Multi-baseline InSAR residual phase error correction method and system based on flat ground prior information

Abstract

The invention provides a multi-baseline InSAR residual phase error correction method and system based on flat ground prior information, and the method comprises the steps: selecting a large flat ground region and a small flat ground region for the terrain prior knowledge of a research region, constructing a residual linear phase model, removing the residual linear error phase of a multi-baseline InSAR interferometric phase, and carrying out the correction of the multi-baseline InSAR residual phase error. The function of improving the phase error accuracy and the correction speed of the multi-baseline InSAR is achieved. According to the method, the correction precision of the interference phase of the multi-baseline InSAR after flat ground removal is improved, the phase error correction precision under the condition of small baselines is high, and the terrain reconstruction precision of the multi-baseline InSAR is high; and a reliable data basis is provided for accurate reconstruction of the multi-baseline InSAR terrain. According to the method, the speed of the error phase correction process is high, and the consumption of computing resources and the hardware cost of the system are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of interferometric synthetic aperture radar data processing, and in particular relates to a multi-baseline InSAR residual phase error correction method and system based on flat ground prior information. Background Art

[0002] Interferometric Synthetic Aperture Radar (InSAR) is an image geodetic technology that has developed rapidly in recent years. It uses SAR image data observed from different perspectives to map the surface topography. Multi-baseline InSAR combines SAR image data observed from multiple different perspectives to form a virtual aperture at a high altitude, achieving three-dimensional reconstruction of the surface topography and greatly improving the accuracy of terrain elevation measurement. Therefore, multi-baseline InSAR has become a reliable means of current InSAR topographic mapping. For example, the four-satellite network of Hongtu-1 forms a multi-baseline InSAR system, which realizes accurate three-dimensional reconstruction of complex surface topography around the world.

[0003] However, in the process of data acquisition, multi-baseline InSAR is usually susceptible to deterministic errors caused by factors such as baseline error, calibration error, InSAR system errors, and atmospheric delay. If these deterministic errors are not eliminated, the height measurement accuracy and even the success of multi-baseline InSAR will be seriously restricted. Therefore, phase error correction is one of the key technologies of multi-baseline InSAR.

[0004] There are a large number of phase error correction methods based on coherence measurement criteria, which calculate the residual error phase pixel by pixel along multiple baseline dimensions, update the terrain reconstruction information at the same time, and alternately iterate and optimize to solve the residual error phase and terrain height. This type of method requires a large number of interference patterns and an accurate residual error phase model assumption, and the residual phase error correction speed is slow; moreover, when the number of interference patterns is small and the target signal-to-noise ratio is low, the residual phase error correction accuracy is low.

[0005] The phase error of InSAR caused by system errors, atmospheric delays and other factors is usually linearly related to distance and azimuth, while the real interferometric phase on flat ground is usually close to zero. Therefore, it is urgent to propose a new method for multi-baseline InSAR residual phase error correction to improve the speed of phase error correction and the accuracy of phase error correction under small baseline conditions. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a multi-baseline InSAR residual phase error correction method and system based on flat ground prior information, so as to improve the multi-baseline InSAR phase error accuracy and correction speed.

[0007] The technical solution adopted by the present invention to solve the above technical problems is: a multi-baseline InSAR residual phase error correction method based on flat ground prior information, comprising the following steps:

[0008] S1: Acquire multi-baseline InSAR images and perform interferometric preprocessing to obtain the multi-baseline InSAR interferometric phase after flattening;

[0009] S2: removing the residual linear error phase of the multi-baseline InSAR interferometric phase after the flattening, and obtaining the multi-baseline InSAR interferometric phase after the phase error is corrected; the specific steps include:

[0010] S21: selecting a window flat area in the flat area based on prior knowledge;

[0011] S22: the main part of the residual linear error phase of the multi-baseline InSAR interferometric phase after removing the flat ground in the window flat ground area;

[0012] S23: removing the remaining part of the residual linear error phase of the multi-baseline InSAR interferometric phase after removing the flat ground in the flat ground area;

[0013] S3: Reconstruct multi-baseline InSAR terrain or three-dimensionally reconstruct tomographic SAR point cloud based on the multi-baseline InSAR interferometric phase after correcting the phase error.

[0014] According to the above scheme, in step S1, the interference preprocessing includes selecting a main image, multi-baseline SAR image registration, generating an interference phase, and removing the flat ground interference phase from the interference phase.

[0015] According to the above scheme, in step S2, the residual linear error phase includes InSAR system error, baseline error and atmospheric delay.

[0016] According to the above scheme, in step S21, the specific steps are:

[0017] According to the prior knowledge of the terrain in the study area, the multi-baseline InSAR interferometric phase is used to delineate the same flat area, and the same window flat area is selected from the flat area.

[0018] Furthermore, in step S22, the specific steps are:

[0019] S221: Construct a residual linear phase model to fit the parameters of the residual linear phase in the multi-baseline InSAR interferometric phase after removing the flat ground in the window flat ground area;

[0020] S222: Substitute the parameters of the residual linear phase fitted in the window flat area into the residual linear phase model to solve the residual linear phase of all pixels of the multi-baseline InSAR interferometric phase;

[0021] S223: Subtract the residual linear phase obtained in step S222 from the multi-baseline InSAR interferometry phase after the flattening to remove the main part of the residual linear phase in the multi-baseline InSAR interferometry phase, and obtain the multi-baseline InSAR interferometry phase of the remaining part of the residual linear phase.

[0022] Furthermore, in step S23, the specific steps are:

[0023] S231: Parameters of residual linear phase in multi-baseline InSAR interferometric phase after fitting the flat ground in the flat ground area;

[0024] S232: Substituting the parameters of the residual linear phase fitted in the flat area into the residual linear phase model, and solving the residual linear phase of all pixels of the multi-baseline InSAR interferometric phase image for the remaining part of the residual linear phase;

[0025] S233: Subtract the residual linear phase obtained in step S232 from the residual linear phase in the multi-baseline InSAR interferometry phase after leveling to remove the error of the multi-baseline InSAR interferometry phase of the remaining residual linear phase, and obtain the multi-baseline InSAR interferometry phase after the phase error is corrected.

[0026] According to the above scheme, in step S22, the parameters of the fitted residual linear phase include the first-order term coefficients along the range direction, the first-order term coefficients along the azimuth direction and the constant term parameters.

[0027] A multi-baseline InSAR residual phase error correction system based on flat ground prior information comprises a preprocessing module, a phase error correction module and a terrain reconstruction module; the preprocessing module is used to acquire a multi-baseline InSAR image and perform interference preprocessing to obtain a multi-baseline InSAR interference phase after removing the flat ground; the phase error correction module is used to remove the residual linear error phase of the multi-baseline InSAR interference phase after removing the flat ground to obtain a multi-baseline InSAR interference phase after correcting the phase error; the terrain reconstruction module is used to reconstruct a multi-baseline InSAR terrain or a three-dimensional reconstruction of a tomographic SAR point cloud based on the multi-baseline InSAR interference phase after correcting the phase error.

[0028] Furthermore, the phase error correction module includes a flat bottom area selection module, an error phase main component removal module and an error phase residual component removal module; the flat bottom area selection module is used to select a flat ground area and a window flat ground area in the flat ground area based on prior knowledge; the error phase main component removal module is used to remove the main component of the residual linear error phase of the multi-baseline InSAR interference phase after the flat ground is removed in the window flat ground area; the error phase residual component removal module is used to remove the residual component of the residual linear error phase of the multi-baseline InSAR interference phase after the flat ground is removed in the flat ground area.

[0029] Furthermore, the invention also comprises a memory storing a computer program executable by a computer processor, wherein the computer program executes a multi-baseline InSAR residual phase error correction method based on flat ground prior information.

[0030] The beneficial effects of the present invention are:

[0031] 1. The present invention provides a multi-baseline InSAR residual phase error correction method and system based on flat land prior information. By selecting large and small flat land areas based on the terrain prior knowledge of the study area, a residual linear phase model is constructed. The residual linear error phase of the multi-baseline InSAR interferometric phase is removed with less map size and correction times, thereby achieving the function of improving the multi-baseline InSAR phase error accuracy and correction speed.

[0032] 2. The present invention improves the correction accuracy of the multi-baseline InSAR interferometry phase after leveling, has high phase error correction accuracy in the case of small baselines, and has high accuracy in multi-baseline InSAR terrain reconstruction; it provides a reliable data basis for accurate reconstruction of multi-baseline InSAR terrain.

[0033] 3. The error phase correction process of the present invention is fast, which reduces the consumption of computing resources and the hardware cost of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a flow chart of an embodiment of the present invention.

[0035] Figure 2 is any interference phase diagram generated by simulation in an embodiment of the present invention.

[0036] Figure 3 This is an interference phase diagram after ground flattening according to an embodiment of the present invention. Figure 4 This is an interference phase diagram of an embodiment of the present invention in which most of the residual linear errors are removed. Figure 5 This is an interference phase diagram of an embodiment of the present invention with residual tiny linear errors removed. Figure 6This is a topographic result map of multi-baseline InSAR reconstruction after phase error correction according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0038] Example 1

[0039] See also Figure 1 , this embodiment includes the following steps:

[0040] Step 1: Acquire SAR data and ephemeris parameters collected by multiple radar antennas or multiple passes; perform interferometric preprocessing on multi-baseline SAR images, including selecting the main image, multi-baseline SAR image registration, generating interferometric phases, and removing the flat ground interferometric phases from the interferometric phases, thereby obtaining the multi-baseline InSAR interferometric phases after the flat ground is removed;

[0041] Step 2: Remove the residual linear error phase caused by InSAR baseline error, baseline error and atmospheric delay in the multi-baseline InSAR interferometric phase after flattening. The specific steps are as follows:

[0042] Step 2.1: Based on the prior knowledge of the terrain in the study area, the multi-baseline InSAR interferometric phase is used to delineate the same large and wide flat area R2, and select the same small flat area R1 from it;

[0043] Step 2.2: Construct the following residual linear phase model

[0044]

[0045] in is the ideal residual phase error caused by baseline error, interferometric calibration error and atmospheric delay error, x and y are the range and azimuth indices respectively, a and b are the linear coefficients, c is the constant term, ∈ is the random noise phase, and φ is the interferometric phase after de-flattening.

[0046] Based on equation (1), we extrapolate to any single baseline InSAR interferometric phase after removing the flat ground, and combine the interferometric phases of all M pixels in the R1 region to obtain the interferometric phase equation after removing the flat ground:

[0047]

[0048] Using the least squares method, that is, formula (3)

[0049]

[0050] Solve the parameters of most of the residual linear phase in the R1 region, that is, along the distance Azimuthal coefficient of the first order term And constant parameters

[0051] Step 2.3: Substitute the parameters solved in step 2.2 Substituting all pixels, the residual interference phase error fitted under the baseline situation is obtained, that is,

[0052]

[0053] in is the fitted residual interference phase of all pixels of the baseline interference phase; the interference phase after flattening is subtracted from the fitted residual interference phase to obtain the interference phase with most of the residual linear phase removed in the baseline case; similarly, it is extrapolated to all multi-baseline InSAR interference phase cases to obtain the multi-baseline InSAR interference phase with most of the residual linear phase removed.

[0054] Step 2.4: For any small residual linear phase remaining in the multi-baseline InSAR interferometric phase in step 2.3, extrapolate steps 2.2 and 2.3 to step 2.4.

[0055] First, similar to step 2.2, the interference phases of all pixels in the R2 region are combined to obtain the interference phase equation after flattening. The least squares method is used to solve the parameters of the small part of the residual linear phase in the R2 region, namely the first-order coefficient b2 along the distance direction a2 and the azimuth direction and the constant term parameter c2.

[0056] Next, the solved a2, b2, and c2 parameters are substituted into all pixels to obtain the small residual interference phase error fitted under this baseline situation, and the small residual linear phase error of the multi-baseline InSAR interferometric phase from which most of the residual linear phase has been removed in step 2.3 is accurately removed to obtain the multi-baseline InSAR interferometric phase with accurately corrected residual linear error.

[0057] Step 3: The multi-baseline InSAR interferometric phase with accurate phase error correction is used for multi-baseline InSAR terrain reconstruction or tomographic SAR point cloud 3D reconstruction.

[0058] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0059] Example 2

[0060] This embodiment adopts the steps of embodiment 1 to calibrate and simulate 20 Ku-band SAR data of the Bird's Nest building, generating 19 interferometric phase images. Figure 2is any one of the interference phase diagrams; Figure 3 This is the interference phase diagram after removing the flat ground. It can be seen that after removing the flat ground, the fringes in the flat ground area are effectively removed; Figure 4 The interferometric phase diagram in which most of the residual linear errors are removed by using step 2.3 of the present invention; Figure 5 The interferometric phase image after removing the residual tiny linear error by step 2.4 of the present invention shows that after the phase error correction of the present invention, the interferometric phase in the flat area is calibrated to near zero, indicating that the accuracy of the multi-baseline InSAR interferometric phase error correction of the present invention is high.

[0061] In addition, the time taken to correct the residual phase errors of 19 multi-baseline interferometric phase images using this embodiment does not exceed 1 minute. Figure 6 The terrain results reconstructed using multi-baseline InSAR technology show that the flat land and building heights are effectively restored.

[0062] The above embodiments are only used to illustrate the design ideas and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, any equivalent changes or modifications made based on the principles and design ideas disclosed by the present invention are within the protection scope of the present invention.

Claims

1. A multi-baseline InSAR residual phase error correction method based on flat ground prior information, characterized by: The following steps are involved: S1: Acquire multi-baseline InSAR images and perform interferometric preprocessing to obtain the multi-baseline InSAR interferometric phase after flattening; S2: removing the residual linear error phase of the multi-baseline InSAR interferometric phase after the flattening, and obtaining the multi-baseline InSAR interferometric phase after the phase error is corrected; the specific steps include: S21: based on the prior knowledge of terrain and the interference phase fringe information, selecting the flat area and the window flat area in the flat area; S22: the main part of the residual linear error phase of the multi-baseline InSAR interferometric phase after removing the flat ground in the window flat ground area; S23: removing the remaining part of the residual linear error phase of the multi-baseline InSAR interferometric phase after removing the flat ground in the flat ground area; S3: Reconstruct multi-baseline InSAR terrain or three-dimensionally reconstruct tomographic SAR point cloud based on the multi-baseline InSAR interferometric phase after correcting the phase error.

2. The multi-baseline InSAR residual phase error correction method based on flat ground prior information according to claim 1, characterized in that: In the step S1, the interference preprocessing includes selecting a main image, multi-baseline SAR image registration, generating an interference phase, and removing the flat ground interference phase from the interference phase.

3. The multi-baseline InSAR residual phase error correction method based on flat ground prior information according to claim 1, characterized in that: In step S2, the residual linear error phase includes InSAR system error, baseline error and atmospheric delay.

4. The multi-baseline InSAR residual phase error correction method based on flat ground prior information according to claim 1, characterized in that: In the step S21, the specific steps are: According to the prior knowledge of the terrain in the study area and the interferometric phase fringe information, the same flat area is delineated for the area without phase jump in the multi-baseline InSAR interferometric phase, and the same window flat area is selected from the flat area.

5. The multi-baseline InSAR residual phase error correction method based on flat ground prior information according to claim 4, characterized in that: In the step S22, the specific steps are: S221: Construct a residual linear phase model to fit the parameters of the residual linear phase in the multi-baseline InSAR interferometric phase after removing the flat ground in the window flat ground area; S222: Substitute the parameters of the residual linear phase fitted in the window flat area into the residual linear phase model to solve the residual linear phase of all pixels of the multi-baseline InSAR interferometric phase; S223: Subtract the residual linear phase obtained in step S222 from the multi-baseline InSAR interferometry phase after the flattening to remove the main part of the residual linear phase in the multi-baseline InSAR interferometry phase, and obtain the multi-baseline InSAR interferometry phase of the remaining part of the residual linear phase.

6. The multi-baseline InSAR residual phase error correction method based on flat ground prior information according to claim 5, characterized in that: In the step S23, the specific steps are: S231: Parameters of residual linear phase in multi-baseline InSAR interferometric phase after fitting the flat ground in the flat ground area; S232: Substituting the parameters of the residual linear phase fitted in the flat area into the residual linear phase model, and solving the residual linear phase of all pixels of the multi-baseline InSAR interferometric phase image for the remaining part of the residual linear phase; S233: Subtract the residual linear phase obtained in step S232 from the residual linear phase in the multi-baseline InSAR interferometry phase after leveling to remove the error of the multi-baseline InSAR interferometry phase of the remaining residual linear phase, and obtain the multi-baseline InSAR interferometry phase after the phase error is corrected.

7. The multi-baseline InSAR residual phase error correction method based on flat ground prior information according to claim 1, characterized in that: In the step S22, the parameters of the fitted residual linear phase include the first-order term coefficients along the range direction, the first-order term coefficients along the azimuth direction and the constant term parameters.

8. A multi-baseline InSAR residual phase error correction system based on flat ground prior information, characterized in that: It includes a pre-processing module, a phase error correction module and a terrain reconstruction module; The preprocessing module is used to acquire multi-baseline InSAR images and perform interferometric preprocessing to obtain the multi-baseline InSAR interferometric phase after flattening. The phase error correction module is used to remove the residual linear error phase of the multi-baseline InSAR interferometric phase after the ground is leveled, and obtain the multi-baseline InSAR interferometric phase after the phase error is corrected; The terrain reconstruction module is used to reconstruct multi-baseline InSAR terrain or three-dimensionally reconstruct tomographic SAR point cloud based on the multi-baseline InSAR interferometric phase after correcting the phase error.

9. The multi-baseline InSAR residual phase error correction system based on flat ground prior information according to claim 8, characterized in that: The phase error correction module includes a flat bottom area selection module, an error phase main component removal module and an error phase residual component removal module; The flat bottom area selection module is used to select the flat ground area and the window flat ground area in the flat ground area based on prior knowledge; The error phase main component removal module is used to remove the main component of the residual linear error phase of the multi-baseline InSAR interferometric phase after the flat ground is removed in the window flat ground area; The error phase residual component removal module is used to remove the residual components of the residual linear error phase of the multi-baseline InSAR interferometric phase after the flat ground is removed in the flat ground area.

10. The multi-baseline InSAR residual phase error correction system based on flat ground prior information according to claim 8, characterized in that: The invention also comprises a memory storing a computer program executable by a computer processor, wherein the computer program executes the multi-baseline InSAR residual phase error correction method based on flat ground prior information as claimed in any one of claims 1 to 7.

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