A SAR geocoding method and system considering geometric distortion identification

Abstract

The application provides a SAR geocoding method and system considering geometric distortion identification, comprising: obtaining original SAR image data and DSM data of a target area to obtain preprocessed image data, and generating an equal-Doppler approximate profile; according to SAR imaging geometry and an incident angle parameter, traversing the equal-Doppler approximate profile to identify a shadow area; according to the coordinates of an end point in the equal-Doppler approximate profile and the incident angle, fitting a distance line tangent equation corresponding to any pixel in the profile through a first-order equation; using the distance line tangent equation to detect intersection points, and combining the shadow area to filter the intersection points to obtain two-dimensional profile coordinates corresponding to the pixel; performing distance error compensation and height error compensation on the two-dimensional profile coordinates to obtain compensated two-dimensional profile coordinates; performing coordinate conversion on the two-dimensional profile coordinates to obtain geocoding of a current distance interval, and traversing all distance intervals and all image rows until geocoding of all pixels is completed.

Description

Technical Field

[0001] This invention relates to the field of remote sensing imaging technology, and in particular to a SAR geocoding method and system that takes into account geometric distortion identification. Background Technology

[0002] Spaceborne Synthetic Aperture Radar (SAR), as an active imaging remote sensing Earth observation technology, has the characteristics of all-day, all-weather, and non-contact operation. Based on this, the Interferometric SAR (InSAR) technology developed by SAR can use the phase difference between double-track images to deduce the millimeter-level displacement of ground objects, which can provide continuous, accurate, and large-scale deformation monitoring for urban areas and ensure the safe operation of cities.

[0003] SAR geocoding refers to the process of transforming SAR imagery from a two-dimensional radar coordinate system (slant range-Doppler) to a three-dimensional geodetic coordinate system (longitude, latitude, and elevation). By reconstructing the physical location of SAR pixels, it achieves an accurate correspondence between radar signals and ground features. In InSAR deformation monitoring in urban scenarios, high-precision geocoding results are extremely crucial. They provide the foundation for associating abnormal deformation with specific infrastructure, and can effectively support the rapid tracing of potential hazards and the in-depth interpretation of deformation mechanisms.

[0004] There are two main general technical approaches to SAR geocoding. One approach uses a two-dimensional lookup table based on imaging geometry, such as the Range-Doppler (RD) equation. External elevation data, such as a Digital Elevation Model (DEM) or Digital Surface Model (DSM), is back-projected grid-by-grid to radar coordinates, generating a lookup table from geographic coordinates to radar coordinates. The elevation of each SAR pixel is then obtained through resampling / interpolation, and the geodetic coordinates of each pixel are iteratively calculated using the forward RD equation. This method has wide applicability, but suffers from high computation and resampling overhead, and resampling can easily lead to a loss of geometric and elevation accuracy.

[0005] Another approach is the Rational Function Model (RFM), which approximates the sensor-to-ground geometry using rational polynomials and achieves geocoding through coefficient fitting. Its advantages include simplicity, high efficiency, and platform independence. However, it suffers from limited adaptability to the strong nonlinearity of SAR side-look geometry and terrain undulations, and reliance on sufficient and uniformly distributed control points or rigorous model-generated samples.

[0006] Due to the side-looking imaging mechanism of SAR, two types of geometric distortions are prone to occur in undulating terrain or densely populated urban scenes: overlay and shadow. Both have a significant impact on geocoding results. Overlay occurs when echoes from higher locations (such as building tops or ridges) arrive before those from lower locations (such as the ground or building bases). This causes multiple scatterers at different heights and orientations to be "compressed" into the same slant range pixel, resulting in an inverted order of ground features. Consequently, the relationship between radar imagery and 3D geodetic coordinates becomes one-to-many. In traditional geocoding, pixels and ground features are often considered to have a one-to-one correspondence, and overlay pixels are only located at a single position, resulting in missing target information. Shadows, on the other hand, are areas obscured by tall objects in front and not illuminated by radar. These areas have almost no effective echoes, and conventional geocoding methods cannot identify shadowed areas, thus assigning theoretical geodetic coordinates to pixels in shadowed areas, interfering with the interpretation of the true results.

[0007] In summary, existing geocoding methods face two key shortcomings: first, the computation speed is limited due to intensive iterative calculations; second, they cannot handle geometric distortions, resulting in decreased positioning accuracy in complex terrain areas such as urban scenarios. Summary of the Invention

[0008] This invention provides a SAR geocoding method and system that takes into account geometric distortion identification, in order to solve the defects of slow calculation speed and inability to identify and restore geometric distortion in the current SAR image geocoding technology, and achieve high-precision SAR geocoding.

[0009] In a first aspect, the present invention provides a SAR geocoding that takes into account geometric distortion identification, comprising: Acquire raw SAR image data and DSM data of the target area, perform data preprocessing, and obtain preprocessed image data; Based on the preprocessed image data, an approximate Doppler profile is generated; Based on SAR imaging geometry and incident angle parameters, the shadowed regions are identified by traversing the equivalent Doppler approximation profile. Based on the coordinates of the endpoints and the incident angle in the Doppler approximation profile, the equation of the equidistant tangent line corresponding to any pixel in the profile is obtained by fitting a linear equation. Intersection point detection is performed using the tangent equation of the equidistant line, and intersection point filtering is performed in combination with the shadow area to obtain the two-dimensional profile coordinates corresponding to the pixel; The two-dimensional profile coordinates are compensated for distance and elevation errors to obtain the compensated two-dimensional profile coordinates. The coordinates of the two-dimensional profile are transformed to obtain the geocoding of the current distance interval. All distance intervals and all image rows are traversed until the geocoding of all pixels is completed.

[0010] According to the SAR geocoding method considering geometric distortion identification provided by the present invention, the original SAR image data and DSM data of the target area are acquired, and data preprocessing is performed to obtain preprocessed image data, including: The DSM data is oversampled so that the resolution of the DSM data is a preset multiple of the original SAR image data; Obtain the parameter file of the original SAR image data, and calculate the geodetic coordinates of the four corner points in the original SAR image data using the RD equation based on the elevation range of the DSM data. The polygon obtained by connecting four geodetic coordinates is used as the image coverage area. Based on the image coverage area, it is expanded along the southeast, northwest and other directions to obtain the image buffer coverage area. Based on the image buffer coverage area, the DSM data is cropped so that the coverage area of ​​the DSM data is consistent with the coverage area of ​​the image buffer.

[0011] According to the present invention, a SAR geocoding method considering geometric distortion identification generates an iso-Doppler approximate profile based on the preprocessed image data, comprising: In any row of the preprocessed image data, a DSM profile is generated according to the determined profile line step size parameters; Take the first and last endpoints within any interval in the distance direction of the DSM profile, and calculate the latitude and longitude of the first and last endpoints based on the elevation range of the DSM using the RD equation; Connect the two endpoints on the DSM and project them onto the ground to obtain the profile line. Obtain discrete elevation points according to the preset sampling interval, connect all discrete elevation points to generate a two-dimensional profile, which serves as the spatial candidate solution set for pixels within the distance interval. Using the two-dimensional profile as a two-dimensional coordinate system, where the x-axis is the distance from the ground to the starting point and the y-axis is the elevation corresponding to the distance, the transformation relationship between the coordinates of any point in the two-dimensional coordinate system and the corresponding three-dimensional geodetic coordinates is obtained based on the geodetic azimuth.

[0012] According to the present invention, a SAR geocoding method considering geometric distortion identification identifies shadow regions by traversing the iso-Doppler approximate profile based on SAR imaging geometry and incident angle parameters, including: Determine the variation characteristics of the local incident angle with monotonically increasing ground distance within the radar visible area; Based on the aforementioned change characteristics, connect any two discrete points within the profile, calculate the slope between the two points, and determine whether any point is a visible point. If the slope is determined to be greater than the local incident angle slope, then any point is marked as a visible point, the slope of the next adjacent point of any point is calculated, and the visibility of the adjacent points is determined. If the slope is less than the local incident angle slope, then mark any point as a shaded point, calculate the next neighboring point of any other point, and determine the visibility of the neighboring points. Repeat the sampling calculation until all profile lines are traversed to obtain the shaded area.

[0013] According to the SAR geocoding method considering geometric distortion identification provided by the present invention, the equation of the tangent line corresponding to any pixel in the profile is obtained by fitting a linear equation based on the coordinates of the endpoints and the incident angle in the iso-Doppler approximate profile, including: Obtain the coordinates of the first endpoint and the incident angle of the first endpoint within the same Doppler approximation profile, and obtain the electromagnetic wave tangent equation corresponding to the starting pixel based on the coordinates of the first endpoint and the incident angle of the first endpoint. Determine the adjacent pixel interval, and based on the adjacent pixel interval and the electromagnetic wave tangent equation corresponding to the starting pixel, obtain the electromagnetic wave tangent equation corresponding to any pixel.

[0014] According to the SAR geocoding method considering geometric distortion identification provided by the present invention, the intersection point detection is performed using the tangent equation of the equidistant line, and the intersection point filtering is performed in combination with the shadow area to obtain the two-dimensional profile coordinates corresponding to the pixel, including: As the tangent moves along the distance, calculate the difference between the elevation value of each sampling point on the tangent equation and the true elevation value of each sampling point; If the sign of the difference changes, an intersection point is determined and used as the solution for the corresponding pixel in three-dimensional space; If the tangent and the profile produce multiple intersection points, then the corresponding pixel is determined to be a superimposed pixel; Intersections within the shadow area are filtered out, and any intersection where the x-axis distance between any two intersections is less than a preset ratio of pixel spacing is also filtered out.

[0015] According to the SAR geocoding method for considering geometric distortion identification provided by the present invention, the two-dimensional profile coordinates are subjected to range error compensation and elevation error compensation to obtain the compensated two-dimensional profile coordinates, including: Based on the Earth's radius corresponding to the image area, the distance from the satellite to the Earth's center, and the spacing between adjacent pixels, update the electromagnetic wave tangent equation corresponding to any pixel to perform range error compensation; The difference in incident angles between adjacent pixels is calculated using the spacing between adjacent pixels, the distance from the satellite to the image area, the Earth's radius corresponding to the image area, and the incident angle of the current pixel. The geocentric angle corresponding to the starting point of the coordinate axis is calculated from the Earth's radius corresponding to the image area, the distance from the satellite to the Earth's center, and the distance from the satellite to the image area. The distance from the current positioning result to the satellite is calculated from the current elevation, the distance from the satellite to the Earth's center, the Earth's radius corresponding to the image area, and the geocentric angle corresponding to the starting point of the coordinate axis. Elevation compensation is calculated from the distance from the satellite to the image area, the distance from the current positioning result to the satellite, and the incident angle of the current pixel.

[0016] Secondly, the present invention also provides a SAR geocoding system that takes into account geometric distortion identification, comprising: The preprocessing module is used to acquire the raw SAR image data and DSM data of the target area, perform data preprocessing, and obtain preprocessed image data. The generation module is used to generate an equal Doppler approximate profile based on the preprocessed image data; The identification module is used to identify shadowed regions by traversing the same Doppler approximate profile based on SAR imaging geometry and incident angle parameters. The fitting module is used to obtain the equation of the equidistant tangent line corresponding to any pixel in the profile by fitting a linear equation based on the coordinates of the endpoints and the incident angle in the Doppler approximation profile. The filtering module is used to detect intersections using the equation of the tangent of the equidistant line and to filter the intersections in combination with the shadow area to obtain the two-dimensional profile coordinates corresponding to the pixel. The compensation module is used to perform distance error compensation and elevation error compensation on the two-dimensional profile coordinates to obtain the compensated two-dimensional profile coordinates. The transformation module is used to perform coordinate transformation on the two-dimensional profile coordinates to obtain the geocoding of the current distance interval, and traverse all distance intervals and all image rows until the geocoding of all pixels is completed.

[0017] Thirdly, the present invention also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the SAR geocoding method for taking into account geometric distortion identification as described above.

[0018] Fourthly, the present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the SAR geocoding method taking into account geometric distortion identification as described above.

[0019] The SAR geocoding method and system provided by this invention, which takes into account geometric distortion identification, simplifies SAR pixel localization from iteratively solving three equations to two-dimensional spatial intersection detection by using an approximate equal Doppler surface. This significantly shortens the geocoding runtime, effectively detects overlapping areas in SAR images, eliminates geometric distortions caused by overlapping, correctly restores the vertical structure of ground objects, effectively identifies shadowed areas in images, assists in image interpretation, and avoids the resampling process of traditional methods, achieving higher-precision geocoding. Attached Figure Description To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is one of the flowcharts of the SAR geocoding method that takes into account geometric distortion identification provided by the present invention; Figure 2 This is a schematic diagram illustrating the principle of SAR geocoding that takes into account geometric distortion identification by constructing an approximate equal Doppler surface, as provided by the present invention. Figure 3 This is the second flowchart of the SAR geocoding method that takes into account geometric distortion identification provided by the present invention; Figure 4 This is a schematic diagram of shadow detection based on an approximate iso-Doppler surface provided by the present invention; Figure 5 This is a schematic diagram illustrating the principle of dynamically adjusting the tangent equation and detecting the intersection point provided by the present invention; Figure 6 This is a schematic diagram of the error compensation principle provided by the present invention, wherein... Figure 6 In this context, 'a' represents distance-related error compensation. Figure 6 In this context, 'b' represents elevation-related error compensation. Figure 7 This is a geocoding result map obtained by processing the test SAR image provided by this invention through the process of this invention, wherein... Figure 7 In the image, 'a' represents the TerraSAR-X strip image of the experimental area. Figure 7 In this context, 'b' represents a top view of the encoding result. Figure 7 In this context, 'c' represents the side view of the encoded result. Figure 7 In the image, 'd' represents a magnified view of a portion of the encoding result. Figure 8 This is a schematic diagram of the SAR geocoding system that takes into account geometric distortion identification provided by the present invention; Figure 9This is a schematic diagram of the structure of the electronic device provided by the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0022] Figure 1 This is one of the flowcharts illustrating the SAR geocoding method that takes into account geometric distortion identification provided in this embodiment of the invention, such as... Figure 1 As shown, it includes: Step 100: Acquire the raw SAR image data and DSM data of the target area, perform data preprocessing, and obtain preprocessed image data; Step 200: Based on the preprocessed image data, generate an approximate Doppler profile; Step 300: Based on the SAR imaging geometry and incident angle parameters, traverse the equal Doppler approximate profile to identify the shadow region; Step 400: Based on the coordinates of the endpoints and the incident angle in the Doppler approximation profile, obtain the equation of the equidistant tangent line corresponding to any pixel in the profile by fitting a linear equation; Step 500: Use the equidistant line tangent equation to detect intersection points, and combine the shadow area to filter intersection points to obtain the two-dimensional profile coordinates corresponding to the pixel; Step 600: Perform distance error compensation and elevation error compensation on the two-dimensional profile coordinates to obtain the compensated two-dimensional profile coordinates; Step 700: Perform coordinate transformation on the two-dimensional profile coordinates to obtain the geocoding of the current distance interval, traverse all distance intervals and all image rows until the geocoding of all pixels is completed.

[0023] Figure 2 A schematic diagram of the principle of an embodiment of the present invention is given, as follows: Figure 2As shown, this invention, based on SAR oblique-view imaging geometry, approximates the iso-Doppler surface at the imaging time, transforming the solution for candidate points in three-dimensional space into an intersection detection problem in a two-dimensional plane. The RD equation is used to calculate the straight-line range of pixels in a specified interval on the DSM (Distributed Segment Map), extracting the corresponding DSM profile. Combined with the satellite's incident angle, the shadowed areas of the image within this profile range can be detected, and the tangent equation for the incident electromagnetic wave can be constructed. Calculating the intersection of the tangent equation and the DSM profile line allows for the identification of overlay points and the determination of their geographic coordinates. Accuracy compensation for distance and elevation is performed at the end, ultimately outputting the geographic result after restoring geometric distortion. By simplifying the complex iterative calculations in traditional geocoding methods, this invention achieves a faster coding speed.

[0024] Specifically, the embodiments of the present invention include the following steps: raw data acquisition, DSM data cropping, approximate equal Doppler profile generation, shadow region identification, tangent equation generation, intersection detection, error compensation, and result output.

[0025] Figure 3 A flowchart of a SAR geocoding method for urban scenes that takes geometric distortion recognition into account, according to an embodiment of the present invention, is provided, specifically including: Step S11: Acquire the original image and high-resolution DSM of the target area, and perform data preprocessing. This is divided into three sub-steps: S111, S112, and S113.

[0026] S111: Oversample the DSM to a resolution much higher than that of the SAR image, ensuring the accuracy of elevation during subsequent positioning. The resolution of the sampled DSM is generally more than three times that of the SAR image.

[0027] S112: Read the parameter file of the original image, calculate the geodetic coordinates of the four corner points of the image using the RD equation based on the elevation range of the DSM, and use the polygon obtained by connecting the coordinates of the four points as the image coverage area. Based on this area, further expand along the southeast, northwest and south directions, leaving sufficient buffer to ensure the smooth progress of subsequent shadow detection.

[0028] S113: Based on S112, crop the original DSM to ensure that its range is consistent with the original image.

[0029] Step S21: Profile Generation. In any row of the image, generate a DSM profile according to the set profile line step size parameters. Further, select the first and last endpoints within a certain distance interval upwards. and Elevation range based on DSM The corresponding latitude and longitude are calculated using the RD equation. and Connecting the two endpoints on the DSM and projecting them onto the ground yields a profile line. Since the elevations of the corresponding grid cells on the profile line are known, discrete elevation points can be obtained according to the set sampling interval. Connecting these points generates a two-dimensional profile, which serves as the spatial candidate solution set for pixels within that distance interval. This profile can be viewed as a two-dimensional coordinate system, where the x-axis represents the distance from the ground to the starting endpoint, and the y-axis represents the elevation corresponding to that distance. Any point within the coordinate system... Its corresponding three-dimensional geodetic coordinates The conversion relationship is as follows:

[0030] in It is the major azimuth angle between the two endpoints. It is important to note that the endpoints... The corresponding two-dimensional plane coordinates are .

[0031] Step S22: Shadow region identification. Further, as... Figure 4 As shown, shadow identification is performed by traversing the profile curve along the x-axis based on the local incident angle variation trend. Within the radar visible area, the local incident angle... The distance to the ground increases monotonically; once entering the shaded area, When it drops and returns to the visible area, We return to the values ​​taken before the point enters the shadow. Based on this property, we can connect any two discrete points within the profile and calculate the slope between them to determine whether the point is visible. For the first sampling point within the profile, we assume it is a visible point and mark it as... Its adjacent sampling points are The slopes of the two It can be calculated as:

[0032] When the slope is greater than the slope of the incident angle At that time, Mark the point as visible and calculate its slope relative to the next adjacent sampling point to determine visibility; if the slope of both is less than the slope of the incident angle, then... Mark the points as shaded and calculate. Using the slope of the next sampling point, repeat this step until the entire profile line has been traversed. For robust convergence, a buffer of approximately 200 pixels can be added in the negative ground distance direction to determine the reliability of the first visible point; if an intensity map is available, brightness can be used to assist in confirming the first visible point. Identified shadow areas will be directly removed during subsequent intersection point filtering. Step S23: Generating the tangent equation. Specifically, the coordinates of the first point within the profile are known to be... The corresponding angle of incidence is Then the tangent equation of the electromagnetic wave corresponding to the initial pixel can be expressed as:

[0033] When solving for the spatial positions of the remaining pixels along the ground distance, only the intercept needs to be adjusted to obtain the corresponding tangent equation. Assuming the interval between adjacent pixels is r, the tangent equation for the nth pixel on this profile line is:

[0034] Step S24: Intersection detection. For example... Figure 5 As shown, further, as the tangent line moves along the distance direction, the difference between the elevation value of each sampling point on the tangent line equation and its true elevation value is calculated. When two adjacent differences change sign, it indicates that an intersection point has occurred. The x-axis coordinate corresponding to the intersection point can be expressed as:

[0035] in represent Each intersection point represents a solution for the corresponding pixel in 3D space. When a tangent and a profile produce multiple intersection points, the pixel can be identified as a superimposed pixel. It's important to note that intersection points located in shaded areas are invalid and must be filtered out. Furthermore, if the x-axis distance between two intersection points is too small, less than half the pixel interval, it indicates that the two intersection points are in the same resolution unit, and one of them must be filtered out.

[0036] Step S25: Error Correction. Because this geocoding algorithm uses many approximations in the actual calculation process, it has a significant impact on the positioning results, and it is necessary to compensate for the errors caused by these approximations. For example... Figure 6 As shown in 'a', further compensation is made for distance-related errors. Based on geometric relationships, the equation of the nth tangent line on a profile line should be modified as follows:

[0037]

[0038]

[0039] in It is the Earth's radius corresponding to the image area. H represents the distance from the satellite to the image area, and H represents the distance from the satellite to the Earth's center. This indicates the interval between adjacent pixels. Indicates the angle of incidence corresponding to the starting point of the coordinate axis. Indicates the difference in incident angle between adjacent pixels. Indicates the angle of incidence of the current pixel, This represents the geocentric angle corresponding to the starting point of the coordinate axis.

[0040]

[0041]

[0042] Furthermore, such as Figure 6 As shown in b, after the intersection point detection is completed, an elevation compensation needs to be performed based on the calculated elevation, with a corresponding value of...

[0043]

[0044] in, Indicates elevation compensation, This indicates the distance from the current positioning result to the satellite. This indicates the elevation of the current positioning result.

[0045] Step S26: After encoding each row of the image, the two-dimensional coordinates of each intersection point are transformed to obtain the three-dimensional geodetic coordinates of each pixel. At the same time, the overlay area distribution and shadow area distribution of the image are also obtained.

[0046] The following is a specific embodiment of the present invention in an experimental area. The embodiment uses TerraSAR-X strip mode imagery and DSM data is acquired by lidar. The image data resolution is 3m and the DSM data resolution is 1m.

[0047] After implementing the process of this invention, the result is as follows: Figure 7 As shown, a is the TerraSAR-X strip pattern image of the experimental area, and b, c, and d are the front view, side view, and local magnified view of the geocoded result, respectively. From Figure 7 The distribution of shadowed areas and the three-dimensional structure of the experimental area are clearly visible in the magnified image. As can be seen from the enlarged image, this invention successfully overcomes the severe overlay effect of high-rise buildings and successfully recovers their three-dimensional structure, providing a solid foundation for subsequent SAR image interpretation and deformation monitoring. Furthermore, comparisons show that the actual computation speed of this invention is more than five times faster than traditional lookup table-based geocoding methods. The algorithm test was conducted on a personal laptop running a Windows operating system with an i7-12600K CPU and an RTX 4060 graphics card.

[0048] The SAR geocoding system that takes geometric distortion identification into account provided by the present invention is described below. The SAR geocoding system that takes geometric distortion identification into account described below can be referred to in correspondence with the SAR geocoding method that takes geometric distortion identification into account described above.

[0049] Figure 8This is a schematic diagram of the SAR geocoding system that takes into account geometric distortion identification provided by the present invention, as shown below. Figure 8 As shown, it includes: a preprocessing module 81, a generation module 82, a recognition module 83, a fitting module 84, a filtering module 85, a compensation module 86, and a conversion module 87, wherein: The preprocessing module 81 acquires the original SAR image data and DSM data of the target area, performs data preprocessing, and obtains preprocessed image data. The generation module 82 generates an iso-Doppler approximate profile based on the preprocessed image data. The identification module 83 traverses the iso-Doppler approximate profile according to SAR imaging geometry and incident angle parameters to identify shadow areas. The fitting module 84 obtains the equidistant line tangent equation corresponding to any pixel in the profile by fitting a linear equation based on the coordinates of the endpoints and the incident angle in the iso-Doppler approximate profile. The filtering module 85 uses the equidistant line tangent equation to perform intersection detection and combines it with the shadow areas to perform intersection filtering, obtaining the two-dimensional profile coordinates corresponding to the pixel. The compensation module 86 performs range error compensation and elevation error compensation on the two-dimensional profile coordinates to obtain the compensated two-dimensional profile coordinates. The conversion module 87 performs coordinate conversion on the two-dimensional profile coordinates to obtain the geocoding of the current range interval, traversing all range intervals and all image rows until the geocoding of all pixels is completed.

[0050] Figure 9 An example is a schematic diagram of the physical structure of an electronic device, such as... Figure 9As shown, the electronic device may include: a processor 910, a communication interface 920, a memory 930, and a communication bus 940, wherein the processor 910, the communication interface 920, and the memory 930 communicate with each other through the communication bus 940. The processor 910 can call logic instructions in the memory 930 to execute a SAR geocoding method that takes into account geometric distortion identification. This method includes: acquiring raw SAR image data and DSM data of the target area; performing data preprocessing to obtain preprocessed image data; generating an iso-Doppler approximate profile based on the preprocessed image data; traversing the iso-Doppler approximate profile according to SAR imaging geometry and incident angle parameters to identify shadowed areas; obtaining the equidistant line tangent equation corresponding to any pixel in the profile by fitting a linear equation based on the coordinates of the endpoints and the incident angle in the iso-Doppler approximate profile; performing intersection detection using the equidistant line tangent equation and combining it with the shadowed areas for intersection filtering to obtain the two-dimensional profile coordinates corresponding to the pixel; performing range error compensation and elevation error compensation on the two-dimensional profile coordinates to obtain compensated two-dimensional profile coordinates; performing coordinate transformation on the two-dimensional profile coordinates to obtain the geocoding of the current range interval; traversing all range intervals and all image rows until the geocoding of all pixels is completed.

[0051] Furthermore, the logical instructions in the aforementioned memory 930 can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0052] On the other hand, the present invention also provides a non-transitory computer-readable storage medium storing a computer program thereon. When executed by a processor, the computer program implements a SAR geocoding method for considering geometric distortion identification provided by the methods described above. The method includes: acquiring raw SAR image data and DSM data of a target area, performing data preprocessing to obtain preprocessed image data; generating an iso-Doppler approximate profile based on the preprocessed image data; traversing the iso-Doppler approximate profile according to SAR imaging geometry and incident angle parameters to identify shadow areas; obtaining the equidistant line tangent equation corresponding to any pixel in the profile by fitting a linear equation based on the coordinates of the endpoints and the incident angle in the iso-Doppler approximate profile; performing intersection detection using the equidistant line tangent equation and combining it with the shadow areas for intersection filtering to obtain two-dimensional profile coordinates corresponding to the pixel; performing range error compensation and elevation error compensation on the two-dimensional profile coordinates to obtain compensated two-dimensional profile coordinates; performing coordinate transformation on the two-dimensional profile coordinates to obtain the geocoding of the current range interval, traversing all range intervals and all image rows until the geocoding of all pixels is completed.

[0053] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0054] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A SAR geocoding method that takes into account geometric distortion identification, characterized in that, include: Acquire raw SAR image data and DSM data of the target area, perform data preprocessing, and obtain preprocessed image data; Based on the preprocessed image data, an approximate Doppler profile is generated; Based on SAR imaging geometry and incident angle parameters, the shadowed regions are identified by traversing the equivalent Doppler approximation profile. Based on the coordinates of the endpoints and the incident angle in the Doppler approximation profile, the equation of the equidistant tangent line corresponding to any pixel in the profile is obtained by fitting a linear equation. Intersection point detection is performed using the tangent equation of the equidistant line, and intersection point filtering is performed in combination with the shadow area to obtain the two-dimensional profile coordinates corresponding to the pixel; The two-dimensional profile coordinates are compensated for distance and elevation errors to obtain the compensated two-dimensional profile coordinates. The coordinates of the two-dimensional profile are transformed to obtain the geocoding of the current distance interval. All distance intervals and all image rows are traversed until the geocoding of all pixels is completed.

2. The SAR geocoding method considering geometric distortion identification according to claim 1, characterized in that, Acquire raw SAR and DSM data of the target area, perform data preprocessing to obtain preprocessed image data, including: The DSM data is oversampled so that the resolution of the DSM data is a preset multiple of the original SAR image data; Obtain the parameter file of the original SAR image data, and calculate the geodetic coordinates of the four corner points in the original SAR image data using the RD equation based on the elevation range of the DSM data. The polygon obtained by connecting four geodetic coordinates is used as the image coverage area. Based on the image coverage area, it is expanded along the southeast, northwest and other directions to obtain the image buffer coverage area. Based on the image buffer coverage area, the DSM data is cropped so that the coverage area of ​​the DSM data is consistent with the coverage area of ​​the image buffer.

3. The SAR geocoding method considering geometric distortion identification according to claim 1, characterized in that, Based on the preprocessed image data, an approximate iso-Doppler profile is generated, including: In any row of the preprocessed image data, a DSM profile is generated based on the determined profile line step size parameters; Take the first and last endpoints within any interval in the distance direction of the DSM profile, and calculate the latitude and longitude of the first and last endpoints based on the elevation range of the DSM using the RD equation; Connect the two endpoints on the DSM and project them onto the ground to obtain the profile line. Obtain discrete elevation points according to the preset sampling interval, connect all discrete elevation points to generate a two-dimensional profile, which serves as the spatial candidate solution set for pixels within the distance interval. Using the two-dimensional profile as a two-dimensional coordinate system, where the x-axis is the distance from the ground to the starting point and the y-axis is the elevation corresponding to the distance, the transformation relationship between the coordinates of any point in the two-dimensional coordinate system and the corresponding three-dimensional geodetic coordinates is obtained based on the geodetic azimuth.

4. The SAR geocoding method considering geometric distortion identification according to claim 1, characterized in that, Based on SAR imaging geometry and incident angle parameters, the shadowed regions are identified by traversing the approximate Doppler profile, including: Determine the variation characteristics of the local incident angle with ground distance monotonically increasing within the radar visible area; Based on the aforementioned change characteristics, connect any two discrete points within the profile, calculate the slope between the two points, and determine whether any point is a visible point. If the slope is determined to be greater than the local incident angle slope, then any point is marked as a visible point, the slope of the next adjacent point of any point is calculated, and the visibility of the adjacent points is determined. If the slope is less than the local incident angle slope, then mark any point as a shaded point, calculate the next neighboring point of any other point, and determine the visibility of the neighboring points. Repeat the sampling calculation until all profile lines are traversed to obtain the shaded area.

5. The SAR geocoding method considering geometric distortion identification according to claim 1, characterized in that, Based on the coordinates of the endpoints and the incident angle in the approximate Doppler profile, the equation of the tangent line corresponding to any pixel in the profile is obtained by fitting a linear equation, including: Obtain the coordinates of the first endpoint and the incident angle of the first endpoint within the same Doppler approximation profile, and obtain the electromagnetic wave tangent equation corresponding to the starting pixel based on the coordinates of the first endpoint and the incident angle of the first endpoint. Determine the adjacent pixel interval, and based on the adjacent pixel interval and the electromagnetic wave tangent equation corresponding to the starting pixel, obtain the electromagnetic wave tangent equation corresponding to any pixel.

6. The SAR geocoding method considering geometric distortion identification according to claim 1, characterized in that, Intersection point detection is performed using the equidistant line tangent equation, and intersection point filtering is performed using the shaded area to obtain the two-dimensional profile coordinates corresponding to the pixel, including: As the tangent moves along the distance, calculate the difference between the elevation value of each sampling point on the tangent equation and the true elevation value of each sampling point; If the sign of the difference changes, an intersection point is determined and used as the solution for the corresponding pixel in three-dimensional space; If the tangent and the profile produce multiple intersection points, then the corresponding pixel is determined to be a superimposed pixel; Intersections within the shadow area are filtered out, and any intersection where the x-axis distance between any two intersections is less than a preset ratio of pixel spacing is also filtered out.

7. The SAR geocoding method considering geometric distortion identification according to claim 1, characterized in that, The two-dimensional profile coordinates are compensated for distance and elevation errors to obtain the compensated two-dimensional profile coordinates, including: Based on the Earth's radius corresponding to the image area, the distance from the satellite to the Earth's center, and the spacing between adjacent pixels, update the electromagnetic wave tangent equation corresponding to any pixel to perform range error compensation; The difference in incident angles between adjacent pixels is calculated using the spacing between adjacent pixels, the distance from the satellite to the image area, the Earth's radius corresponding to the image area, and the incident angle of the current pixel. The geocentric angle corresponding to the starting point of the coordinate axis is calculated from the Earth's radius corresponding to the image area, the distance from the satellite to the Earth's center, and the distance from the satellite to the image area. The distance from the current positioning result to the satellite is calculated from the current elevation, the distance from the satellite to the Earth's center, the Earth's radius corresponding to the image area, and the geocentric angle corresponding to the starting point of the coordinate axis. Elevation compensation is calculated from the distance from the satellite to the image area, the distance from the current positioning result to the satellite, and the incident angle of the current pixel.

8. A SAR geocoding system that takes into account geometric distortion identification, characterized in that, include: The preprocessing module is used to acquire the raw SAR image data and DSM data of the target area, perform data preprocessing, and obtain preprocessed image data. The generation module is used to generate an equal Doppler approximate profile based on the preprocessed image data; The identification module is used to identify shadowed regions by traversing the same Doppler approximate profile based on SAR imaging geometry and incident angle parameters. The fitting module is used to obtain the equation of the equidistant tangent line corresponding to any pixel in the profile by fitting a linear equation based on the coordinates of the endpoints and the incident angle in the Doppler approximation profile. The filtering module is used to detect intersections using the equation of the tangent of the equidistant line and to filter the intersections in combination with the shadow area to obtain the two-dimensional profile coordinates corresponding to the pixel. The compensation module is used to perform distance error compensation and elevation error compensation on the two-dimensional profile coordinates to obtain the compensated two-dimensional profile coordinates. The transformation module is used to perform coordinate transformation on the two-dimensional profile coordinates to obtain the geocoding of the current distance interval, and traverse all distance intervals and all image rows until the geocoding of all pixels is completed.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the SAR geocoding method that takes into account geometric distortion identification as described in any one of claims 1 to 7.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the SAR geocoding method that takes into account geometric distortion identification as described in any one of claims 1 to 7.

Images