] In view of the difficulties of the existing technology, a method for quickly realizing the occlusion analysis of lunar satellites based on lunar terrain data is proposed. This method introduces data such as elevation angle and azimuth angle to determine whether the satellite signal is blocked. At the same time, it introduces the terrain elevation angle database to improve the reliability of the simulation results and realize high-resolution satellite signal occlusion analysis based on lunar terrain data. The terrain elevation angle database only needs to be built once, which can reduce the time loss of terrain occlusion analysis and judgment, and realize rapid analysis. Summary of the invention

[0005] The purpose of the present invention is to overcome the above defects. The present invention provides a lunar satellite occlusion analysis method based on lunar terrain data. Based on the Kepler orbit parameters of the LNSS satellite and the lunar terrain elevation data, a terrain elevation database is constructed to quickly realize satellite signal occlusion judgment based on terrain. To achieve the above purpose, the technical solution of the present invention includes:

[0006] A lunar satellite occlusion analysis method based on lunar topography data, characterized by comprising:

[0007] S1: Process the lunar elevation data to obtain terrain data;

[0008] S2: Construct terrain elevation database based on the processed lunar elevation data;

[0009] S3: Determine the orbit of the target satellite and obtain orbital parameters to obtain the coordinates of the target satellite at different times;

[0010] S4: Calculate the elevation and azimuth of the target satellite at each sampling moment relative to each grid of lunar elevation data;

[0011] S5: querying the terrain database through the azimuth between the target satellite and the current grid to determine whether the current grid is blocked by the terrain at the current moment.

[0012] A further improvement of the present invention is that in step S1, the process of processing the lunar elevation data includes: clipping the lunar elevation data, and resampling the clipped data to a target resolution.

[0013] A further improvement of the present invention is that: in the process of constructing the terrain elevation database, for each grid of the lunar elevation data, the grid is taken as the central grid, and a calculation direction is selected at every predetermined angle interval; for each grid passed by the calculation direction, the grid is divided into a first interval, a second interval and a third interval according to the distance between the grid and the central grid;

[0014] For the first interval, the elevation angles between the central grid and the grids in the interval are calculated one by one;

[0015] For the second interval, the elevation angle between the central grid and the grids of the interval is calculated for every two grids;

[0016] For the third interval, the elevation angle between the central grid and the grids of the interval is calculated for every four grids;

[0017] The largest elevation angle among the above three intervals is taken as the maximum elevation angle of the central grid in this direction and recorded in the terrain elevation angle database;

[0018] Among them, the first interval: the distance from the central grid is 0~5km; the second interval: the distance from the central grid is 5~100km; the third interval: the distance from the central grid is 100~r; where r is the maximum distance, the value is 200 or 250km.

[0019] A further improvement of the present invention is that the process of calculating the elevation angle between the central grid and a grid in the calculation direction comprises the following steps:

[0020] The lunar geographic coordinate system coordinates of the central grid expressed in the lunar geographic coordinate system are converted to the lunar fixed coordinate system, and the expression is:

[0021]

[0022] Where: L, B are the geographical longitude and latitude of the central grid, h is the elevation, and R is the radius of the lunar reference model;

[0023] In the same way, the lunar geographic coordinate system coordinates of the grid as the target in the calculation direction are converted into the lunar fixed coordinate system (x (s) ,y (s) ,z (s) ) T ;

[0024] In the lunar coordinate system, the observation vector of the grid with respect to the central grid is calculated from the coordinates of the central grid and the coordinates of the grid as the target:

[0025]

[0026] Where: (x, y, z) T is the lunar coordinate system coordinate of the central grid, (x (s) ,y (s) ,z (s) ) T is the lunar coordinate system coordinate of the grid as the target;

[0027] The observations in the lunar fixed coordinate system are converted to the lunar station center coordinate system, and the expression is:

[0028]

[0029] Where: are all column vectors, and their calculation formulas are as follows:

[0030]

[0031] Where: L is the geographic coordinate longitude of the central grid, × is the outer product operation of the matrix, x, y, z are the lunar coordinates of the central grid;

[0032] The observed values ​​(Δe, Δn, Δu) of the grid relative to the central grid in the station center coordinate system are obtained by using the geographic coordinates of the central grid and the lunar coordinates of the grid as the target. T Then, use the following formula to calculate the elevation angle θ:

[0033]

[0034] A further improvement of the present invention is that for the lunar elevation data represented by the lunar geographic coordinate system and the coordinates of the satellite represented by the lunar fixed coordinate system, the process of calculating the elevation angle and azimuth angle of the target satellite relative to a grid of the lunar elevation data includes the following steps:

[0035] The grid is used as the current terrain grid, and the lunar geographic coordinate system coordinates of the current terrain grid are converted to the lunar solid coordinate system. The expression is:

[0036]

[0037] Where: L, B are the geographic longitude and latitude of the current terrain grid, h is the elevation, and R is the radius of the lunar reference model;

[0038] In the lunar coordinate system, the observation vector of the target satellite relative to the current terrain grid is calculated from the current terrain grid coordinates and satellite coordinates:

[0039]

[0040] Where: 9x,y,z) T is the lunar coordinate system coordinate of the current terrain grid, 9x (s) ,y (s) ,z (s) ) T is the satellite's lunar-fixed coordinate system coordinate;

[0041] The observations in the lunar fixed coordinate system are converted to the lunar station center coordinate system, and the expression is:

[0042]

[0043] Where: are all column vectors, and their calculation formulas are as follows:

[0044]

[0045] Where: L is the geographic coordinate longitude of the current terrain grid, × is the outer product operation of the matrix, x, y, z are the lunar coordinates of the current terrain grid;

[0046] Using the geographic coordinates of the current terrain grid and the satellite's lunar coordinates, we can obtain the satellite's observation values ​​(Δe, Δn, Δu) relative to the current terrain grid in the station center coordinate system. T Then, use the following formula to calculate the elevation angle θ and azimuth angle Δ:

[0047]

[0048] The beneficial effects of the present invention include: the method uses lunar DEM data to quickly construct a terrain elevation database, and the construction of the terrain elevation database takes less time. Regardless of how the satellite orbit and number change, the terrain elevation database only needs to be constructed once, and subsequently, the azimuth and elevation of the terrain grid can be calculated based on the satellite coordinates to quickly determine the obstruction of the lunar satellite by the lunar terrain. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a technical route flow chart of the method of the present invention;

[0050] Figure 2 Schematic diagram of the lunar fixed coordinate system (left), schematic diagram of the lunar surface station center coordinate system (right, the X, Y, and Z axes of the black arrows represent the lunar fixed coordinate system, and the X, Y, and Z axes of the red, green, and blue arrows represent the lunar surface station center coordinate system);

[0051] Figure 3 The elevation angle changes at different distances for the same height difference. Left: Height difference 0.1km;

[0052] Right: height difference 0.5km;

[0053] Figure 4 A specific flow chart of the method of the present invention;

[0054] Figure 5 A terrain grid that passes through the center grid at different locations at certain angle intervals;

[0055] Figure 6 It is a visualization of satellite occlusion of the same constellation satellites in adjacent terrain grids at the same time. The radius represents the elevation angle and the arc is the azimuth angle.

[0056] Figure 7 The average number of visible satellites (Ave-NVS) for 8 satellites of different constellations at different times of the day in the lunar south polar region without or with terrain occlusion analysis;

[0057] Figure 8 is a flow chart of an existing method;

[0058] Fig. 9 The computer configuration used for comparison of the two methods. DETAILED DESCRIPTION

[0059] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0060] It should be noted that the illustrations provided in the following embodiments are only used to illustrate the basic concept of the present invention in a schematic manner, and thus the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0061] like Figure 1 As shown, an embodiment of the present invention includes a lunar satellite occlusion analysis method based on lunar terrain data: first, data preparation is performed: (1) The public lunar elevation data (DEM) is processed to obtain the required terrain data. (2) The satellite orbit to be simulated is determined, the orbit parameters are obtained, and the coordinates of all orbiting satellites at different times are obtained through orbit simulation software. (3) Then, a terrain elevation database is constructed based on the processed DEM data, and the elevation and azimuth of the satellite relative to each grid of the DEM data at each sampling moment are calculated. Finally, the terrain database is queried through the azimuth of the satellite and the current grid to determine whether the current grid is blocked by the terrain at the current moment.

[0062] Calculation of elevation and azimuth

[0063] For the lunar coordinate system, this method mainly uses three different coordinate systems: lunar geographic coordinate system, lunar solid coordinate system, and lunar station center coordinate system. Lunar geographic coordinate system: The position of a point on the lunar surface is expressed by longitude L, latitude B and elevation h. The lunar geographic coordinate system is obtained by processing DEM data. Lunar solid coordinate system: A Cartesian rectangular coordinate system is used, with the lunar center of mass as the origin, the lunar equatorial plane as the basic plane, the Z axis perpendicular to the basic plane pointing to the North Pole, and the X axis pointing to the longitude origin in the equatorial plane. Figure 2 The left figure in the figure shows the coordinate axes of the lunar fixed coordinate system. The satellite coordinates obtained from the simulation software are the coordinates in the lunar fixed coordinate system. Lunar station center coordinate system: The position of the LNSS station established on the moon is taken as the origin, and the tangent plane of the lunar reference ellipsoid passing through the station position is taken as the basic plane. The Z axis coincides with the normal at the station and points in the opposite direction of the lunar center of mass. The X axis points to the east of the moon in the tangent plane, and the Y axis points to the north of the moon in the tangent plane. Figure 2The right picture is a schematic diagram of the lunar station center coordinate system.

[0064] The process of obtaining the elevation and azimuth of a target satellite relative to a grid of lunar elevation data consists of the following steps:

[0065] The grid is used as the current terrain grid, and the lunar geographic coordinate system coordinates of the current terrain grid are converted to the lunar solid coordinate system. The expression is:

[0066]

[0067] Where: L, B are the geographic longitude and latitude of the current terrain grid, h is the elevation, and R is the radius of the lunar reference model;

[0068] In the lunar coordinate system, the observation vector of the target satellite relative to the current terrain grid is calculated from the current terrain grid coordinates and satellite coordinates:

[0069]

[0070] Where: (x, y, z) T is the lunar coordinate system coordinate of the current terrain grid, (x (s) ,y (s) ,z (s) ) T is the satellite's lunar-fixed coordinate system coordinate;

[0071] The observations in the lunar fixed coordinate system are converted to the lunar station center coordinate system, and the expression is:

[0072]

[0073] Where: are all column vectors, and their calculation formulas are as follows:

[0074]

[0075] Where: L is the geographic coordinate longitude of the current terrain grid, β is the outer product operation of the matrix, x, y, z are the lunar coordinates of the current terrain grid;

[0076] Using the geographic coordinates of the current terrain grid and the satellite's lunar coordinates, we can obtain the satellite's observation values ​​(Δe, Δn, Δu) relative to the current terrain grid in the station center coordinate system. T Then, use the following formula to calculate the elevation angle θ and azimuth angle α:

[0077]

[0078] In the process of constructing the terrain elevation database, it is necessary to calculate the elevation angle between the central grid and a grid in the calculation direction (the grid as the target). The process of calculating the elevation angle is similar to the above process (calculating the elevation angle between the grid and the target satellite). It is necessary to convert the coordinates of the central grid and the grid as the target in the calculation direction from the lunar geographic coordinate system to the lunar fixed coordinate system; in the lunar fixed coordinate system, calculate the observation vector between the two; convert the observation in the lunar fixed coordinate system to the lunar station center coordinate system, and then the elevation angle θ can be calculated in the same way.

[0079] Rapid construction of terrain elevation database

[0080] To construct a terrain elevation database, it is necessary to determine the terrain grids that pass through a certain terrain grid in any direction within a distance r (using DDA and other related algorithms), and calculate the maximum elevation angle between the center grid and the grids that pass through in any direction, and repeat this process at a certain angle interval until all directions within a 360° range around the center grid are covered. The same operation is performed on all grids in the target area to obtain a database of the maximum elevation angles of all terrain grids in any direction.

[0081] In order to improve the speed of building the terrain elevation database: the selection of the maximum distance r can be adjusted. For a terrain grid on the lunar surface, the farthest distance to the horizon is 300km. The usual practice is to select this value as the value of r, then determine all grids within the distance r in this direction, and then calculate the elevation angle one by one; but calculating the elevation angle requires coordinate conversion, which is time-consuming. Calculating one by one takes too much time, so there is room for optimization.

[0082] Since the elevation angle with respect to the center grid is smaller the farther away the same elevation is from the center grid, the elevation angle should be calculated more intensively at close distances, and the frequency of calculating the elevation angle should be lower at long distances. In order to determine the specific values ​​of the distances, this method uses a mathematical model to describe the influence of elevation and distance on the elevation angle. The lunar surface is approximated as a plane within the lunar horizon distance, and the inverse tangent function is used to calculate the elevation angle of the surrounding terrain grid and the center grid:

[0083]

[0084] Where: Δh represents the height difference, Δd represents the horizontal distance. This formula is used to qualitatively explain the relationship between elevation angle and distance. The influence of elevation angle within the maximum visible distance of 300km for the same height difference is as follows: Figure 3 As shown. Figure 3 It can be seen that no matter how the height difference changes, the image can still be divided into three parts according to the amplitude of the elevation angle change. The first part has the largest amplitude change, and the corresponding distance is very close to the center grid; the second part has a smaller amplitude change and is closer to the center grid; the third part has a slight amplitude change and is the farthest from the center grid.

[0085] Therefore, in this embodiment, in the process of constructing the terrain elevation database, for each grid of the lunar elevation data, the grid is taken as the central grid, and a calculation direction (a ray starting from the central grid) is selected at every predetermined angle interval; for each grid passed by the calculation direction, the grid is divided into a first interval, a second interval, and a third interval according to its distance from the central grid;

[0086] For the first interval, the elevation angles between the central grid and the grids in the interval are calculated one by one;

[0087] For the second interval, the elevation angle between the central grid and the grids of the interval is calculated for every two grids;

[0088] For the third interval, the elevation angle between the central grid and the grids of the interval is calculated for every four grids;

[0089] The largest elevation angle among the above three intervals is taken as the maximum elevation angle of the central grid in this direction and recorded in the terrain elevation angle database;

[0090] The first interval: the distance from the central grid is 0 to 5 km; the second interval: the distance from the central grid is 5 to 100 km; the third interval: the distance from the central grid is 100 to r (r is the maximum distance, determined by Figure 3 It can be seen that the appropriate value of r can be 200 or 250 km). This method can effectively reduce the amount of calculation for building a terrain elevation database.

[0091] The technical solution of this embodiment uses lunar DEM data to quickly build a terrain elevation database, which takes less time to build. Regardless of how the satellite orbit and number change, the terrain elevation database only needs to be built once, and the subsequent calculation of the azimuth and elevation of the terrain grid based on the satellite coordinates can quickly determine the obstruction of the lunar terrain to the lunar satellite.

[0092] like Figure 4 As shown, in a specific embodiment, the method of the present invention comprises the following steps:

[0093] (1) Determine the latitude and longitude range of the target area, and crop the full-month data to obtain the elevation data of the area of ​​interest. Resample to obtain the appropriate resolution as needed or select the terrain data of the required resolution for download to obtain the processed terrain data.

[0094] (2) Constructing a terrain elevation database: Determine the appropriate maximum distance r, use DDA and other related algorithms to determine the grids that the central grid passes through in any direction within the distance r, divide the distance r into three sections (from the inside to the outside, the first section, the second section, and the third section), adopt different elevation angle calculation methods according to different distances, and save the maximum elevation angle in the current direction and the current direction angle in the terrain elevation database (the database is two-dimensional).

[0095] (3) The lunar coordinates of the satellite at each time are obtained through simulation software, and the azimuth and elevation angles (θ) of all orbiting satellites and all terrain grids are calculated.

[0096] (4) The maximum elevation angle of the terrain in that direction is queried in the terrain elevation database through the azimuth between the satellite and all terrain grids, and whether the satellite is blocked by the terrain is determined by comparison: if θ is less than or equal to the maximum elevation angle, it is blocked; otherwise, it is not blocked.

[0097] In different cases, the visualization results of terrain grids passing through the center grid in all directions within the distance r are obtained at a certain angle interval (interval: 1 degree in the angle system). Figure 5 shown. Figure 5 In the figure, the maximum distance is r = 200 km. The depth of gray indicates the elevation value, and the other colors are the terrain grids that the central grid passes through in r in all directions.

[0098] Figure 6 This is a visualization of satellite obstruction of the same constellation satellites at the same time in adjacent terrain grids. The radius represents the elevation angle and the arc represents the azimuth angle. (The position of Figure a is directly above Figure b. The total number of constellation satellites is 8. The number represents the satellite serial number. Blue means the satellite is not obstructed by terrain, and gray means the satellite is obstructed by terrain). Figure 6 This shows that even the adjacent terrain grids are blocked by terrain, which is very different. Therefore, it is necessary to analyze and judge the terrain blocking of lunar satellites.

[0099] Figure 7 The average number of visible satellites (Ave-NVS) for 8 satellites of different constellations at different times of the day in the lunar south polar region without or with terrain occlusion analysis. (Figure a: constellation 1 without terrain occlusion analysis, Figure b: constellation 2 without terrain occlusion analysis, Figure c: constellation 1 with terrain occlusion analysis, Figure d: constellation 2 with terrain occlusion analysis)

[0100] Depend on Figure 7 It can be seen that satellites orbiting the moon are easily blocked by terrain near lunar craters, and terrain blockage analysis based on lunar DEM data is important. Rapidly implementing lunar satellite blockage analysis based on lunar terrain data can greatly save time and cost, which is of great significance for the simulation analysis of lunar LNSS performance.

[0101] Comparison with general methods:

[0102] Figure 8 The general approach shown requires first calculating the azimuth (denoted as α) and elevation between each satellite and each terrain grid, then determining the terrain grids that pass through the current terrain grid in the α direction within a distance r, calculating the elevation angle between the current terrain grid and the terrain grids that pass through the α direction, and finding the maximum value of these elevation angles, and finally comparing it with the elevation angle between the satellite and the current terrain grid to determine the occlusion status.

[0103] In the 70S-90S and 180W-180E regions, the same processed DEM data (115,200 terrain grids), the same number of satellites, orbital parameters, and quantity (4 orbits, 8 satellites) were used. Fig. 9 Computers with the same configuration as shown.

[0104] This method takes 4.534 hours to construct the terrain database, 0.35 hours to calculate the elevation and azimuth angles (α) between the satellite and the terrain grid, and 3.2 hours to determine the occlusion state and save the results, for a total of 8.048 hours.

[0105] General method: Calculate the elevation angle and azimuth angle (α) between the satellite and the terrain grid: 0.35h, calculate the elevation angle of the terrain grid passing through the α direction: 28.183h, determine the occlusion status and save the result: 3.2h, a total of 31.733h.

[0106] The accuracy of the results of the two methods is almost exactly the same. At the same time, the construction of the terrain elevation database is one-time, and this method has obvious advantages.

[0107] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A lunar satellite occlusion analysis method based on lunar terrain data, characterized in that include: S1: Process the lunar elevation data to obtain terrain data; S2: Construct terrain elevation database based on the processed lunar elevation data; S3: Determine the orbit of the target satellite and obtain orbital parameters to obtain the coordinates of the target satellite at different times; S4: Calculate the elevation and azimuth of the target satellite at each sampling moment relative to each grid of lunar elevation data; S5: querying the terrain database through the azimuth between the target satellite and the current grid to determine whether the current grid is blocked by the terrain at the current moment.

2. The method for analyzing lunar satellite occlusion based on lunar terrain data according to claim 1, characterized in that: In step S1, the process of processing the lunar elevation data includes: clipping the lunar elevation data, and resampling the clipped data to a target resolution.

3. The method for analyzing lunar satellite occlusion based on lunar terrain data according to claim 1, characterized in that: In the process of constructing the terrain elevation database, for each grid of the lunar elevation data, the grid is taken as the central grid, and a calculation direction is selected at every predetermined angle interval; for each grid passed by the calculation direction, it is divided into the first interval, the second interval and the third interval according to its distance from the central grid; For the first interval, the elevation angles between the central grid and the grids in the interval are calculated one by one; For the second interval, the elevation angle between the central grid and the grids of the interval is calculated for every two grids; For the third interval, the elevation angle between the central grid and the grids of the interval is calculated for every four grids; The largest elevation angle among the above three intervals is taken as the maximum elevation angle of the central grid in this direction and recorded in the terrain elevation angle database; Among them, the first interval: the distance from the central grid is 0 to 5 km; the second interval: the distance from the central grid is 5 to 100 km; the third interval: the distance from the central grid is 100 to r; Where r is the maximum distance, which can be 200 or 250 km.

4. The method for analyzing lunar satellite occlusion based on lunar terrain data according to claim 3, characterized in that: The process of calculating the elevation angle between the central grid and a grid in the calculation direction comprises the following steps: The lunar geographic coordinate system coordinates of the central grid expressed in the lunar geographic coordinate system are converted to the lunar fixed coordinate system, and the expression is: Where: L, B are the geographical longitude and latitude of the central grid, h is the elevation, and R is the radius of the lunar reference model; In the same way, the lunar geographic coordinate system coordinates of the grid as the target in the calculation direction are converted into the lunar fixed coordinate system (x (s) ,y (s) ,z (s) ) T ; In the lunar coordinate system, the observation vector of the grid with respect to the central grid is calculated from the coordinates of the central grid and the coordinates of the grid as the target: Where: (x, y, z) T is the lunar coordinate system coordinate of the central grid, (x (s) ,y (s) ,z (s) ) T is the lunar coordinate system coordinate of the grid as the target; The observations in the lunar fixed coordinate system are converted to the lunar station center coordinate system, and the expression is: Where: are all column vectors, and their calculation formulas are as follows: Where: L is the geographic coordinate longitude of the central grid, × is the outer product operation of the matrix, x, y, z are the lunar coordinates of the central grid; The observed values ​​(Δe, Δn, Δu) of the grid relative to the central grid in the station center coordinate system are obtained by using the geographic coordinates of the central grid and the lunar coordinates of the grid as the target. T Then, use the following formula to calculate the elevation angle θ:

5. The method for analyzing lunar satellite occlusion based on lunar terrain data according to claim 1, characterized in that: For lunar elevation data expressed in the lunar geographic coordinate system and the coordinates of a satellite expressed in the lunar fixed coordinate system, the process of calculating the elevation and azimuth of a target satellite relative to a grid of lunar elevation data includes the following steps: The grid is used as the current terrain grid, and the lunar geographic coordinate system coordinates of the current terrain grid are converted to the lunar solid coordinate system. The expression is: Where: L, B are the geographic longitude and latitude of the current terrain grid, h is the elevation, and R is the radius of the lunar reference model; In the lunar coordinate system, the observation vector of the target satellite relative to the current terrain grid is calculated from the current terrain grid coordinates and satellite coordinates: Where: 9x,y,z) T is the lunar coordinate system coordinate of the current terrain grid, 9x (s) ,y (s) ,z (s) ) T is the satellite's lunar-fixed coordinate system coordinate; The observations in the lunar fixed coordinate system are converted to the lunar station center coordinate system, and the expression is: Where: are all column vectors, and their calculation formulas are as follows: Where: L is the geographic coordinate longitude of the current terrain grid, × is the outer product operation of the matrix, x, y, z are the lunar coordinates of the current terrain grid; Using the geographic coordinates of the current terrain grid and the satellite's lunar coordinates, we can obtain the satellite's observation values ​​(Δe, Δn, Δu) relative to the current terrain grid in the station center coordinate system. T Then, use the following formula to calculate the elevation angle θ and azimuth angle α:

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