Satellite remote sensing image on-board geometric positioning method and system based on ground elevation data

Abstract

The application provides a satellite remote sensing image on-satellite geometric positioning method and system based on ground elevation data, and aims to obtain high-precision longitude and latitude information of a satellite remote sensing image in real time on orbit under the limitation of the calculation and storage capacity of an on-satellite processing system. The application is intended to calculate the actual elevation information of a remote sensing image pixel point on the satellite, and bring the actual elevation information into a direct geometric positioning algorithm to calculate the longitude and latitude of the remote sensing image pixel point. The application stores the global ground elevation data after down-sampling in the on-satellite processing system of the satellite, combines the real-time acquired attitude, position information and remote sensing data parameters, and iterates the direct geometric positioning algorithm multiple times to obtain the relative true elevation value of the pixel point, so as to calculate the longitude and latitude of the pixel point after the elevation information correction. The on-satellite geometric positioning method of the application can configure the positioning precision and adjust the algorithm complexity according to the resource condition of the on-satellite processing system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of satellite remote sensing image on-board processing technology, in particular to a satellite remote sensing image on-board geometric positioning method and system based on ground elevation data. BACKGROUND

[0002] With the continuous progress of aerospace technology, sensor technology and data processing technology, satellite remote sensing technology in China has developed rapidly. Dozens of optical remote sensing satellites of Resource, High Resolution and Mapping Satellite-3 (Mapping Satellite-3) and other series have been launched. By high-precision geometric positioning of satellite remote sensing images to obtain geographic spatial information, accurate mapping for the global has been made, which has effectively supported the scientific development of China's economic construction, environmental protection, disaster warning, national defense and other fields. Corresponding to the large number of satellite groups is the limited satellite-ground transmission capacity and the complicated and slow ground processing technology. Therefore, using on-board processing system to directly generate remote sensing image products and distribute them to the ground has become an important development direction in the field of remote sensing and surveying and mapping.

[0003] As one of the key technologies of on-board processing and the basis for subsequent application, on-board geometric positioning is one of the indispensable links of remote sensing application. According to the principle of photogrammetry, the key to determine the geometric positioning accuracy of satellite remote sensing image depends on the measurement accuracy of on-board position and attitude data, and is also related to ground elevation information. If only the real-time attitude, position and other observation information of satellite in orbit is used for geometric positioning of remote sensing image, the accuracy of remote sensing image positioning on the ground cannot reach a satisfactory level without ground control.

[0004] Therefore, one way to improve the accuracy of on-board geometric positioning is to load ground elevation information into the on-board processing system. However, the existing ground elevation data is too large to be directly loaded into the on-board processing system, and the computing power required by the large amount of data cannot be met. Therefore, how to use ground elevation information in on-board geometric positioning processing is one of the problems to be solved. SUMMARY

[0005] In view of the defects in the prior art, the purpose of the present application is to provide a satellite remote sensing image on-board geometric positioning method and system based on ground elevation data.

[0006] According to the satellite remote sensing image on-board geometric positioning method based on ground elevation data provided by the present application, the method comprises the following steps:

[0007] Step S1: setting the accuracy requirement of on-board geometric positioning, and performing down-sampling on global ground elevation data according to the set accuracy requirement of on-board geometric positioning, and storing the down-sampled data into the on-board processing system;

[0008] Step S2: The on-board processing system receives satellite telemetry data and original remote sensing data in orbit, parses satellite attitude parameters, satellite GPS parameters, satellite time information, and original remote sensing image data values;

[0009] Step S3: According to the obtained satellite attitude parameters, satellite GPS parameters, satellite time information, and original remote sensing image data values, combined with the remote sensing load design parameters, the ground observation incidence angle of the remote sensing image pixel point is calculated;

[0010] Step S4: According to the calculated ground observation incidence angle of the remote sensing image pixel point and the positioning accuracy requirement, the maximum error value D_sub of the height is calculated;

[0011] Step S5: Set the height of the remote sensing image pixel point to the highest altitude of the earth, recorded as the pixel point pre-height Dem1, and calculate the corresponding longitude and latitude, recorded as Lon1, Lat1, find the corresponding height information Dem1' of this point in the global ground height data, calculate the difference D_down1 between Dem1 and Dem1'; if the difference is less than or equal to 0, record the actual height of the pixel point as Dem1, and the pixel point positioning longitude and latitude as Lon1, Lat1, end the calculation; if the difference is greater than 0, trigger step S6;

[0012] Step S6: Calculate the difference between the pixel point pre-height Dem1 and the maximum error value D_sub of the height, recorded as the pixel point post-height Dem2, and determine whether it is greater than 0; if it is greater than 0, trigger step S7, if it is less than or equal to 0, set Dem2 to 0, and trigger step S8;

[0013] Step S7: Calculate the corresponding longitude and latitude based on the pixel point post-height Dem2, recorded as Lon2, Lat2, and find the corresponding height information Dem2' of this point in the global ground height data, calculate the difference D_down2 between Dem2 and Dem2', if the difference is less than or equal to 0, trigger step S8; if the difference is greater than 0, modify the Dem1 value to Dem2, and the D_down1 value to D_down2, and repeat step S6;

[0014] Step S8: According to the calculated Dem1, Dem1', D_down1 and Dem2, Dem2', D_down2 two groups of parameters, the height information of the intersection point is calculated, recorded as the actual height of the pixel point, and step S9 is triggered;

[0015] Step S9: Calculate the corresponding longitude and latitude according to the actual height of the pixel point, and the currently calculated corresponding longitude and latitude are the pixel point positioning longitude and latitude.

[0016] Preferably, the accuracy requirement of the on-board geometric positioning includes:

[0017] The on-board geometric positioning accuracy requirement represents the longitude and latitude error requirement of the on-board processing system for the on-board real-time positioning of the remote sensing image, and should be set according to the load resolution parameter and the positioning purpose of the remote sensing image.

[0018] The on-board geometric positioning accuracy should be greater than the longitude and latitude accuracy of the high-precision global ground elevation data after being down-sampled.

[0019] The high-precision global ground elevation data is global elevation data obtained by radar terrain mapping on a space shuttle.

[0020] Preferably, the step S3 adopts: the calculation method of the ground observation incidence angle of the remote sensing image pixel point is to calculate the included angle between the satellite pixel point ground visual axis vector and the satellite center to the earth center vertical vector.

[0021] The satellite pixel point ground visual axis vector is calculated according to the obtained satellite attitude parameter, satellite GPS parameter, satellite time information and original remote sensing image data value, in combination with the remote sensing load design parameter.

[0022] Preferably, the step S4 adopts:

[0023] D_sub = Prec / tanv;

[0024] Prec is the on-board geometric positioning accuracy requirement; and v is the ground observation incidence angle of the remote sensing image pixel point.

[0025] Preferably, the step S5 adopts: the visual axis of the remote sensing image pixel point in the satellite orbit system is converted to the earth center rotation coordinate system through a conversion matrix, and then the intersection point of the visual axis in the earth center rotation coordinate system and the earth ellipsoid model is calculated, and the longitude and latitude corresponding to the intersection point position are the position information of the pixel point.

[0026] According to the satellite remote sensing image on-board geometric positioning system based on ground elevation data provided by the application, the following are included:

[0027] Module M1: set the accuracy requirement of on-board geometric positioning, and down-sample the global ground elevation data according to the set accuracy requirement of on-board geometric positioning, and store it into the on-board processing system;

[0028] Module M2: the on-board processing system receives satellite telemetry data and original remote sensing data in orbit, and analyzes to obtain satellite attitude parameter, satellite GPS parameter, satellite time information and original remote sensing image data value;

[0029] Module M3: According to the acquired satellite attitude parameters, satellite GPS parameters, satellite time information and original remote sensing image data values, combined with remote sensing load design parameters, the ground observation incidence angle of the remote sensing image pixel point is calculated;

[0030] Module M4: According to the calculated ground observation incidence angle of the remote sensing image pixel point and the positioning accuracy requirement, the maximum error value D_sub of the height is calculated;

[0031] Module M5: The height of the remote sensing image pixel point is set as the highest altitude on the earth, recorded as the pixel point pre-height Dem1, and the corresponding longitude and latitude are calculated, recorded as Lon1 and Lat1, the corresponding height information Dem1' of the point in the global ground height data is searched, and the difference D_down1 between Dem1 and Dem1' is calculated; if the difference is less than or equal to 0, the actual height of the pixel point is recorded as Dem1, and the pixel point positioning longitude and latitude are Lon1 and Lat1, and the calculation is ended; if the difference is greater than 0, module M6 is triggered to execute;

[0032] Module M6: The difference between the pixel point pre-height Dem1 and the maximum error value D_sub of the height is calculated, recorded as the pixel point post-height Dem2, and it is judged whether it is greater than 0; if it is greater than 0, module M7 is triggered to execute, and if it is less than or equal to 0, Dem2 is set as 0, and module M8 is triggered to execute;

[0033] Module M7: The corresponding longitude and latitude based on the pixel point post-height Dem2 are calculated, recorded as Lon2 and Lat2, and the corresponding height information Dem2' of the point in the global ground height data is searched, the difference D_down2 between Dem2 and Dem2' is calculated, and if the difference is less than or equal to 0, module M8 is triggered to execute; if the difference is greater than 0, Dem1 is modified as Dem2, D_down1 is modified as D_down2, and module M6 is repeatedly triggered;

[0034] Module M8: According to the two groups of parameters Dem1, Dem1', D_down1 and Dem2, Dem2', D_down2 calculated, the height information of the intersection point is calculated, recorded as the actual height of the pixel point, and module M9 is triggered;

[0035] Module M9: The corresponding longitude and latitude are calculated according to the actual height of the pixel point, and the currently calculated corresponding longitude and latitude are the pixel point positioning longitude and latitude.

[0036] Preferably, the accuracy requirement of the on-board geometric positioning includes:

[0037] The on-board geometric positioning accuracy requirement represents the longitude and latitude error requirement of the on-board real-time positioning of the remote sensing image by the on-board processing system, which should be set according to the load resolution parameter and the positioning purpose of the remote sensing image;

[0038] The on-board geometric positioning accuracy should be greater than the latitude and longitude accuracy of the high-precision global ground elevation data after down-sampling.

[0039] The high-precision global ground elevation data is global elevation data obtained by radar terrain mapping on a space shuttle.

[0040] Preferably, the module M3 adopts: the calculation method of the ground observation incidence angle of the remote sensing image pixel point is to calculate the included angle between the satellite pixel point ground view axis vector and the satellite center to the earth center vertical vector.

[0041] The satellite pixel point ground view axis vector is calculated according to the obtained satellite attitude parameters, satellite GPS parameters, satellite time information and original remote sensing image data value, in combination with remote sensing load design parameters.

[0042] Preferably, the module M4 adopts:

[0043] D_sub = Prec / tanv;

[0044] Wherein, Prec is the on-board geometric positioning accuracy requirement; v is the ground observation incidence angle of the remote sensing image pixel point.

[0045] Preferably, the module M5 adopts: the view axis of the remote sensing image pixel point in the satellite orbit system is converted to the earth center rotation coordinate system through a conversion matrix, and then the intersection of the view axis in the earth center rotation coordinate system and the earth ellipsoid model is calculated, and the longitude and latitude corresponding to the intersection position are the position information of the pixel point.

[0046] Compared with the prior art, the present application has the following beneficial effects:

[0047] 1. The present application can configure the positioning accuracy according to the resource condition of the on-board processing system, adjust the algorithm complexity, and has certain adaptability to the software and hardware of the on-board processing system.

[0048] 2. The present application can obtain high-precision longitude and latitude information of the satellite remote sensing image in orbit under the condition of no ground control, only using on-board equipment observation information and ground elevation data.

[0049] 3. The present application can control the operation rate within the range of less than the generation rate of the satellite remote sensing image under the premise of ensuring the accuracy, and can meet the real-time requirement of the satellite remote sensing image in-orbit positioning.

[0050] 4. The satellite remote sensing image on-board geometric positioning method based on ground elevation data of the present application is placed in the satellite on-board processing system; and the satellite remote sensing image combined with the ground elevation information realizes high-precision geometric positioning. BRIEF DESCRIPTION OF DRAWINGS

[0051] Other features, objects, and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments thereof, when read in conjunction with the accompanying drawings:

[0052] Figure 1 is a flow chart of the satellite remote sensing image on-board geometric positioning method based on ground elevation data of the present application.

[0053] Figure 2 is a schematic diagram of the satellite remote sensing image on-board geometric positioning method based on ground elevation data of the present application.

[0054] Figure 3 is a schematic diagram for some special terrain of the present application.

[0055] Figure 4 is a running example diagram of the present application. DETAILED DESCRIPTION

[0056] The present application will be described in detail below with specific embodiments. The following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of changes and improvements can be made. These are within the scope of protection of the present application.

[0057] In order to obtain high-precision longitude and latitude information of satellite remote sensing images in real time on orbit under the limitation of the calculation and storage capacity of the on-board processing system, the present application discloses a satellite remote sensing image on-board geometric positioning method and system based on ground elevation data, which aims to calculate the actual elevation information of the remote sensing image pixel points on the satellite, and to bring the actual elevation information into the direct geometric positioning algorithm to calculate the longitude and latitude of the remote sensing image pixel points. The present application stores the global ground elevation data after down-sampling in the satellite on-board processing system, combines the real-time acquired attitude, position information and remote sensing data parameters, and iterates the direct geometric positioning algorithm multiple times to obtain the relative true elevation value of the pixel points, so as to calculate the longitude and latitude of the pixel points corrected by the elevation information. The on-board geometric positioning method of the present application can configure the positioning accuracy and adjust the algorithm complexity according to the resource situation of the on-board processing system. Using the on-board geometric positioning method of the present application, in the case of no ground control, only using the on-board equipment observation information and the ground elevation data, the high-precision longitude and latitude information of the satellite remote sensing image is obtained on orbit.

[0058] Example 1

[0059] According to the satellite remote sensing image on-board geometric positioning method based on ground elevation data provided by the present application, as shown in Figure 1 , it comprises:

[0060] The satellite remote sensing image on-satellite geometric positioning method based on ground elevation data provided by the application is placed in a satellite on-satellite processing system; the on-satellite geometric positioning of the satellite remote sensing image combined with the ground elevation information has the following steps:

[0061] Step one: set the precision requirement of the on-satellite geometric positioning, and according to the requirement, down-sample the high-precision global ground elevation data and store the data in the on-satellite processing system;

[0062] Step two: the on-satellite processing system receives the satellite telemetry data and the original remote sensing data in orbit, analyzes and obtains the satellite attitude parameters, satellite GPS parameters, satellite time information and original remote sensing image data values;

[0063] Step three: according to the data in step two, combined with the remote sensing load design parameters, calculate the ground observation incident angle of the remote sensing image pixel point;

[0064] Step four: according to the incident angle in step three and the positioning precision requirement, calculate the maximum error value D_sub of the elevation;

[0065] Step five: set the elevation of the pixel point as the highest altitude on the earth, recorded as the previous elevation Dem1 of the pixel point, bring it into the direct geometric positioning algorithm to calculate the corresponding longitude and latitude, recorded as Lon1 and Lat1, and find the corresponding elevation information Dem1' of the point in the global ground elevation data, calculate the difference between Dem1 and Dem1', recorded as D_down1, if the difference is less than or equal to 0, then record the actual elevation of the pixel point as Dem1, and the positioning longitude and latitude of the pixel point as Lon1 and Lat1, and end the calculation; if the difference is greater than 0, execute step six.

[0066] Step six: calculate the difference between the previous elevation Dem1 of the pixel point and the maximum error value D_sub of the elevation, recorded as the subsequent elevation Dem2 of the pixel point, and judge whether it is greater than 0. If it is greater than 0, execute step seven, if it is less than or equal to 0, set Dem2 as 0, and execute step eight;

[0067] Step seven: bring the subsequent elevation Dem2 of the pixel point into the direct geometric positioning algorithm to calculate the corresponding longitude and latitude, recorded as Lon2 and Lat2, and find the corresponding elevation information Dem2' of the point in the global ground elevation data, calculate the difference between Dem2 and Dem2', recorded as D_down2, if the difference is less than or equal to 0, execute step eight; if the difference is greater than 0, modify the value of Dem1 to Dem2 and the value of D_down1 to D_down2, and execute step six.

[0068] Step eight: according to the Dem1, Dem1', D_down1 and Dem2, Dem2', D_down2 two groups of parameters calculated in the previous steps, the elevation information of the intersection point is calculated, which is recorded as the actual elevation of the pixel point, and step nine is executed.

[0069] Step nine: the actual elevation of the pixel point is brought into the direct geometric positioning algorithm to calculate the corresponding latitude and longitude, that is, the positioning latitude and longitude of the pixel point.

[0070] In the present application, in order to obtain high-precision latitude and longitude information of satellite remote sensing images in real time on orbit under the limitation of the calculation and storage capacity of the on-board processing system, the precision requirement of on-board geometric positioning is set, and the high-precision global ground elevation data is down-sampled according to the requirement and stored in the on-board processing system.

[0071] Setting the precision requirement of on-board geometric positioning;

[0072] In the present application, the precision requirement of on-board geometric positioning represents the error requirement of the on-board real-time positioning of the remote sensing image by the on-board processing system, which should be set according to the load resolution parameter and the positioning purpose of the remote sensing image, and should be greater than the latitude and longitude precision of the down-sampled high-precision global ground elevation data. The high-precision global ground elevation data is the global elevation data obtained by the radar terrain mapping on the space shuttle, and the precision is about 30m.

[0073] Down-sampling of global ground elevation data

[0074] In the present application, the global ground elevation data grid should be redrawn according to the set precision requirement of on-board geometric positioning, and then the down-sampled elevation grid data is calculated through interpolation operation.

[0075] Receiving satellite position and attitude data and remote sensing image data on orbit

[0076] In the present application, the on-board processing system receives satellite telemetry data and original remote sensing data in real time on orbit through the pre-configured interface, and analyzes and obtains satellite attitude parameters, satellite GPS parameters, satellite time information and original remote sensing image data values.

[0077] Calculating the observation incidence angle of the pixel point to the ground

[0078] In the present application, the calculation method of the observation incidence angle of the pixel point to the ground is to calculate the angle between the visual axis of the pixel point and the vertical vector from the satellite center to the earth center.

[0079] Calculating the maximum error value of the elevation

[0080] In the present application, the calculation method of the maximum error value D_sub of the elevation is

[0081] D_sub = Prec / tanv;

[0082] wherein Prec is the geometric positioning accuracy requirement on satellite, unit m; v is the observation incidence angle of the remote sensing image pixel point, unit rad.

[0083] Direct geometric positioning algorithm

[0084] In the present application, the direct geometric positioning algorithm is to convert the line of sight of the remote sensing image pixel point in the satellite orbit system to the geocentric coordinate system, and then calculate the intersection point of the line of sight in the geocentric coordinate system and the earth ellipsoid model. The longitude and latitude corresponding to the intersection point are the position information of the pixel point.

[0085] Fixed elevation data iterative calculation

[0086] In the present application, the pixel point elevation is set as a fixed value, which is iteratively brought into the direct geometric positioning algorithm for operation, and the purpose is to calculate the range and proportional relationship of the actual elevation of the pixel point. The setting order of the elevation data is from the highest altitude to the sea level, and the high-to-low manner can avoid false elevation in some special terrain conditions, thereby affecting the positioning accuracy of the pixel point.

[0087] Calculation of actual elevation of pixel point

[0088] In the present application, the calculation method of the actual elevation of the pixel point is the principle of similar triangles, and the elevation information of the intersection point is calculated according to the proportional relationship of the lengths of two triangles.

[0089] In the present application, the pixel point elevation is set as a fixed value, and the direct geometric positioning algorithm is iteratively brought into operation from the highest altitude to the sea level in a high-to-low manner, and the purpose is to calculate the range and proportional relationship of the actual elevation of the pixel point, as shown in Figure 2 , it is determined that the actual elevation of the pixel point is between B' and D', and the elevation information of the intersection point is calculated according to the principle of similar triangles. The setting order of the elevation data is in a high-to-low manner, so that false elevation can be avoided in some special terrain conditions, thereby affecting the positioning accuracy of the pixel point. As shown in Figure 3 , if the low-to-high manner is used for calculation, a false elevation point in blue will be calculated, and the true elevation is the position of the red point. Figure 3

[0090] ​The application also provides a satellite remote sensing image on-board geometric positioning system based on ground elevation data, which can be realized by performing the flow steps of the satellite remote sensing image on-board geometric positioning method based on ground elevation data, i.e., the satellite remote sensing image on-board geometric positioning method based on ground elevation data can be understood by those skilled in the art as the preferred embodiment of the satellite remote sensing image on-board geometric positioning system based on ground elevation data.

[0091] Example 2

[0092] Embodiment 2 is a preferred example of embodiment 1

[0093] Referring to Figure 4 For the elevation data of Hainan area, it can be seen that a small part of the area of Hainan has a higher altitude, and the highest is 1800 meters. Using the microwave imager remote sensing data of the Fengyun series satellite, the positioning accuracy difference between the direct geometric positioning algorithm and the algorithm of the application is tested.

[0094] The following gives part of the calculation results of the latitude data of the higher altitude area of Hainan, wherein Lat1 is the calculation result of the direct geometric positioning algorithm, and Lat2 is the result of the satellite remote sensing image on-board geometric positioning method based on ground elevation data of the application. It can be seen from the difference between Lat2 and Lat that in the place with higher altitude, the difference in latitude positioning between the application and the direct geometric positioning algorithm is 0.012966°, and in the place with lower altitude, the difference is 3.2*10 -5 The calculation result shows that the method of the application can improve the accuracy of direct geometric positioning to a certain extent.

[0095]

[0096]

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[0099]

[0100] Those skilled in the art know that, in addition to implementing the system provided by the present application and each device, module and unit thereof in the form of pure computer readable program code, the system provided by the present application and each device, module and unit thereof can also be implemented in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers and embedded microcontrollers, etc. by logically programming the method steps to achieve the same functions. Therefore, the system provided by the present application and each device, module and unit thereof can be considered as a hardware component, and the devices, modules and units included therein for achieving various functions can also be considered as structures within the hardware component; the devices, modules and units for achieving various functions can also be considered as both software modules implementing methods and structures within hardware components.

[0101] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the specific embodiments described above, and various changes or modifications can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application. The embodiments of the present application and the features in the embodiments can be combined with each other in any manner without conflict.

Claims

1. A method for geometric positioning of satellite remote sensing images based on ground elevation data, characterized in that: include: Step S1: setting the accuracy requirement of on-board geometric positioning, downsampling the global ground elevation data according to the set accuracy requirement of on-board geometric positioning, and storing the data in the on-board processing system; Step S2: The onboard processing system receives satellite telemetry data and raw remote sensing data on orbit, and parses and obtains satellite attitude parameters, satellite GPS parameters, satellite time information, and raw remote sensing image data values; Step S3: Calculate the Earth observation angle of the remote sensing image pixel based on the acquired satellite attitude parameters, satellite GPS parameters, satellite time information and original remote sensing image data values, combined with the remote sensing payload design parameters; Step S4: Calculate the maximum error value D_sub of the elevation based on the calculated earth observation incident angle of the remote sensing image pixel point and the positioning accuracy requirement; Step S5: Set the elevation of the remote sensing image pixel point to the highest altitude on Earth, recorded as the pixel point's pre-order elevation Dem1, and calculate the corresponding longitude and latitude, recorded as Lon1 and Lat1. Search the global ground elevation data for the elevation information corresponding to this point, Dem1', and calculate the difference D_down1 between Dem1 and Dem1'. If the difference is less than or equal to 0, record the actual elevation of the pixel point as Dem1, and the pixel point's positioning longitude and latitude as Lon1 and Lat1, and end the calculation. If the difference is greater than 0, trigger the execution of step S6. Step S6: Calculate the difference between the pixel's preceding elevation Dem1 and the maximum elevation error value D_sub, record it as the pixel's subsequent elevation Dem2, and determine whether it is greater than 0; if it is greater than 0, trigger the execution of step S7; if it is less than or equal to 0, set Dem2 to 0, trigger the execution of step S8; Step S7: Calculate the corresponding longitude and latitude based on the pixel point's subsequent elevation Dem2, record them as Lon2 and Lat2, and search for the elevation information Dem2' corresponding to this point in the global ground elevation data. Calculate the difference between Dem2 and Dem2', record them as D_down2. If the difference is less than or equal to 0, trigger the execution of step S8; if the difference is greater than 0, modify the value of Dem1 to Dem2, the value of D_down1 to D_down2, and repeat the triggering of step S6. Step S8: Calculate the elevation information of the intersection point based on the two sets of parameters Dem1, Dem1', D_down1 and Dem2, Dem2', D_down2 obtained by calculation, record it as the actual elevation of the pixel point, and trigger step S9; Step S9: Calculate the corresponding longitude and latitude according to the actual elevation of the pixel point. The corresponding longitude and latitude currently calculated are the longitude and latitude of the pixel point.

2. The on-board geometric positioning method for satellite remote sensing images based on ground elevation data according to claim 1, characterized in that: The accuracy requirements for setting the on-board geometric positioning include: The on-board geometric positioning accuracy requirement refers to the latitude and longitude error requirement of the on-board processing system for real-time on-board positioning of remote sensing images, and should be set based on the payload resolution parameters and the positioning purpose of the remote sensing images. The on-board geometric positioning accuracy should be greater than the latitude and longitude accuracy of the down-sampled high-precision global ground elevation data; The high-precision global ground elevation data is global elevation data obtained from radar topography mapping on a space shuttle.

3. The on-board geometric positioning method for satellite remote sensing images based on ground elevation data according to claim 1, characterized in that: The step S3 adopts: the method for calculating the earth observation incidence angle of the remote sensing image pixel point is to calculate the angle between the satellite pixel point's line of sight vector to the earth and the vertical vector from the satellite center to the earth's center; The satellite pixel point-to-earth line-of-sight vector is calculated based on the acquired satellite attitude parameters, satellite GPS parameters, satellite time information and original remote sensing image data values, combined with remote sensing payload design parameters.

4. The on-board geometric positioning method for satellite remote sensing images based on ground elevation data according to claim 1, characterized in that: The step S4 adopts: D_sub = Prec / tanv; Where Prec is the geometric positioning accuracy requirement on the satellite; v is the incident angle of the remote sensing image pixel point to the earth.

5. The on-board geometric positioning method for satellite remote sensing images based on ground elevation data according to claim 1, characterized in that: The step S5 adopts: the visual axis of the pixel point of the remote sensing image in the satellite orbit system is converted to the geocentric rotating coordinate system through a conversion matrix, and then the intersection of the visual axis in the geocentric rotating coordinate system and the earth ellipsoid model is calculated, and the longitude and latitude corresponding to the intersection position are the position information of the pixel point.

6. A satellite remote sensing image onboard geometric positioning system based on ground elevation data, characterized in that: include: Module M1: Sets the accuracy requirements of on-board geometric positioning, downsamples the global ground elevation data according to the set accuracy requirements of on-board geometric positioning, and stores it in the on-board processing system; Module M2: The onboard processing system receives satellite telemetry data and raw remote sensing data on orbit, and parses and obtains satellite attitude parameters, satellite GPS parameters, satellite time information, and raw remote sensing image data values; Module M3: Calculates the Earth observation angle of the remote sensing image pixel based on the acquired satellite attitude parameters, satellite GPS parameters, satellite time information and original remote sensing image data values, combined with the remote sensing payload design parameters; Module M4: Calculate the maximum error value D_sub of the elevation based on the calculated earth observation incident angle of the remote sensing image pixel point and the positioning accuracy requirement; Module M5: Set the elevation of the remote sensing image pixel point to the highest altitude on Earth, recorded as the pixel point's pre-order elevation Dem1, and calculate the corresponding longitude and latitude, recorded as Lon1 and Lat1. Find the elevation information Dem1' corresponding to this point in the global ground elevation data, and calculate the difference D_down1 between Dem1 and Dem1'; if the difference is less than or equal to 0, then record the actual elevation of the pixel point as Dem1, and the pixel point's positioning longitude and latitude as Lon1 and Lat1, and end the calculation; if the difference is greater than 0, trigger the execution of module M6; Module M6: Calculate the difference between the pixel's previous elevation Dem1 and the maximum elevation error D_sub, record it as the pixel's subsequent elevation Dem2, and determine whether it is greater than 0; if it is greater than 0, trigger the execution of module M7; if it is less than or equal to 0, set Dem2 to 0, and trigger the execution of module M8; Module M7: Calculate the corresponding longitude and latitude based on the pixel point's subsequent elevation Dem2, recorded as Lon2 and Lat2, and search for the elevation information Dem2' corresponding to this point in the global ground elevation data. Calculate the difference between Dem2 and Dem2', recorded as D_down2. If the difference is less than or equal to 0, trigger the execution of module M8; if the difference is greater than 0, modify the value of Dem1 to Dem2 and the value of D_down1 to D_down2, and repeat the triggering of module M6. Module M8: Calculates the elevation information of the intersection point based on the two sets of parameters Dem1, Dem1', D_down1 and Dem2, Dem2', D_down2 obtained, records it as the actual elevation of the pixel point, and triggers module M9; Module M9: Calculate the corresponding longitude and latitude according to the actual elevation of the pixel point. The corresponding longitude and latitude currently calculated are the longitude and latitude of the pixel point.

7. The on-board geometric positioning system for satellite remote sensing images based on ground elevation data according to claim 6, characterized in that: The accuracy requirements for setting the on-board geometric positioning include: The on-board geometric positioning accuracy requirement refers to the latitude and longitude error requirement of the on-board processing system for real-time on-board positioning of remote sensing images, and should be set based on the payload resolution parameters and the positioning purpose of the remote sensing images. The on-board geometric positioning accuracy should be greater than the latitude and longitude accuracy of the down-sampled high-precision global ground elevation data; The high-precision global ground elevation data is global elevation data obtained from radar topography mapping on a space shuttle.

8. The on-board geometric positioning system for satellite remote sensing images based on ground elevation data according to claim 6, characterized in that: The module M3 adopts: the calculation method of the incident angle of the remote sensing image pixel point to the earth is to calculate the angle between the satellite pixel point's line of sight vector to the earth and the vertical vector from the satellite center to the earth's center; The satellite pixel point-to-earth line-of-sight vector is calculated based on the acquired satellite attitude parameters, satellite GPS parameters, satellite time information and original remote sensing image data values, combined with remote sensing payload design parameters.

9. The on-board geometric positioning system for satellite remote sensing images based on ground elevation data according to claim 6, characterized in that: The module M4 adopts: D_sub = Prec / tanv; Where Prec is the geometric positioning accuracy requirement on the satellite; v is the incident angle of the remote sensing image pixel point to the earth.

10. The on-board geometric positioning system for satellite remote sensing images based on ground elevation data according to claim 6, characterized in that: The module M5 adopts the following method: the visual axis of the remote sensing image pixel point in the satellite orbit system is converted to the geocentric rotating coordinate system through a conversion matrix, and then the intersection of the visual axis in the geocentric rotating coordinate system and the earth ellipsoid model is calculated. The longitude and latitude corresponding to the intersection position are the position information of the pixel point.

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