Inter-satellite scattering mutual interference detection method based on polarization characteristics

Abstract

The invention discloses a polarization characteristic-based inter-satellite scattering mutual interference detection method, which comprises the following steps of: synchronously dividing an echo matrix of a cross polarization channel and an echo matrix of a co-polarization channel of a satellite-borne SAR (Synthetic Aperture Radar) in a dual-polarization mode into a plurality of echo matrix blocks along an azimuth direction, and on the basis of an incoherent accumulation result and a relative entropy, carrying out inter-satellite scattering mutual interference detection on the echo matrix blocks; determining echo matrix blocks containing MTSI interference, and calculating the energy of each row; clustering the pulses based on energy, screening out interference pulses containing MTSI, and generating an initial interference mask; constructing a polarizability index sequence for each interference pulse containing the MTSI; according to the polarizability index sequence, positioning an area where the MTSI interference is located in each MTSI-containing interference pulse based on a self-adaptive threshold value; and according to positioning results of all MTSI interferences, updating the initial interference mask to obtain a final time domain interference mask, and completing interference detection. According to the invention, high-precision positioning of MTSI interference in spaceborne SAR echo data can be realized, and improvement of the anti-interference capability of a spaceborne SAR system is facilitated.

Description

Technical Field

[0001] This invention belongs to the field of radar signal processing, specifically relating to a method for detecting inter-satellite scattering interference based on polarization characteristics, which is applicable to detecting inter-satellite scattering interference (MTSI) signals in raw echo data of spaceborne synthetic aperture radar. Background Technology

[0002] Spaceborne Synthetic Aperture Radar (SAR) possesses all-weather, all-day Earth observation capabilities and is widely used in resource exploration, topographic mapping, and disaster early warning. With the ever-expanding demand for spectrum bandwidth from information applications, the supply-demand imbalance between limited spectrum resources is becoming increasingly prominent. Spaceborne SAR systems inevitably suffer from radio frequency interference (RFI) from other electromagnetic radiation sources in the same frequency band. RFI can be categorized into direct ground interference (RDI) and mutual ground scattering interference (MTSI). The main sources of RFI are high-power wireless devices shared in the same frequency band on the ground or sea surface, such as radio communication equipment and radio navigation systems. MTI, on the other hand, is interference signals generated by ground scattering from different radar remote sensing satellites in scenarios where time, space, and frequency overlap. Interference directly affects the echo signal acquisition process, disrupts the amplitude and phase of images, and significantly reduces image quality and the reliability of subsequent derivative products. Therefore, it is necessary to study reliable and refined interference suppression methods.

[0003] Traditional interference detection methods primarily utilize the rate of change, differences, and regional connectivity between image pixels, or calculate statistical quantities such as skewness and kurtosis to obtain a threshold that can effectively separate interference from useful data. Inter-satellite scattering interference (MSI) signals and SAR target echo signals have similar transmit power and propagation paths, resulting in no significant energy difference and low feature distinguishability between them. Furthermore, severe aliasing occurs in the time-frequency representation space, making it difficult for traditional detection methods to effectively detect MSI. Current detection of MTSI mainly utilizes its unique texture patterns, shapes, and modes exhibited in multiple dimensions, including the time domain, frequency domain, and image domain. These methods include detection methods based on out-of-band spectral energy and detection methods based on maximum eigenvalue sequences. These approaches focus on using the time-domain and frequency-domain features of MSI to locate its azimuthal position, lacking research on MTSI range-direction location. In addition, existing research has not sufficiently explored the feature mining of MTSI in the polarization domain. Summary of the Invention

[0004] In view of the different characteristics of MTSI under different polarization modes, this invention provides an inter-satellite scattering interference detection method based on polarization features, which can realize high-precision positioning of MTSI interference in spaceborne SAR echo data, provide reliable prior information for subsequent refined interference suppression, and help improve the anti-interference capability of spaceborne SAR system.

[0005] To achieve the above objectives, the present invention employs the following technical solution: An inter-satellite scattering interference detection method based on polarization characteristics includes: The echo matrix of the cross-polarization channel and the echo matrix of the same polarization channel of the spaceborne SAR in dual polarization mode are synchronously divided into multiple echo matrix blocks along the azimuth direction. For each echo matrix block in the cross-polarization channel and the co-polarization channel, the echo data are incoherently accumulated along the range direction; the corresponding relative entropy is calculated based on the incoherent accumulation results, and the echo matrix block containing MTSI interference is determined using the relative entropy; For each echo matrix block containing MTSI interference, calculate the energy of each pulse contained therein; For all pulses in the echo matrix block containing MTSI interference, cluster them according to their energy to filter out pulses containing MTSI interference and generate an initial interference mask; For each pulse containing MTSI interference, its polarizability index is calculated sequentially using a sliding window to construct a polarizability index sequence; Based on the polarimetric index sequence of pulses containing MTSI interference, the region where MTSI interference is located in each pulse containing MTSI interference is located using an adaptive threshold. Based on the location results of all MTSI interferences, the initial interference mask is updated to obtain the final temporal interference mask, thus completing the interference detection.

[0006] Furthermore, the corresponding relative entropy is calculated based on the incoherent accumulation results, including: ; in, This indicates the first term of the cross-polarization channel and the co-polarization channel. Each echo matrix is ​​divided into blocks. , The relative entropy, and They represent , The result of incoherent accumulation along the distance, i Represents the azimuth sampling point number. , Indicates rounding down. This indicates the total number of sampling points in the azimuth direction. This represents the number of echo matrix blocks divided into cross-polarization channels and co-polarization channels.

[0007] Furthermore, the echo matrix blocks containing MTSI interference are determined using relative entropy, including: Set an entropy threshold; when the cross-polarized channel and the same-polarized channel... Each echo matrix is ​​divided into blocks. , When the relative entropy is greater than the entropy threshold, it indicates that... or MTSI interference echoes exist; then, calculations are performed separately. , The variance of all incoherent cumulative results is calculated; the two variances are compared, and the echo matrix block corresponding to the larger variance is determined as the echo matrix block containing MTSI interference.

[0008] Furthermore, for all pulses in the echo matrix block containing MTSI interference, clustering is performed based on their energy to filter out pulses containing MTSI interference, and an initial interference mask is generated, including: The K-means clustering algorithm is used to cluster the energy of all pulses to obtain multiple clusters. The mean energy of the center of all clusters is calculated. Then, for each cluster, if the energy of the center of the cluster is higher than the mean, the cluster is regarded as a cluster containing MTSI interference, and all pulses contained therein are MTSI interference pulses. The remaining clusters are interference-free pulse clusters, and all pulses contained therein are interference-free pulses. Finally, for the echo matrix containing MTSI interference, the data in the row containing MTSI interference pulses is set to 1, and the data in the row without interference pulses is set to 0, thus obtaining the initial interference mask.

[0009] Furthermore, for each pulse containing MTSI interference, a sliding window is used to calculate its polarizability index sequentially, constructing a polarizability index sequence, including: Set the length and sliding step of the sliding window; starting from the beginning position of the pulse containing MTSI interference, calculate the polarimetric index of the echo data contained in each sliding window; after the sliding window reaches the end of the pulse containing MTSI interference according to the sliding step, the polarimetric index sequence composed of the polarimetric index calculated for each sliding window can be obtained.

[0010] Furthermore, the formula for calculating the polarizability index within each sliding window is as follows: ; in ,when This corresponds to a completely nonpolarized wave. Corresponding to fully polarized waves; , , , These are the four components of the Stokes vector.

[0011] Furthermore, based on the polarimetric index sequence of the MTSI interference pulses, the region containing the MTSI interference in each MTSI interference pulse is located using an adaptive threshold, including: Adaptive threshold Represented as: ;in and These represent the mean and variance of the polarization indices for all interference-free pulses in the echo matrix block containing MTSI interference, respectively. For each pulse containing MTSI interference, its polarization index sequence is compared with an adaptive threshold. The comparison is made by placing polarizability indices below this adaptive threshold. The positions of all sliding windows are determined to be the areas where MTSI interference occurs.

[0012] Furthermore, based on the localization results of all MTSI interferences, the initial interference mask is updated to obtain the final temporal interference mask, including: For each row containing MTSI interference pulses in the initial interference mask, the non-MTSI interference regions in that row are set to 0, thus obtaining the final time-domain interference mask, where the position of 1 is the position of MTSI interference.

[0013] A terminal device includes a processor, a memory, and a computer program stored in the memory; when the processor executes the computer program, it implements the inter-satellite scattering interference detection method based on polarization characteristics.

[0014] A computer-readable storage medium storing a computer program; when executed by a processor, the computer program implements the inter-satellite scattering interference detection method based on polarization characteristics.

[0015] Compared with the prior art, the present invention has the following technical features: Compared to traditional interference detection methods, this invention utilizes the energy characteristics and polarizability index of MTSI, based on the differences in characteristics exhibited by MTSI under different polarization modes, to effectively filter out pulse signals containing MTSI from spaceborne SAR echo data, accurately locate the range position of MTSI, generate a time-domain interference mask, and achieve reliable detection of MTSI. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the method flow in an embodiment of the present invention; Figure 2The following are the noncoherent accumulation results of the echo matrix blocks along the range direction in the embodiments of the present invention; where (a) is the VH polarization mode (including MTSI), (b) is the VV polarization mode (including MTSI), (c) is the VH polarization mode (without interference), and (d) is the VV polarization mode (without interference). Figure 3 This is the initial interference mask generated in the embodiments of the present invention; Figure 4 The following are the MTSI interference range-directed location results containing MTSI interference pulses in the embodiments of the present invention; wherein (a) is the MTSI interference location result of pulse one, (b) is the time-frequency diagram of pulse one, (c) is the interference location result of pulse two, and (d) is the time-frequency diagram of pulse two. Figure 5 This is the final temporal interference mask in the embodiments of the present invention. Detailed Implementation

[0017] Spaceborne SAR can employ various polarization methods when transmitting signals, commonly including horizontal (H) polarization and vertical (V) polarization. Spaceborne SAR can operate in single-polarization mode and dual-polarization mode. In dual-polarization mode, the two channels are called cross-polarization channel and co-polarization channel, respectively. Co-polarization channel refers to the combination of transmitting and receiving polarizations that are the same, including HH and VV. Cross-polarization channel refers to the combination of transmitting and receiving polarizations that are different, including VH and HV. VH represents V-polarization transmission and H-polarization reception. Here, VH represents vertical transmission and horizontal reception. The meanings of HH, VV, and HV follow the same pattern.

[0018] Step 1: Obtain the echo matrix of the cross-polarization channel of the spaceborne SAR in dual-polarization mode. echo matrix of the same polarization channel Synchronous division along the azimuth direction into The echo matrix is ​​divided into blocks; then the echo matrix is... and It can be represented as: (1); in, , These represent the first and second polarization channels, respectively. Each echo matrix is ​​divided into blocks. ; and They are respectively represented as , The i line, number j Echo data, , ; iRepresents the azimuth sampling point number. j Indicates the distance to the sampling point number. This indicates the total number of sampling points in the azimuth direction. This indicates the total number of sampling points in the distance direction. Indicates the first Total number of azimuth sampling points for each echo matrix block ， Indicates rounding down. express 3D complex space.

[0019] Step 2: Perform incoherent accumulation of each echo data in each echo matrix block of the cross-polarization channel and the co-polarization channel along the range direction; calculate the corresponding relative entropy based on the incoherent accumulation results, and use the relative entropy to determine the echo matrix block containing MTSI interference.

[0020] For cross-polarization channels and homopolarization channels, the first Each echo matrix is ​​divided into blocks. , , its first i line, number j Echo data and Incoherent accumulation along the range direction is performed as follows: (2); in and These represent the first and second polarization channels, respectively. The result of incoherent accumulation of each echo matrix block along the range direction.

[0021] Then the echo matrix is ​​calculated in blocks. , The relative entropy between them, based on the relative entropy sieve from the echo matrix and The echo matrix containing MTSI interference is selected as a block; specifically, this scheme sets an entropy threshold of 10. -3 When the relative entropy is greater than the set entropy threshold, it indicates that the echo matrix is ​​divided into blocks. or MTSI interference echoes are present; therefore, the echo matrix is ​​calculated in blocks. All incoherent cumulative results The variance was calculated, and the echo matrix was divided into blocks. All incoherent cumulative results The variance of the two variances is compared, and the echo matrix block corresponding to the larger variance is determined as the echo matrix block containing MTSI interference.

[0022] Relative entropy is used to measure the degree of difference between two probabilities, and can be expressed as: (3); Through filtering, one or more echo matrix blocks containing MTSI interference are obtained.

[0023] Step 3: For each echo matrix block containing MTSI interference, calculate the energy of each pulse (i.e., each row) contained therein.

[0024] Let the echo matrix containing MTSI interference be represented in blocks as follows: The echo matrix may be divided into blocks as follows: or ;but No. The energy of the corresponding pulse is represented as: (4); in express The i line, number j Echo data.

[0025] Step 4: For all pulses in the echo matrix block containing MTSI interference, cluster them according to their energy to filter out pulses containing MTSI interference and generate an initial interference mask.

[0026] Specifically, the K-means clustering algorithm is used to analyze the energy of all pulses. After clustering, multiple clusters are obtained; the mean energy of the center of all clusters is calculated; then for each cluster, if the energy of the center of the cluster is higher than the mean, the cluster is regarded as a cluster containing MTSI interference, and all pulses contained therein are MTSI interference pulses; the remaining clusters are interference-free pulse clusters, and all pulses contained therein are interference-free pulses.

[0027] Finally, for the echo matrix containing MTSI interference, the data in the row containing the MTSI interference pulses is set to 1, and the data in the row without interference pulses is set to 0, thus obtaining the initial interference mask. .

[0028] Step 5: For each pulse containing MTSI interference, calculate its polarizability index sequentially using a sliding window to construct a polarizability index sequence.

[0029] Set the length of the sliding window to The sliding step size is 100. Starting from the beginning of the MTSI interference pulse, the polarimetric index of the echo data contained in each sliding window is calculated. After the sliding window reaches the end of the MTSI interference pulse according to the sliding step size, the polarimetric index sequence calculated for each sliding window is obtained. The polarimetric index sequence for each MTSI interference pulse is calculated sequentially using the same method.

[0030] The polarizability index within each sliding window is calculated using the following formula: (5); in ,when This corresponds to a completely nonpolarized wave. Corresponding to fully polarized waves; , , , These are the four components of the Stokes vector; the Stokes vector is represented as: (6); in and These represent the echo data received by the H-polarized channel and the V-polarized channel respectively within the sliding window; the superscript * indicates complex conjugate. and These represent taking the real part and the imaginary part, respectively.

[0031] Step 6: Based on the polarization index sequence of the pulses containing MTSI interference, locate the region where the MTSI interference is located in each pulse containing MTSI interference using an adaptive threshold.

[0032] Adaptive threshold It can be represented as: (7); in and These represent the mean and variance of the polarization indices for all interference-free pulses in the echo matrix block containing MTSI interference, respectively.

[0033] For each pulse containing MTSI interference, its polarization index sequence is compared with an adaptive threshold. The comparison is made by placing polarizability indices below this adaptive threshold. The positions of all sliding windows are determined as the area where MTSI interference is located, i.e., their distance-direction positions.

[0034] This is because the transmitted signals of spaceborne SAR systems are typically highly polarimetric coherent signals. After being scattered by ground objects, the polarimetric degree of the SAR echo is often lower than that of the transmitted signal. When a highly polarized RFI (Radio Frequency Irradiation) is superimposed on the target echo signal, the polarimetric degree of the interfering signal usually approaches 1. However, unlike most RFIs, the MTSI (Mediated Trace Indicator Signal) is essentially also a SAR echo signal scattered by ground objects. Therefore, when the target echo signal and the MTSI overlap, the polarimetric degree will actually decrease further.

[0035] Step 7: Update the initial interference mask based on the localization results of all MTSI interferences to obtain the final temporal interference mask and complete the interference detection.

[0036] For the initial interference mask For each row containing MTSI interference pulses, the values ​​of the MTSI interference region in that row are kept unchanged at 1, while the values ​​of the non-MTSI interference regions are set to 0, thus obtaining the final temporal interference mask. . The location of 1 is the location of the MTSI interference in the echo matrix block containing MTSI interference.

[0037] Example: In one embodiment of the present invention, the echo matrix of the cross-polarization channel and the echo matrix of the same-polarization channel are respectively divided into Each echo matrix is ​​divided into blocks; total number of azimuth sampling points Distance to total number of sampling points .

[0038] Figure 2 (a) and (b) are the incoherent accumulation results of the same block containing the MTSI interference echo matrix in VH and VV polarization modes, respectively. Figure 2 (c) and (d) represent the incoherent accumulation results of the same interference-free echo matrix block under VH and VV polarization modes. In this embodiment, the initial interference mask for a certain MTSI interference echo matrix block is as follows: Figure 3 As shown.

[0039] In this embodiment, when calculating the polarization index sequence containing MTSI interference pulses, the sliding window length is 1969 and the sliding step size is 100.

[0040] Figure 4 This represents the range-oriented localization results for interference pulses containing MTSI interference, where... Figure 4 (a) and (c) show the localization results of MTSI interference in pulse one and pulse two, respectively. Figure 4(b) and (d) are their corresponding time-frequency spectra, showing that the interference localization results basically match the distance cells covered by the interference in the time-frequency spectra. The final time-domain interference mask generated after interference detection in this embodiment is shown below. Figure 5 As shown.

[0041] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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. Such 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 this application, and should all be included within the protection scope of this application.

Claims

1. A method for detecting interstellar scattering interference based on polarization characteristics, characterized in that, include: The echo matrix of the cross-polarization channel and the echo matrix of the same polarization channel of the spaceborne SAR in dual polarization mode are synchronously divided into multiple echo matrix blocks along the azimuth direction. For each echo matrix block of the cross-polarization channel and the co-polarization channel, the echo data are incoherently accumulated along the range direction; the corresponding relative entropy is calculated based on the incoherent accumulation results, and the echo matrix block containing MTSI interference is determined using the relative entropy; For each echo matrix block containing MTSI interference, calculate the energy of each pulse contained therein; For all pulses in the echo matrix block containing MTSI interference, cluster them according to their energy to filter out pulses containing MTSI interference and generate an initial interference mask; For each pulse containing MTSI interference, its polarizability index is calculated sequentially using a sliding window to construct a polarizability index sequence; Based on the polarimetric index sequence of pulses containing MTSI interference, the region where MTSI interference is located in each pulse containing MTSI interference is located using an adaptive threshold. Based on the location results of all MTSI interferences, the initial interference mask is updated to obtain the final temporal interference mask, thus completing the interference detection.

2. The inter-satellite scattering interference detection method based on polarization characteristics according to claim 1, characterized in that, The relative entropy is calculated based on the incoherent accumulation results, including: ； in, This indicates the first term of the cross-polarization channel and the co-polarization channel. Each echo matrix is ​​divided into blocks. , The relative entropy, and They represent , The result of incoherent accumulation along the distance, i Represents the azimuth sampling point number. , This indicates rounding down. This indicates the total number of sampling points in the azimuth direction. This represents the number of echo matrix blocks divided into cross-polarization channels and co-polarization channels.

3. The inter-satellite scattering interference detection method based on polarization characteristics according to claim 1, characterized in that, Determining echo matrix blocks containing MTSI interference using relative entropy includes: Set an entropy threshold; when the cross-polarized channel and the same-polarized channel... Each echo matrix is ​​divided into blocks. , When the relative entropy is greater than the entropy threshold, it indicates that... or MTSI interference echoes are present; then, calculations are performed separately. , The variance of all incoherent cumulative results is calculated; the two variances are compared, and the echo matrix block corresponding to the larger variance is determined as the echo matrix block containing MTSI interference.

4. The inter-satellite scattering interference detection method based on polarization characteristics according to claim 1, characterized in that, For all pulses in the echo matrix block containing MTSI interference, cluster them according to their energy to filter out pulses containing MTSI interference, and generate an initial interference mask, including: The K-means clustering algorithm is used to cluster the energy of all pulses to obtain multiple clusters. The mean energy of the center of all clusters is calculated. Then, for each cluster, if the energy of the center of the cluster is higher than the mean, the cluster is regarded as a cluster containing MTSI interference, and all pulses contained therein are MTSI interference pulses. The remaining clusters are interference-free pulse clusters, and all pulses contained therein are interference-free pulses. Finally, for the echo matrix containing MTSI interference, the data in the row containing MTSI interference pulses is set to 1, and the data in the row without interference pulses is set to 0, thus obtaining the initial interference mask.

5. The inter-satellite scattering interference detection method based on polarization characteristics according to claim 1, characterized in that, For each pulse containing MTSI interference, its polarizability index is calculated sequentially using a sliding window, constructing a polarizability index sequence, including: Set the length and sliding step of the sliding window; starting from the beginning position of the MTSI interference pulse, calculate the polarimetric index of the echo data contained in each sliding window; after the sliding window reaches the end of the MTSI interference pulse according to the sliding step, the polarimetric index sequence composed of the polarimetric indexes calculated for each sliding window can be obtained.

6. The inter-satellite scattering interference detection method based on polarization characteristics according to claim 1, characterized in that, The formula for calculating the polarization index within each sliding window is as follows: ； in ,when This corresponds to a completely nonpolarized wave. Corresponding to fully polarized waves; , , , These are the four components of the Stokes vector.

7. The inter-satellite scattering interference detection method based on polarization characteristics according to claim 1, characterized in that, Based on the polarimetric index sequence of pulses containing MTSI interference, the region containing MTSI interference in each pulse is located using an adaptive threshold, including: Adaptive threshold Represented as: ;in and These represent the mean and variance of the polarization indices for all interference-free pulses in the echo matrix block containing MTSI interference, respectively. For each pulse containing MTSI interference, its polarization index sequence is compared with an adaptive threshold. The comparison is made by placing polarizability indices below this adaptive threshold. The positions of all sliding windows are determined to be the areas where MTSI interference occurs.

8. The inter-satellite scattering interference detection method based on polarization characteristics according to claim 1, characterized in that, Based on the localization results of all MTSI interferences, the initial interference mask is updated to obtain the final temporal interference mask, including: For each row containing MTSI interference pulses in the initial interference mask, the non-MTSI interference regions in that row are set to 0, thus obtaining the final time-domain interference mask, where the position of 1 is the position of MTSI interference.

9. A terminal device, comprising a processor, a memory, and a computer program stored in the memory; characterized in that, When the processor executes a computer program, it implements the interstellar scattering interference detection method based on polarization characteristics as described in any one of claims 1-8.

10. A computer-readable storage medium storing a computer program; characterized in that, When the computer program is executed by the processor, it implements the interstellar scattering interference detection method based on polarization characteristics as described in any one of claims 1-8.

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