CN-122017844-A - SAR image LFM interference suppression method based on phase gradient estimation and SPECAN filtering

CN122017844ACN 122017844 ACN122017844 ACN 122017844ACN-122017844-A

Abstract

The invention provides an SAR image LFM interference suppression method based on phase gradient estimation and SPECAN filtering, which comprises the steps of dividing a single-view complex SAR image into a plurality of image blocks, estimating the distance direction frequency modulation rate of each image block by adopting a multi-stage phase gradient method, transposing the image blocks, estimating the azimuth direction frequency modulation rate by adopting a multi-stage phase gradient method, carrying out SPECAN filtering processing on each image block to restore an original phase, and splicing all the image blocks subjected to the SPECAN filtering processing to obtain a complete SAR image subjected to interference suppression. The invention innovatively introduces a multi-stage phase gradient method, and can rapidly and accurately estimate the frequency modulation of the LFM interference without global search through iteration from small step size to large step size and a multi-stage phase unwrapping mechanism.

Inventors

YANG HUIZHANG
Cai Jinmeng
Yang Heao
Fu Menghao
YANG XUE
LI XINYUAN

Assignees

南京理工大学

Dates

Publication Date: 20260512
Application Date: 20260414

Claims (10)

1. The SAR image LFM interference suppression method based on phase gradient estimation and SPECAN filtering is characterized by comprising the following steps of: step 1, dividing a single-view complex SAR image into a plurality of image blocks; Step 2, estimating the distance frequency modulation rate of each image block by adopting a multi-stage phase gradient method; Step 3, transposing the image blocks, and estimating azimuth tuning frequency by adopting a multistage phase gradient method; step 4, SPECAN filter processing is carried out on each image block, and the original phase is recovered; and 5, splicing all the SPECAN filtered image blocks to obtain a complete SAR image after interference suppression.
2. The SAR image LFM interference suppression method based on phase gradient estimation and SPECAN filtering of claim 1, wherein the specific method for estimating the distance-wise frequency of each image block by using a multistage phase gradient method is as follows: step 2.1, carrying out amplitude normalization on the image block data to obtain normalized data, setting a target delay step length, and initializing iteration times And iteration step ; Step 2.2 in the first step In the iteration, the current step length is utilized Calculating a first-order differential matrix and a second-order differential matrix; step 2.3 summing the second order differential matrix to suppress noise and extracting the winding phase ; Step 2.4, multi-stage phase unwrapping and frequency modulation rate updating: If it is Calculate the first from the winding phase Frequency estimation value is adjusted for a plurality of iterations: ; If it is Frequency estimation value is adjusted by using the previous iteration Unwinding to obtain the number of unwound blunts ; According to the number of unwind blurs Calculate the first Frequency estimation value is adjusted for a plurality of iterations: ; ; In the formula, Is the true phase; the updated frequency is adjusted; step 2.5, updating the next delay step in proportion; Step 2.6 repeating steps 2.2 to 2.5 until Will be at the first The frequency modulation rate estimate for the next iteration is taken as the distance-wise frequency modulation.
3. The SAR image LFM interference suppression method based on phase gradient estimation and SPECAN filtering of claim 2, wherein the current step size is utilized Calculating a first-order and second-order differential matrix: ; ; In the formula, And Respectively the first First and second order differential matrices of the secondary iterations; representing the Hadamard product; Representing complex conjugate operations; And Indicating the step length For normalized matrix Right and left sub-matrices acquired by slicing in the distance direction, And Indicating the step length For first order differential matrix Right and left sub-matrices acquired by slicing in the distance direction.
4. The SAR image LFM interference suppression method based on phase gradient estimation and SPECAN filtering of claim 2, wherein the unwrapped blur number The method comprises the following steps: 。
5. The SAR image LFM interference suppression method based on phase gradient estimation and SPECAN filtering of claim 2, wherein the specific formula for updating the next delay step in proportion is: 。
6. the SAR image LFM interference suppression method based on phase gradient estimation and SPECAN filtering of claim 2, wherein the set target delay step is specifically: ; In the formula, The number of points is sampled for the distance direction.
7. The SAR image LFM interference suppression method based on phase gradient estimation and SPECAN filtering of claim 1, wherein the specific method for recovering the original phase by performing SPECAN filtering processing on each image block is as follows: Frequency modulation based on estimated range And azimuth frequency modulation rate Constructing a two-dimensional complex deskewing function; Image block data Multiplying the time domain declivity function to finish time domain declivity; Performing two-dimensional FFT and zero frequency translation operation on the complex data matrix subjected to two-dimensional declining, and converting the complex data matrix into a two-dimensional frequency domain; Adopting a constant false alarm rate algorithm to perform self-adaptive strong interference point detection in a two-dimensional frequency domain; and carrying out two-dimensional inverse FFT on the frequency spectrum matrix subjected to the notch processing to restore to a time domain, and multiplying the time domain by a conjugate declivity function to restore the original phase.
8. The SAR image LFM interference suppression method based on phase gradient estimation and SPECAN filtering of claim 7, wherein the constructed two-dimensional complex deskewing function: ; In the formula, And Time coordinates representing the azimuth direction and the distance direction respectively; is a two-dimensional complex declivity reference function.
9. The SAR image LFM interference suppression method based on phase gradient estimation and SPECAN filtering according to claim 7, wherein the specific method for self-adapting strong interference point detection in a two-dimensional frequency domain by adopting a constant false alarm rate algorithm is as follows: A sliding window is adopted in the two-dimensional frequency spectrum, and the amplitude value of the adjacent frequency point in the surrounding reference window is calculated by taking the current frequency point to be measured as the center; Dynamic calculation of adaptive threshold corresponding to frequency point to be measured by combining amplitude values of adjacent frequency points The method specifically comprises the following steps: ; In the formula, As a threshold factor of the number of times, The average value of the amplitude values of the pixel points in the reference window around the frequency point to be detected is obtained; the frequency spectrum amplitude of the frequency point to be measured And comparing the self-adaptive threshold corresponding to the frequency point to be detected, namely judging that the strong interference condition is met if the frequency spectrum amplitude of the frequency point to be detected is larger than the self-adaptive threshold, forcibly setting the value of the frequency point to be detected in the frequency spectrum to zero, and reserving the frequency spectrum amplitude of the frequency point to be detected if the frequency spectrum amplitude of the frequency point to be detected is smaller than or equal to the self-adaptive threshold.
10. The SAR image LFM interference suppression method based on phase gradient estimation and SPECAN filtering of claim 9, wherein the threshold factor is specifically: ; In the formula, Is the preset false alarm probability of the traffic signal, Is the total number of pixels within the reference window.

Description

SAR image LFM interference suppression method based on phase gradient estimation and SPECAN filtering Technical Field The invention belongs to the technical field of radar data processing, and particularly relates to a SAR image LFM interference suppression method based on phase gradient estimation and SPECAN (spectral analysis) filtering. Background Synthetic aperture radar is a core sensor for remote sensing observation. However, the SAR system is very susceptible to interference of chirp signals from radiation sources such as ground radars in a complex electromagnetic environment, so that a large-area haze or stripes appear on an image, and a real ground object target is seriously covered. The existing interference suppression method is mainly divided into pretreatment and post-treatment. In the post-processing method, block Subspace Filtering (BSF) and an improved algorithm thereof separate interference through matrix decomposition, but the problems of high computational complexity, sensitivity to strong scattering points and the like exist, the notch filtering is simple but can damage signals, and the time-frequency analysis method has large calculated amount and cross-term interference. In recent years, a SPECAN filtering method based on frequency modulation rate estimation is proposed, but in the traditional method, the frequency modulation rate estimation depends on priori knowledge or adopts a search method to cause low calculation efficiency, so that the actual engineering requirements are difficult to meet. Disclosure of Invention The invention provides a SAR image LFM interference suppression method based on phase gradient estimation and SPECAN filtering, and aims to solve the problems of high computational complexity, low frequency modulation rate estimation efficiency, easiness in causing effective signal damage and the like in the existing single-view complex SAR image LFM interference suppression method. The technical scheme for realizing the purpose of the invention is that the SAR image LFM interference suppression method based on phase gradient estimation and SPECAN filtering comprises the following steps: step 1, dividing a single-view complex SAR image into a plurality of image blocks; Step 2, estimating the distance frequency modulation rate of each image block by adopting a multi-stage phase gradient method; Step 3, transposing the image blocks, and estimating azimuth tuning frequency by adopting a multistage phase gradient method; step 4, SPECAN filter processing is carried out on each image block, and the original phase is recovered; and 5, splicing all the SPECAN filtered image blocks to obtain a complete SAR image after interference suppression. Compared with the prior art, the invention has the remarkable advantages that: 1. The invention innovatively introduces a multistage phase gradient method, and can rapidly and accurately estimate the frequency modulation of the LFM interference without global search through iteration from small step length to large step length and a multistage phase unwrapping mechanism. This not only avoids the phase ambiguity problem easily caused by long delay step length, but also greatly reduces the calculation complexity of the algorithm. 2. The invention utilizes the frequency modulation rate of accurate estimation to construct the declivity function, the LFM interference of the broadband is perfectly compressed into extremely narrow bright spots in the frequency domain, the extremely narrow notch processing is carried out at the moment, and the conjugate phase compensation of the inverse Fourier transform and the declivity function is matched, so that the original amplitude and phase information of SAR images can be reserved to the maximum extent while the interference is thoroughly removed, and the image information loss is small. 3. The method has wider scene adaptation range and strong generalization capability, realizes local accurate estimation of non-uniformly distributed interference through image blocking processing, eliminates block boundary effect through overlapping region design, provides clear parameter adjustment rules for phase ambiguity scenes caused by strong interference, can adapt SAR images with different resolutions, different sizes and different interference intensities, and can realize stable inhibition effect no matter single-point strong interference or distributed broadband interference. The present invention will be described in further detail with reference to the accompanying drawings. Drawings FIG. 1 is a flow chart of the present invention. Fig. 2 is a detailed flow chart of a multistage phase gradient method. Fig. 3 is an effect diagram before processing SAR image data according to the present invention. Fig. 4 is an effect diagram of the present invention after processing SAR image data. Detailed Description A SAR image LFM interference suppression method based on phase gradient estimation and SPECAN filtering is us