A method and device for suppressing in-band interference in DBF-SAR data mapping

Abstract

The present invention discloses a method and device for suppressing interference within a DBF-SAR data mapping band, and belongs to the technical field of digital beamforming synthetic aperture radar. The method comprises collecting interference-containing DBF-SAR echo data, and performing distance compression on the echo data of each channel in the elevation direction; performing sub-array division on the observation signal matrix of the SAR system, and synthesizing sub-array data based on SCORE weighting; pre-processing the synthesized sub-array data; solving the fourth-order cumulant matrix of the pre-processed sub-array data, and performing eigenvalue decomposition to obtain an estimated matrix of the unitary matrix; obtaining the separation result of the pre-processed sub-array data based on the estimated matrix; measuring the kurtosis of the separation result data to determine the SAR signal component, and performing amplitude correction; performing distance compression on the amplitude-corrected SAR signal component to obtain interference-free echo data. The present invention realizes effective suppression of interference within the mapping band while ensuring DBF performance.

Description

Technical Field

[0001] The invention belongs to the technical field of digital beamforming synthetic aperture radar, and in particular relates to a method and a device for suppressing in-band interference in DBF-SAR data mapping. Background Art

[0002] SAR can obtain high-precision, continuous coverage ground target information all day and all weather. It has been widely used in military reconnaissance, resource exploration, topographic mapping, environmental monitoring, disaster warning and assessment and other related fields, and has achieved a series of important results. Since SAR shares spectrum resources with electromagnetic equipment in the same frequency band, it is easy to receive co-frequency interference caused by other electromagnetic equipment. With the further development and utilization of the electromagnetic spectrum and the rapid development of modern radio technology, the interference suffered by SAR has become a key problem that needs to be urgently solved in the application of on-orbit satellites. On the one hand, such interference will affect SAR signal processing and image interpretation, and hinder the subsequent business application of SAR. On the other hand, with the reuse of spectrum resources and the upgrading of radio technology, the system, bandwidth and power of the interference signal will be far more complex than the traditional narrowband point-frequency interference, and some interference suppression methods based on time domain, frequency domain, time-frequency domain and transform domain will no longer be applicable.

[0003] The DBF-SAR system has spatial freedom, which provides a new dimension and scope for interference suppression. Through multi-channel reception and beamforming technology, DBF-SAR can suppress interference without losing SAR signals, providing a new direction for the next generation of spaceborne SAR to counter interference. On the one hand, taking the Scan on Receive (SCORE) mode of the elevation multi-channel system as an example, this mode uses a wide beam to cover a wide swath during transmission; during reception, the system forms a high-gain digital receiving beam in real time along the time-varying arrival direction of the echo, and scans the wide swath in a fast time. At this time, the echo scanned by the SCORE beam can be regarded as a coherently superimposed SAR backscatter signal and an incoherently superimposed interference signal. The signal is enhanced and the interference is suppressed to a certain extent. In addition, the DBF-SAR system can combine spatial filtering technology to digitally control the zero point of the directional pattern in post-processing to point it in the direction of the interference, thereby suppressing the interference. Between 2015 and 2019, Bollian et al. verified the effectiveness of DBF-SAR in suppressing interference based on the Minimum Variance Distortionless Response (MVDR) beamformer. Sidelobe Canceller (SLC) is a special spatial filter that can effectively suppress active sidelobe interference and has been widely used in phased array radar systems. SLC assumes that the main lobe of the radar antenna is narrow, the gain is high, and the directivity is strong, while the side lobe of the antenna is wide, the gain is low, and interference can easily enter through the side lobe. SLC requires an additional auxiliary antenna and uses the LMS or maximum SNR criteria to control the phase and amplitude weighting of the auxiliary antenna to coherently subtract the interference received by the main channel.

[0004] For DBF-SAR, the anti-interference performance of the SCORE mode is limited by the signal-to-interference-to-noise ratio. When the interference energy is significant, the interference suppression performance of this method is seriously affected. The traditional SLC method can only eliminate sidelobe interference and requires additional auxiliary antennas to meet performance requirements, which not only increases the complexity of the system, but also consumes additional on-board resources. Importantly, when the interference source is located within the mapping band, the interference and the SAR echo's wave direction will arrive at the receiver at the same time, and the beamforming technology will cause the main lobe of the receiving pattern to be distorted, further affecting the SAR signal impulse response. Therefore, there is no effective solution to the problem of main lobe interference within the mapping band in DBF-SAR systems. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method and device for suppressing interference within the DBF-SAR data mapping band. Subarray synthesis is first adopted, and then interference suppression is performed. Interference suppression within the mapping band is achieved while ensuring DBF performance, and the tolerance to SINR is higher.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A DBF-SAR data mapping in-band interference suppression method, comprising:

[0008] Step 1: Collect the DBF-SAR echo data containing interference, and perform distance compression on the echo data of each channel in the elevation direction;

[0009] Step 2: Divide the observation signal matrix of the SAR system into sub-arrays, and synthesize the sub-array data based on SCORE weights;

[0010] Step 3: preprocessing the synthesized sub-array data, wherein the preprocessing includes removing the mean and whitening processing;

[0011] Step 4, solving the fourth-order cumulant matrix of the preprocessed sub-array data, and performing eigenvalue decomposition on the fourth-order cumulant matrix to obtain an estimated matrix of the unitary matrix;

[0012] Step 5: Based on the estimated matrix, obtain the separation result of the preprocessed sub-array data;

[0013] Step 6, measuring the kurtosis of the separation result data to determine the SAR signal component, and performing amplitude correction;

[0014] Step 7: Decompress the amplitude-corrected SAR signal component to obtain interference-free echo data.

[0015] On the other hand, the present invention also provides a DBF-SAR data mapping in-band interference suppression device, comprising:

[0016] The data acquisition and processing unit is used to acquire the DBF-SAR echo data containing interference, and perform distance compression on the echo data of each channel in the elevation direction; divide the observation signal matrix of the SAR system into sub-arrays, and synthesize the sub-array data based on SCORE weighting; and pre-process the synthesized sub-array data, wherein the pre-processing includes de-averaging and whitening processing;

[0017] A calculation unit is used to solve the fourth-order cumulant matrix of the preprocessed sub-array data, and perform eigenvalue decomposition on the fourth-order cumulant matrix to obtain an estimated matrix of the unitary matrix; based on the estimated matrix, obtain the separation result of the preprocessed sub-array data; measure the kurtosis of the separation result data to determine the SAR signal component, and perform amplitude correction;

[0018] The echo acquisition unit is used to decompress the amplitude-corrected SAR signal component and acquire interference-free echo data.

[0019] In a third aspect, the present invention provides an electronic device, comprising: one or more processors; a memory for storing one or more programs; wherein, when the one or more programs are executed by the one or more processors, the one or more processors implement the aforementioned DBF-SAR data mapping in-band interference suppression method.

[0020] In a fourth aspect, the present invention provides a computer-readable storage medium having executable instructions stored thereon, which, when executed by a processor, enables the processor to implement the aforementioned method for suppressing in-band interference in DBF-SAR data mapping.

[0021] The beneficial effects of the present invention are:

[0022] Aiming at the problem of main lobe distortion of the receiving pattern caused by spatial domain filtering methods when suppressing interference within the mapping band, the present invention first divides the subarray for SCORE processing. The SCORE beam can enhance the echo gain for each mapping band. At this time, the receiving pattern corresponding to each range unit only considers enhancing the echo in that direction, so there will be no pattern distortion problem.

[0023] The present invention models the interfered channel data as a linear mixed model, that is, the received channel data is a linear combination of the observation matrix and the mixing matrix, so the SAR signal component and the interference signal component in each observation data can be separated by estimating the mixing matrix;

[0024] Since the estimated unmixing matrix has ordering uncertainty, the present invention introduces the kurtosis coefficient to measure the Gaussianity of the separation result based on the statistical characteristics of the SAR echo data, thereby realizing the screening of the SAR echo signal and the interference signal from the separation result. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A flow chart of a method for suppressing in-band interference in DBF-SAR data mapping according to the present invention;

[0026] Figure 2 This is the SAR echo data diagram containing interference;

[0027] Figure 3 This is the SAR echo data diagram after interference suppression;

[0028] Figure 4 This is the SAR data imaging result after interference suppression;

[0029] Figure 5 This is a slice analysis diagram of the point target in range and azimuth. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0031] like Figure 1 FIG. 1 is a flow chart of a method for suppressing in-band interference in DBF-SAR data mapping according to the present invention, the method comprising:

[0032] Step 1: Collect DBF-SAR echo data containing interference and perform range compression on the echo data of each channel in the elevation direction.

[0033] Specifically, the data of each elevation channel is set to be composed of SAR echo signals With N interference signals , they can be expressed as:

[0034] (1)

[0035] In the formula, S represents the echo data of each channel, Indicates the distance to fast time, the matched filter used for distance compression is , is the frequency modulation, j represents the imaginary unit, Represents the distance frequency; the echo data S of each channel is distance compressed, which is expressed as:

[0036] (2)

[0037] in, and Here, range compression has two functions. On the one hand, this process can alleviate the problem of pulse extension loss in DBF synthesis. On the other hand, the matched filter used in range compression will be mismatched with the interference signal, making the interference and echo different in statistical characteristics.

[0038] Step 2: Divide the observation signal matrix of the SAR system into sub-arrays and synthesize the sub-array data based on SCORE weights.

[0039] Specifically, assume that the SAR system has M receiving channels, then the observed signal matrix It is expressed as: ;

[0040] Among them, R, A, and O are the observation signal matrix, mixing matrix, and noise matrix respectively, and the corresponding vectors are expressed as:

[0041] (3)

[0042] in, is the steering vector of the corresponding signal, where is the direction of the echo, arrive Indicates the directions of the N interference signals. Assuming that the SAR system receives interference signals from N directions, it needs to be divided into N+1 sub-arrays, and the nth sub-array is:

[0043] (4)

[0044] The corresponding SCORE weighted value is expressed as:

[0045] (5)

[0046] in, is the carrier frequency, is the antenna installation angle, c is the speed of light, is the antenna spacing, is the array element spacing, When the SAR antenna receives the echo, The lower viewing angle corresponding to the pulse center at the moment is expressed as:

[0047] (6)

[0048] Where H is the height of the radar from the ground, is the radius of the Earth, The target slant distance corresponding to the received echo at that moment. With subarray data Multiply them together to get the weighted synthesized sub-array data:

[0049] (7)

[0050] Step 3: Preprocessing the synthesized sub-array data, including de-averaging and whitening.

[0051] Specifically, the mean removal is expressed as:

[0052] (8)

[0053] in, is the sub-array data after removing the mean, For the sake of expectation.

[0054] Whitening can eliminate the correlation between observed signals, thereby simplifying the extraction process of independent components and improving the convergence of the algorithm. The autocorrelation matrix is ​​subjected to eigenvalue decomposition and expressed as:

[0055] (9)

[0056] in, is the eigenvalue of the autocorrelation matrix, is the eigenvector of the autocorrelation matrix, with the superscript represents the conjugate transpose, express The autocorrelation matrix of . Whitening matrix It can be expressed as:

[0057] (10)

[0058] The whitening process can be expressed as:

[0059] (11)

[0060] in, is the sub-array data after whitening. Define a unitary matrix as the whitening matrix and the mixing matrix The product of According to formula (11), in order to obtain the observation matrix , then we need to estimate the unitary matrix.

[0061] Step 4: Solve the fourth-order cumulant matrix of the preprocessed sub-array data, and perform eigenvalue decomposition on the fourth-order cumulant matrix to obtain an estimated matrix of the unitary matrix.

[0062] Specifically, define the whitened sub-array data The fourth-order cumulant matrix , whose (i,j)th element is defined as:

[0063] (12)

[0064] in, is the cumulative amount, = is an arbitrary non-zero matrix, i and For the matrix The row and column subscripts of the elements in; for Elements in a matrix; is the vector representation of the whitened sub-array data, yes The conjugate of represents conjugate; m and l are the row and column subscripts of the elements in the matrix respectively; since the fourth-order cumulant has the characteristics of multilinearity, it can be expressed as:

[0065] (13)

[0066] in, for The fourth-order cumulant of , s is the observation matrix, that is, the vectorized representation of SAR echo data, is a unitary matrix No. List, represents a diagonal matrix.

[0067] For the fourth-order cumulant matrix Perform eigenvalue decomposition and obtain the unitary matrix The estimation matrix .

[0068] Step 5: Based on the estimated matrix, obtain the separation results of the preprocessed sub-array data.

[0069] Specifically, according to the properties of the unitary matrix, the separation result of the sub-array data after whitening is obtained, which is expressed as:

[0070] (14)

[0071] in, represents the estimation matrix of the unitary matrix; represents the whitening matrix obtained by formula 10; is the synthesized sub-array data after weighted synthesis.

[0072] Step 6: Measure the kurtosis of the separated result data to determine the SAR signal component and perform amplitude correction.

[0073] Specifically, since the estimated matrix of the unitary matrix With ordering uncertainty, the results need to be separated from the subarray data Based on the prior knowledge that SAR echo data obeys Gaussian distribution, the kurtosis value is introduced to measure The Gaussianity of each signal in the , the kurtosis value is defined as:

[0074] (15)

[0075] in, For separation results A line of signal, and is its mean and variance. Since the kurtosis value of a signal that follows a Gaussian distribution is approximately 3, the separation result The signal with a kurtosis close to 3 is judged as non-interfering SAR echo data. The signal with a kurtosis close to 3 is the SAR echo data s, and amplitude correction is performed on s.

[0076] Step 7: Decompress the amplitude-corrected SAR signal components to obtain interference-free echo data.

[0077] Specifically, the matched filter used to solve the distance compression is . For non-interference SAR echo data Decompress the range to obtain the final SAR echo data after interference suppression , expressed as:

[0078] (16)

[0079] Example:

[0080] Interference suppression tests were carried out on simulated airborne SAR data with pulsed RF interference added to verify the effectiveness of the technical solution of the present invention, where the interference source was located within the surveying band. Figure 2 This is the SAR original echo amplitude image with pulsed RF interference added. The white bright bar is the pulsed RF interference. Due to the strong interference energy, it drowns the SAR echo. Figure 3 This is the SAR echo amplitude image after being processed by the proposed scheme. The pulse interference is obviously eliminated. Figure 4 This is the SAR data imaging result after interference suppression. It can be clearly seen that there are five strong point targets set in the simulation; Figure 5 The range and azimuth slice analysis diagrams of the scene center point are shown in the first row, where the one-dimensional slice diagram of the point target and the second and third rows are the one-dimensional phase diagrams of the point target. Figure 5 It can be seen that this method can effectively suppress the interference within the mapping band in DBF-SAR data.

[0081] On the other hand, the present invention also provides a DBF-SAR data mapping in-band interference suppression device, which includes various modules capable of implementing various steps of the aforementioned method, specifically including:

[0082] The data acquisition and processing unit is used to acquire the DBF-SAR echo data containing interference, and perform distance compression on the echo data of each channel in the elevation direction; divide the observation signal matrix of the SAR system into sub-arrays, and synthesize the sub-array data based on SCORE weighting; and pre-process the synthesized sub-array data, wherein the pre-processing includes de-averaging and whitening processing;

[0083] A calculation unit is used to solve the fourth-order cumulant matrix of the preprocessed sub-array data, and perform eigenvalue decomposition on the fourth-order cumulant matrix to obtain an estimated matrix of the unitary matrix; based on the estimated matrix, obtain the separation result of the preprocessed sub-array data; measure the kurtosis of the separation result data to determine the SAR signal component, and perform amplitude correction;

[0084] The echo acquisition unit is used to decompress the amplitude-corrected SAR signal component and acquire interference-free echo data.

[0085] In a third aspect, the present invention provides an electronic device, comprising: one or more processors; a memory for storing one or more programs; wherein, when the one or more programs are executed by the one or more processors, the one or more processors implement the aforementioned DBF-SAR data mapping in-band interference suppression method.

[0086] In a fourth aspect, the present invention provides a computer-readable storage medium having executable instructions stored thereon, which, when executed by a processor, enables the processor to implement the aforementioned method for suppressing in-band interference in DBF-SAR data mapping.

[0087] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for suppressing in-band interference in DBF-SAR data mapping, characterized in that: The method comprises: Step 1: Collect the DBF-SAR echo data containing interference, and perform distance compression on the echo data of each channel in the elevation direction; Step 2: Divide the observation signal matrix of the SAR system into sub-arrays, and synthesize the sub-array data based on SCORE weights; Step 3: preprocessing the synthesized sub-array data, wherein the preprocessing includes removing the mean and whitening processing; Step 4, solving the fourth-order cumulant matrix of the preprocessed sub-array data, and performing eigenvalue decomposition on the fourth-order cumulant matrix to obtain an estimated matrix of the unitary matrix; Step 5: Based on the estimated matrix, obtain the separation result of the preprocessed sub-array data; Step 6, measuring the kurtosis of the separation result data to determine the SAR signal component, and performing amplitude correction; Step 7: Decompress the amplitude-corrected SAR signal component to obtain interference-free echo data.

2. The method for suppressing in-band interference in DBF-SAR data mapping according to claim 1, characterized in that: The step 1 includes setting the data of each elevation channel to be composed of a SAR echo signal. With N interference signals constitute: （1） In the formula, S represents the echo data of each channel, Indicates the distance to fast time, the matched filter used for distance compression is , To adjust the frequency, represents the imaginary unit, Indicates the distance frequency; perform distance compression on the echo data S of each channel: （2） in, and They are the forward and inverse Fourier transform respectively.

3. The method for suppressing in-band interference in DBF-SAR data mapping according to claim 2, characterized in that: The step 2 comprises: Set M receiving channels of the SAR system and obtain the observation signal matrix; Assume that the SAR system receives N interference signals and needs to be divided into N+1 sub-arrays, and the data of each sub-array and the corresponding SCORE weighted value are calculated; The sub-array data and the corresponding SCORE weighted value are multiplied to obtain the weighted synthesized sub-array data.

4. The method for suppressing in-band interference in DBF-SAR data mapping according to claim 3, characterized in that: The step 3 comprises: Subtracting the mean of the weighted synthesized sub-array data from the weighted synthesized sub-array data to obtain the sub-array data after removing the mean; The autocorrelation matrix of the sub-array data after the mean value is removed is calculated and the eigenvalue decomposition is performed to obtain the whitening matrix. The sub-array data after the mean value is removed is processed based on the whitening matrix to obtain the whitened sub-array data.

5. The method for suppressing in-band interference in DBF-SAR data mapping according to claim 4, characterized in that: The step 5 comprises: Define the unitary matrix as the product of the whitening matrix and the mixing matrix; According to the properties of the unitary matrix, the separation results of the whitened sub-array data are obtained.

6. The method for suppressing in-band interference in DBF-SAR data mapping according to claim 5, characterized in that: The step 6 comprises: Based on the fact that SAR echo data follows Gaussian distribution, the kurtosis value is introduced to measure the Gaussianity of each signal in the separation result data. The interference-free SAR echo data in the result data is screened and separated based on the kurtosis value and amplitude correction is performed.

7. The method for suppressing in-band interference in DBF-SAR data mapping according to claim 6, characterized in that: In step 7, the matched filter The interference-free SAR echo data after amplitude correction is decompressed to obtain the final interference-suppressed SAR echo data.

8. A DBF-SAR data mapping in-band interference suppression device, characterized in that: include: The data acquisition and processing unit is used to collect the DBF-SAR echo data containing interference and perform distance compression on the echo data of each channel in the elevation direction; The observation signal matrix of the SAR system is divided into sub-arrays, and sub-array data is synthesized based on SCORE weighting; the synthesized sub-array data is pre-processed, and the pre-processing includes de-averaging and whitening processing; A calculation unit, used for solving the fourth-order cumulant matrix of the preprocessed sub-array data, and performing eigenvalue decomposition on the fourth-order cumulant matrix to obtain an estimated matrix of the unitary matrix; Based on the estimated matrix, the separation result of the preprocessed sub-array data is obtained; The kurtosis of the separated result data is measured to determine the SAR signal component and perform amplitude correction; The echo acquisition unit is used to decompress the amplitude-corrected SAR signal component and acquire interference-free echo data.

9. An electronic device, characterized in that: include: one or more processors; A memory for storing one or more programs; Wherein, when one or more programs are executed by the one or more processors, the one or more processors implement the DBF-SAR data mapping in-band interference suppression method as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that: Executable instructions are stored thereon, and when the instructions are executed by a processor, the processor can implement a method for suppressing in-band interference in DBF-SAR data mapping as described in any one of claims 1 to 7.

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