Interference SAR image correction method

Abstract

The invention provides an interference SAR image correction method. The method comprises the following steps: obtaining interference SAR data and DTM data; according to the interference SAR data and the DTM data, constructing an initial mapping relation between an SAR slant distance space and a geographic space; acquiring the height of a ground object relative to the ground according to the interference SAR data; correcting the initial plane position coordinate according to the height of the ground object relative to the ground and the interference SAR data to obtain a corrected plane position coordinate; obtaining a ground correction elevation corresponding to the corrected plane position coordinate, correcting the height of the ground object relative to the ground to obtain a ground correction elevation, obtaining the height of the ground object relative to the ground by using interference SAR data, and carrying out plane positioning position correction on the initial plane position coordinate through the height of the ground object relative to the ground to obtain a ground position correction elevation. Errors caused by local geometric distortion are eliminated, and then the corresponding ground elevation is obtained through the corrected plane positioning position.

Description

Technical Field

[0001] The invention relates to the technical field of remote sensing measurement, and in particular to an interferometric SAR image correction method. Background Art

[0002] Synthetic Aperture Radar (SAR) is an advanced active remote sensing measurement device that can quickly and accurately obtain remote sensing data under all-day and all-weather conditions. It is an important data source in remote sensing applications. However, since SAR uses side-view imaging to obtain data, geometric distortion phenomena such as perspective contraction and overlap usually occur in SAR images, which makes it difficult to apply SAR images in subsequent applications.

[0003] The SAR image correction method in the prior art includes: orthorectification assisted by digital elevation model (DEM) data, obtaining the accurate geographical location of each SAR image pixel by solving the RD (Range-Doppler) positioning model, and then sampling the SAR image to the accurate geographical location, thereby achieving the effect of correcting the geometric distortion of the SAR image. However, the DEM data used in the above process generally only contains the elevation information of the terrain, but does not contain or does not accurately contain the height information of the objects such as forests and buildings on the surface relative to the ground, and cannot correct the small-scale local geometric distortion caused by the height of the objects relative to the surface (or DEM).

[0004] In addition, it also includes true radiometric correction with the help of high-precision DSM (Digital Surface Model) data. By solving the true geographical location of the ground object, a specific resampling method is used to correct the local geometric distortion of the ground object. This method is usually applied to building areas. SAR signals cannot penetrate buildings, so the position in the SAR image can be matched with the building elevation position provided by DSM. However, this method is difficult to apply in forest areas because SAR signals have a certain degree of penetration in forest areas. This makes it difficult to accurately know the precise height of the SAR signal in the vertical direction of the forest even with the assistance of high-precision DSM. Therefore, it is impossible to accurately solve the exact geographical location of the forest target and realize the correction of the SAR image of the forest scene. Summary of the invention

[0005] The purpose of the present invention is to provide an interferometric SAR image correction method, which can solve the technical problem that small-scale local geometric distortion caused by the height of the ground object relative to the ground surface cannot be corrected.

[0006] To solve the above problems, the present invention provides an interferometric SAR image correction method, comprising the following steps: Step S1000: Acquire interferometric SAR data and DTM data; Step S2000: constructing an initial mapping relationship between SAR slant range space and geographic space according to the interferometric SAR data and the DTM data; Step S3000: Obtaining the height of the object relative to the ground based on the interferometric SAR data ; Step S4000: According to the height of the ground feature relative to the ground and the initial plane position coordinates of the interferometric SAR data Correction is performed to obtain the corrected plane position coordinates ; Step S5000: According to the corrected plane position coordinates Get the ground corrected elevation corresponding to the coordinate , the height of the object relative to the ground Correction to obtain ground-corrected elevation .

[0007] Furthermore, in the above interferometric SAR image correction method, the initial mapping relationship can be expressed by the following formula: (1) in, and is the coordinate in SAR slant range space, are geographic coordinates, where is the initial plane position coordinate, is the ground elevation.

[0008] Furthermore, in the above interferometric SAR image correction method, the step S4000 further includes: Step S4100: modifying the initial mapping relationship to obtain an accurate mapping relationship.

[0009] Furthermore, in the above-mentioned interferometric SAR image correction method, the precise mapping relationship expression in step S4100 is: (3).

[0010] Furthermore, in the above interferometric SAR image correction method, after step S5000, the following steps are further included: Step S6000: Determine the image range of the geographic space according to the precise mapping relationship, and obtain the coordinates of each pixel of the geographic space. , and calculate the several slant range space pixels closest to the two-dimensional plane distance of the geographic space pixel according to the precise mapping relationship, and count the ground-corrected elevation of the slant range space pixel The quantile height of , according to the quantile height Correct the height of the object of the geographic space pixel to obtain the coordinates of the geographic space pixel .

[0011] Furthermore, in the above interferometric SAR image correction method, after step S5000, the following steps are further included: Step S7000: Determine the image range of the geographic space according to the precise mapping relationship, and obtain the coordinates of each pixel of the geographic space. , and according to the precise mapping relationship, calculate a number of the slant range space pixels that are closest to the three-dimensional distance of the geographic space pixel, and use the inverse distance weighted resampling method to calculate the image value of each of the slant range space pixels as the image value of the geographic space pixel.

[0012] Furthermore, in the above-mentioned interferometric SAR image correction method, the interferometric SAR data is SAR image data in slant range space; and the DTM data is a digital terrain model containing only terrain elevation information.

[0013] Furthermore, in the above-mentioned interferometric SAR image correction method, the step S3000 specifically includes the following steps: Step S3100: performing interference processing on the interferometric SAR data and extracting the interferometric phase information of the interferometric SAR data.

[0014] Step S3200: Remove terrain phase information based on the initial mapping relationship and interferometric SAR data, and extract ground elevation The interference phase information.

[0015] Step S3300: Convert the interferometric phase and height information according to the interferometric SAR imaging geometry to obtain the height of the object relative to the ground. .

[0016] Furthermore, in the above-mentioned interferometric SAR image correction method, the plane position coordinates corrected in step S4000 are The correction value in is calculated as follows: (2) in, For radar perspective, is the angle between the radar side view direction and the due east direction, and are the plane positioning deviations in the east-west and north-south directions, The height of the feature relative to the ground.

[0017] The height of the object relative to the ground is obtained by using the interferometric SAR data, and the height of the object relative to the ground is obtained by using the height of the object relative to the ground. For the initial plane position coordinates The plane positioning position is corrected to eliminate the error caused by local geometric distortion, and then the corresponding ground elevation is obtained through the corrected plane positioning position to complete the correction. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a flowchart of the steps of the embodiment shown in the present invention; Figure 2 Schematic diagram of the remote sensing measurement calculation model of the embodiment of the present invention. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0020] The following is an explanation of an interferometric SAR image correction method shown in the present invention. Figure 1 , specifically including the following steps: Step S1000: Obtain interferometric SAR data and DTM (Digital Terrain Model) data. Specifically, interferometric SAR data is SAR image data in slant range space (R), which needs to meet the ability to measure elevation information, while DTM data is a digital terrain model that only contains terrain elevation information, and does not contain height information of buildings, vegetation, etc. relative to the ground.

[0021] Step S2000: constructing an initial mapping relationship between SAR slant range space (R) and geographic space (M) based on interferometric SAR data and DTM data. The initial mapping relationship can be expressed by the following formula: (1) in, and is the coordinate in SAR slant range space, are geographic coordinates, where are the initial geocoded location coordinates, is the ground elevation.

[0022] Step S3000: Obtaining the height of the object relative to the ground based on the interferometric SAR data , the specific steps are as follows: Step S3100: performing interference processing on the interferometric SAR data and extracting the interferometric phase information of the interferometric SAR data.

[0023] Step S3200: Remove terrain phase information based on the initial mapping relationship and interferometric SAR data, and extract ground elevation The interference phase information.

[0024] Step S3300: Realize ground elevation based on interferometric SAR data The interference phase information and the height of the object relative to the ground The height of the object relative to the ground is obtained by conversion .

[0025] Step S4000: According to the height of the object relative to the ground and the initial plane position coordinates of the interferometric SAR data Correction is performed to obtain the corrected plane position coordinates , the specific correction value calculation formula is as follows: (2) in, For radar perspective, is the angle between the radar side view direction and the due east direction, and are the plane positioning deviations in the east-west and north-south directions, The height of the feature relative to the ground.

[0026] Step S4000 specifically also includes: Step S4100: Then, the initial mapping relationship is corrected to obtain an accurate mapping relationship, and the calculation formula is as follows: (3) Step S5000: Based on the corrected plane position coordinates Get the ground corrected elevation corresponding to the coordinate , the height of the object relative to the ground Correction to obtain ground-corrected elevation , the specific calculation formula is as follows: (4) In order to obtain a more accurate geometric position, step S6000 is further included after step S5000.

[0027] Step S6000: Determine the image range of the geographic space based on the precise mapping relationship and obtain the coordinates of each geographic space pixel , and calculate the two-dimensional plane distance to the geographic space pixel based on the precise mapping relationship (i.e. Figure 2The nearest slant range space pixels (projection distance of the ROF plane) are selected to calculate the ground-corrected elevation of the slant range space pixels. The quantile height of , according to the quantile height Correct the height of the ground object of the geospatial pixel to obtain the coordinates of the geospatial pixel .

[0028] Similarly, in order to obtain a more accurate geometric position, step S7000 is further included after step S6000.

[0029] Step S7000: Determine the image range of the geographic space based on the precise mapping relationship and obtain the coordinates of each geographic space pixel According to the precise mapping relationship, several slant-range spatial pixels with the closest three-dimensional distance to the geographic spatial pixel are calculated, and the SAR intensity, interferometric SAR coherence and other image values ​​of each slant-range spatial pixel are calculated using the inverse distance weighted resampling method as the image value of the geographic spatial pixel.

[0030] Combine the following Figure 2 The working principle of this embodiment is explained. In the figure, ON represents the north direction, OE represents the east direction, OH represents the elevation direction, OF represents the radar flight direction, and OR represents the projection vector of the radar side view direction on the plane; the angle between the center of the radar beam and the vertical direction, that is, the radar viewing angle ; A * Point A corresponds to the top of a tree, and point B corresponds to the SAR signal observation position. Since the SAR signal has a certain degree of penetration, point A is generally lower than point A. * The height of point A relative to point C on the ground is recorded as the ground correction height. , the distances between point A and point B relative to the radar are equal (the slant distances are equal). Therefore, based on the geocoding of the DTM data, the radar will mistakenly identify point A as point B during the measurement process, and correction is required to obtain the true position.

[0031] The three-dimensional coordinates of point B are obtained through the initial mapping relationship between SAR slant range space (R) and geographic space (M). It can be assumed that the three-dimensional coordinates of point B are: , the initial plane position coordinates There is an error. If there is terrain undulation between point B and point C, then there is still an error in the elevation of point A relative to point C. The initial plane position coordinates The error is caused by local geometric distortion, which leads to plane positioning deviation and needs to be corrected in subsequent steps. For the initial plane position coordinates The error caused by local geometric distortion can be eliminated by correction. The height AD of point A relative to point B, that is, the height of the object measured by SAR relative to the ground , the height of the object relative to the ground can be obtained by interfering SAR data , then the plane coordinates of point B can be corrected first, so the coordinates of point A can be corrected to: Then get the height of point C relative to point B, that is, the ground corrected elevation of point C When the interferometric SAR data is used to obtain the height of point C relative to point B, that is, the ground elevation of point C At the same time, since point C is directly below point A, the plane position coordinates of point A can be used to calculate the Get the ground corrected elevation corresponding to the coordinate , that is, the height of point C relative to point D, so the height of point A relative to point C can be calculated (that is, the ground corrected elevation ), and finally the coordinates of point A are corrected to: .

[0032] The trees in the forest area will gradually grow over time, but the DTM data is for the elevation data of the terrain / ground, and it is impossible to update the height data of the trees after growth. The technical solution in this solution can timely update the relative height data of the trees.

[0033] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundaries of the appended claims, or the equivalent forms of such scope and boundaries.

Claims

1. An interferometric SAR image correction method, characterized in that: The steps include: Step S1000: Acquire interferometric SAR data and DTM data; Step S2000: constructing an initial mapping relationship between SAR slant range space and geographic space according to the interferometric SAR data and the DTM data; Step S3000: Obtaining the height of the object relative to the ground based on the interferometric SAR data ; Step S4000: according to the height of the ground feature relative to the ground and the initial plane position coordinates of the interferometric SAR data Correction is performed to obtain the corrected plane position coordinates ; Step S5000: According to the corrected plane position coordinates Get the ground corrected elevation corresponding to the coordinate , the height of the object relative to the ground Correction to obtain ground-corrected elevation .

2. The interferometric SAR image correction method according to claim 1, characterized in that: The initial mapping relationship can be expressed by the following formula: （1） in, and is the coordinate in SAR slant range space, is the geographic space coordinate, where is the initial plane position coordinate, is the ground elevation.

3. The interferometric SAR image correction method according to claim 2, characterized in that: The step S4000 further includes: Step S4100: modifying the initial mapping relationship to obtain an accurate mapping relationship.

4. The interferometric SAR image correction method according to claim 3, characterized in that: The precise mapping relationship expression in step S4100 is: （3）。 5. The interferometric SAR image correction method according to claim 3, characterized in that: After step S5000, the following steps are further included: Step S6000: Determine the image range of the geographic space according to the precise mapping relationship, and obtain the coordinates of each pixel of the geographic space. , and calculate the several slant range space pixels closest to the two-dimensional plane distance of the geographic space pixel according to the precise mapping relationship, and count the ground-corrected elevation of the slant range space pixel Quantile height , according to the quantile height Correct the height of the object of the geographic space pixel to obtain the coordinates of the geographic space pixel .

6. The interferometric SAR image correction method according to claim 5, characterized in that: After step S6000, the following steps are further included: Step S7000: Determine the image range of the geographic space according to the precise mapping relationship, and obtain the coordinates of each pixel of the geographic space. , and according to the precise mapping relationship, calculate a number of the slant range space pixels that are closest to the three-dimensional distance of the geographic space pixel, and use the inverse distance weighted resampling method to calculate the image value of each of the slant range space pixels as the image value of the geographic space pixel.

7. The interferometric SAR image correction method according to claim 1, characterized in that: The interferometric SAR data is SAR image data in slant range space; The DTM data is a digital terrain model that only contains terrain elevation information.

8. The interferometric SAR image correction method according to claim 1, characterized in that: The step S3000 specifically includes the following steps: Step S3100: performing interference processing on the interferometric SAR data and extracting interference phase information of the interferometric SAR data; Step S3200: Remove terrain phase information based on the initial mapping relationship and interferometric SAR data, and extract ground elevation The interference phase information of Step S3300: Convert the interferometric phase and height information according to the interferometric SAR imaging geometry to obtain the height of the object relative to the ground. .

9. The interferometric SAR image correction method according to claim 1, characterized in that: The plane position coordinates corrected in step S4000 The correction value in is calculated as follows: （2） in, For radar perspective, is the angle between the radar side view direction and the due east direction, and are the plane positioning deviations in the east-west and north-south directions, The height of the feature relative to the ground.

Images