Interferometric SAR Image Calibration Method

Abstract

The present invention provides an interferometric SAR image correction method, which includes the following steps: acquiring interferometric SAR data and DTM data; constructing an initial mapping relationship between the SAR slant range space and the geospatial space according to the interferometric SAR data and the DTM data; obtaining the height of a ground object relative to the ground based on the interferometric SAR data; correcting the initial planar position coordinates according to the height of the ground object relative to the ground and the interferometric SAR data to obtain the corrected planar position coordinates; obtaining the corrected ground elevation corresponding to the coordinates according to the corrected planar position coordinates, correcting the height of the ground object relative to the ground to obtain the corrected elevation relative to the ground, obtaining the height of the ground object relative to the ground by using the interferometric SAR data, performing planar positioning position correction on the initial planar position coordinates through the height of the ground object relative to the ground, eliminating the error caused by local geometric distortion, and then obtaining the corresponding ground elevation through the corrected planar positioning position.

Description

Technical Field

[0001] The present invention relates to the technical field of remote sensing measurement, and particularly 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 environmental conditions, and is an important data source in remote sensing applications. However, since SAR acquires data by means of side-looking imaging, geometric distortion phenomena such as foreshortening and layover usually occur in SAR images, causing difficulties for subsequent applications of SAR images.

[0003] Existing SAR image correction methods include: 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 resampling the SAR image to the accurate geographical location, so as to achieve 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, and does not contain or does not accurately contain the height information of ground objects such as forests and buildings relative to the ground, and thus cannot correct the small-scale local geometric distortion caused by the height of ground objects relative to the ground surface (or DEM).

[0004] In addition, there is also true orthorectification assisted by high-precision DSM (Digital Surface Model) data. By calculating the true geographical location of ground object targets and using a specific resampling method to correct the local geometric distortion of ground objects, this method is usually applied to building areas. Since the SAR signal cannot penetrate buildings, the position in the SAR image can then be matched with the building elevation position provided by the DSM. However, this method is difficult to apply in forest areas because the SAR signal has a certain penetrability in forest areas, which 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 calculate the geographical location of forest targets based on this, and thus it is impossible to correct the SAR images of forest scenes. 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 of being unable to correct the small-scale local geometric distortion caused by the height of ground objects relative to the ground surface.

[0006] To solve the above problems, the present invention provides an interferometric SAR image correction method, including the following steps:

[0007] Step S1000: Obtain InSAR data and DTM data;

[0008] Step S2000: Construct an initial mapping relationship between the SAR slant range space and the geospatial space according to the InSAR data and the DTM data;

[0009] Step S3000: Obtain the height of the ground object relative to the ground according to the InSAR data ;

[0010] Step S4000: Correct the initial planar position coordinates and the InSAR data to obtain the corrected planar position coordinates ; ;

[0011] Step S5000: Obtain the corrected ground elevation corresponding to the coordinate according to the corrected planar position coordinates , correct the height of the ground object relative to the ground , and obtain the corrected ground elevation . .

[0012] Furthermore, in the above InSAR image correction method, the initial mapping relationship can be expressed by the following formula:

[0013] (1)

[0014] where and are the coordinates in the SAR slant range space, is the geospatial coordinate, where is the initial planar position coordinate, is the ground elevation.

[0015] Furthermore, in the above InSAR image correction method, step S4000 further includes:

[0016] Step S4100: Correct the initial mapping relationship to obtain an accurate mapping relationship.

[0017] Furthermore, in the above InSAR image correction method, the expression of the accurate mapping relationship in step S4100 is

[0018] (3).

[0019] Furthermore, in the above InSAR image correction method, after step S5000, it further includes:

[0020] Step S6000: Determine the image range of the geospatial area according to the precise mapping relationship, and obtain the coordinates of each geospatial pixel. , and calculate several slant-range spatial pixels that are closest to the geospatial pixel in the two-dimensional plane according to the precise mapping relationship, and count the ground-corrected elevations of the slant-range spatial pixels of the quantile height . According to the quantile height , correct the ground object height of the geospatial pixel to obtain the coordinates of the geospatial pixel .

[0021] Further, in the above interferometric SAR image correction method, after the step S5000, the following steps are further included:

[0022] Step S7000: Determine the image range of the geospatial area according to the precise mapping relationship, and obtain the coordinates of each geospatial pixel , and calculate several slant-range spatial pixels that are closest to the geospatial pixel in the three-dimensional distance according to the precise mapping relationship, and use the inverse distance weighted resampling method to calculate the image value of each slant-range spatial pixel as the image value of the geospatial pixel.

[0023] Further, in the above interferometric SAR image correction method, the interferometric SAR data is SAR image data in the slant-range space; the DTM data is a digital terrain model that only contains terrain elevation information.

[0024] Further, in the above interferometric SAR image correction method, the step S3000 specifically includes the following steps:

[0025] Step S3100: Perform interferometric processing on the interferometric SAR data and extract the interferometric phase information of the interferometric SAR data.

[0026] Step S3200: Remove the terrain phase information according to the initial mapping relationship and the interferometric SAR data, and extract the interferometric phase information of the ground elevation .

[0027] Step S3300: Realize the conversion of the interferometric phase and the height information according to the interferometric SAR imaging geometry, and obtain the height of the ground object relative to the ground .

[0028] Further, in the above interferometric SAR image correction method, the calculation formula of the correction value in the corrected plane position coordinates in the step S4000 is as follows:

[0029] (2)

[0030] Among them, is the radar view angle, is the angle between the side view direction of the radar and the due east direction, and are respectively the planar positioning deviations in the east-west direction and the north-south direction, is the height of the ground object relative to the ground.

[0031] Utilize the interferometric SAR data to obtain the height of the ground object relative to the ground, and through the height of the ground object relative to the ground correct the initial planar position coordinates to eliminate the error caused by local geometric distortion. Then, obtain the corresponding ground elevation through the corrected planar positioning position, thereby completing the calibration. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is the flowchart of the steps of the embodiment shown in the present invention;

[0033] Figure 2 is the schematic diagram of the remote sensing measurement calculation model of the embodiment shown in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0035] The following describes an interferometric SAR image calibration method shown in the present invention, referring to Figure 1 , and specifically includes the following steps:

[0036] Step S1000: Obtain interferometric SAR data and DTM (Digital Terrain Model) data. Specifically, the interferometric SAR data is the SAR image data in the slant range space (R), which needs to meet the ability to measure elevation information, while the 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.

[0037] Step S2000: Construct an initial mapping relationship between the SAR slant range space (R) and the geographic space (M) according to the interferometric SAR data and the DTM data. The initial mapping relationship can be expressed by the following formula:

[0038] (1)

[0039] Among them, and are the coordinates in the SAR slant range space, are the geospatial coordinates, where are the initial geocoding position coordinates, is the ground elevation.

[0040] Step S3000: Obtain the height of the ground object relative to the ground according to the interferometric SAR data , and the specific steps are as follows:

[0041] Step S3100: Perform interferometric processing on the interferometric SAR data and extract the interferometric phase information of the interferometric SAR data.

[0042] Step S3200: Remove the topographic phase information according to the initial mapping relationship and the interferometric SAR data, and extract the interferometric phase information of the ground elevation .

[0043] Step S3300: Realize the conversion between the interferometric phase information of the ground elevation and the height of the ground object relative to the ground to obtain the height of the ground object relative to the ground .

[0044] Step S4000: Correct the initial planar position coordinates according to the height of the ground object relative to the ground and the interferometric SAR data to obtain the corrected planar position coordinates , and the specific correction value calculation formula is as follows:

[0045] (2)

[0046] where is the radar viewing angle, is the angle between the radar side-looking direction and the due east direction, and are the planar positioning deviations in the east-west and north-south directions respectively, is the height of the ground object relative to the ground.

[0047] Step S4000 specifically further includes:

[0048] Step S4100: Then correct the initial mapping relationship to obtain the precise mapping relationship, and the calculation formula is as follows:

[0049] (3)

[0050] Step S5000: Obtain the corrected ground elevation corresponding to the corrected planar position coordinates ​ The height of the ground object relative to the ground is corrected to obtain the ground-corrected elevation , and the specific calculation formula is as follows:

[0051] (4)

[0052] To obtain a more accurate geometric position, after step S5000, step S6000 is further included.

[0053] Step S6000: Determine the image range of the geospatial according to the precise mapping relationship, obtain the coordinates of each geospatial pixel , and calculate several slant-range spatial pixels with the closest two-dimensional planar distance (i.e., the projected distance on the ROF plane in Figure 2 ) to the geospatial pixel according to the precise mapping relationship, and count the ground-corrected elevations of the slant-range spatial pixels of the quantile height , and correct the ground object height of the geospatial pixel according to the quantile height to obtain the coordinates of the geospatial pixel .

[0054] Similarly, to obtain a more accurate geometric position, after step S6000, step S7000 is further included.

[0055] Step S7000: Determine the image range of the geospatial according to the precise mapping relationship, obtain the coordinates of each geospatial pixel , and calculate several slant-range spatial pixels with the closest three-dimensional distance to the geospatial pixel according to the precise mapping relationship, and use the inverse distance weighted resampling method to calculate the SAR intensity, interferometric SAR coherence and other image values of each slant-range spatial pixel as the image values of the geospatial pixel.

[0056] Next, in combination with Figure 2 the working principle of this embodiment will be described. In the figure, ON represents the due north direction, OE represents the due east direction, OH represents the elevation direction, OF represents the radar flight direction, and OR represents the projection vector of the radar side-looking direction on the plane; the angle between the radar beam center and the vertical direction, that is, the radar viewing angle ; A * The point corresponds to the top position of a tree, and point A corresponds to the SAR signal observation position. Since the SAR signal has a certain penetration, point A is generally lower than A * point. The height of point A relative to its ground point C is denoted as the ground-corrected elevation , The distances of point A and point B from the radar are equal (slant ranges are equal). Thus, based on the geocoding of DTM data, the radar will mistake the position of point A for point B during the measurement process and correction is needed to obtain the true position.

[0057] Obtain the three-dimensional coordinates of point B through the initial mapping relationship between the SAR slant range space (R) and the geographic space (M). It can be assumed that the three-dimensional coordinates of point B are: , The initial planar position coordinates have errors. Meanwhile, 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 at this time. Among them, the error of the initial planar position coordinates causes the planar positioning deviation due to local geometric distortion and needs to be corrected in subsequent steps. Through the height of the ground object relative to the ground correct the initial planar position coordinates , and the error caused by local geometric distortion can be eliminated. The height AD of point A relative to point B, that is, the height of the ground object measured by SAR relative to the ground , can be obtained through the interferometric SAR data . Then, the planar coordinates of point B can be corrected first. Thus, the coordinates of point A can be corrected to: . Then obtain the height of point C relative to B, that is, the ground corrected elevation of point C When obtaining the height of point C relative to B through the interferometric SAR data, that is, the ground elevation of point C . Meanwhile, since point C is directly below point A, the ground corrected elevation corresponding to this coordinate can be obtained through the planar position coordinates of point A , that is, the height of point C relative to point D. Thus, the height of point A relative to point C (that is, the ground corrected elevation ) can be calculated. Finally, the coordinates of point A are corrected to: .

[0058] The trees in the forest area will grow gradually over time. The DTM data is the elevation data for the terrain / ground and cannot update the height data of the trees after growth. Through the technical solution in this scheme, the relative height data of the trees can be updated in a timely manner.

[0059] It should be understood that the above specific embodiments of the present invention are only used for exemplary illustration or explanation of the principle of the present invention and do not constitute a limitation to the present invention. Therefore, any modifications, equivalent replacements, improvements, etc. made without departing from the spirit and scope of the present invention shall be included within the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all variations and modification examples falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. An interferometric SAR image correction method, characterized in that, Including the following steps: Step S1000: Obtain interferometric SAR data and DTM data; Step S2000: Construct an initial mapping relationship between the SAR slant range space and the geospatial space according to the interferometric SAR data and the DTM data; The initial mapping relationship can be expressed by the following formula: （1） Among them, and are the coordinates in the SAR slant range space, is the said geospatial coordinate, where is the initial planar position coordinate, is the ground elevation; Step S3000: Obtain the height of the ground object relative to the ground based on the interferometric SAR data ; Step S4000: According to the height of the feature relative to the ground and the interferometric SAR data, correct the initial planar position coordinates to obtain the corrected planar position coordinates , where and are the planar positioning deviations in the east-west direction and the north-south direction respectively; Step S5000: According to the corrected planar position coordinates Obtain the ground-corrected elevation corresponding to this coordinate , and correct the height of the ground object relative to the ground to obtain the ground-corrected elevation . The calculation formula is: （4） Among them, is the ground elevation.

2. The interferometric SAR image correction method according to claim 1, characterized in that: The step S4000 further includes: Step S4100: Modify the initial mapping relationship to obtain an accurate mapping relationship.

3. The interferometric SAR image correction method according to claim 2, characterized in that: The expression of the accurate mapping relationship in the step S4100 is （3）。 4. The interferometric SAR image correction method according to claim 2, characterized in that: After the step S5000, it further includes: Step S6000: Determine the image range of the geospatial area according to the precise mapping relationship, and obtain the coordinates of each geospatial pixel , and calculate several slant range pixels that are closest to the two-dimensional plane of the geospatial pixel according to the precise mapping relationship, and count the ground-corrected elevation of the slant range pixels of the quantile height , according to the quantile height correct the ground object height of the geospatial pixel to obtain the coordinates of the geospatial pixel .

5. The interferometric SAR image correction method according to claim 4, characterized in that: After the step S6000, it further includes: Step S7000: Determine the image range of the geospatial area according to the precise mapping relationship, and obtain the coordinates of each geospatial pixel , and calculate several slant range space pixels that are three-dimensionally closest to the geospatial pixel according to the precise mapping relationship. Use the inverse distance weighted resampling method to calculate the image value of each slant range space pixel as the image value of the geospatial pixel.

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

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

8. The interferometric SAR image correction method according to claim 1, characterized in that: The corrected planar position coordinates in the step S4000 The correction value calculation formula therein is as follows: （2） Among them, is the radar view angle, is the angle between the radar side view direction and the due east direction, and are respectively the planar positioning deviations in the east-west direction and the north-south direction, is the height of the ground object relative to the ground.

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