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CN-121995379-A - ISAR distance envelope alignment method and system based on phase difference

CN121995379ACN 121995379 ACN121995379 ACN 121995379ACN-121995379-A

Abstract

The invention discloses an ISAR distance envelope alignment method and system based on phase difference, and belongs to the technical field of radars. The method comprises the steps of estimating echo signals after pulse compression sample by sample and compensating average phase change of adjacent samples, dividing a pair of azimuth signals in a distance frequency domain, adding rectangular windows respectively with zero frequency as a limit, generating an upper sideband signal and a lower sideband signal by sampling each azimuth, carrying out conjugate multiplication on four signals of the adjacent samples for three times to obtain differential signals, obtaining adjacent offset by maximum likelihood estimation through the differential signals, aligning adjacent envelopes according to estimation results, accumulating the aligned envelopes, repeating the steps with the next sample, and finally completing envelope alignment of all samples. The invention can realize the distance envelope alignment precision of the sub-pixel level without up-sampling and interpolation operation, and effectively avoids the problem of the opposite echo caused by amplitude modulation in the traditional amplitude dependent algorithm.

Inventors

  • ZHANG HENG
  • SHI SHUO
  • DENG YUNKAI
  • XUE FENGLI
  • ZHANG LEI

Assignees

  • 中国科学院空天信息创新研究院

Dates

Publication Date
20260508
Application Date
20260323

Claims (10)

  1. 1. An ISAR distance envelope alignment method based on phase difference, the method comprising: step 1, carrying out adjacent sampling average phase compensation processing on echo signals after pulse compression to obtain compensated signals; step 2, performing block processing on the compensated signal in a distance frequency domain, and sampling each azimuth to generate an upper sideband signal and a lower sideband signal; step 3, performing conjugate multiplication processing on four signals of two adjacent samples to obtain a differential signal; step 4, obtaining envelope offset estimated values of adjacent samples by using the differential signals through maximum likelihood estimation; step 5, aligning adjacent samples according to the envelope offset estimation value to obtain aligned signals; and 6, accumulating the aligned signals, and repeating the steps 1-5 with the accumulated result and the next sample for recursively aligning until the envelope alignment of all the samples is completed.
  2. 2. The ISAR distance envelope alignment method based on phase difference according to claim 1, wherein in the step 1, an average phase change factor of adjacent samples is estimated, the average phase change factor is equal to a sum of trailing edge distances of conjugate multiplication of the adjacent samples and the previous samples, and divided by a modulus value, and phase compensation is performed on the adjacent samples by using the conjugate of the average phase change factor to obtain the compensated signal.
  3. 3. The ISAR distance envelope alignment method based on phase difference according to claim 1, wherein in the step 2, an upper sideband filter and a lower sideband filter are set, the two filters are both limited by zero frequency, window filtering is performed on distance-oriented frequency spectrums of the compensated signals respectively, and inverse fourier transformation is performed on the frequency spectrums after filtering respectively to obtain an upper sideband time domain signal and a lower sideband time domain signal.
  4. 4. The ISAR distance enveloping alignment method based on phase difference according to claim 1, wherein in the step 3, the conjugate of the upper sideband signal and the lower sideband signal of the adjacent next sample is multiplied, and the conjugate of the upper sideband signal and the lower sideband signal of the adjacent previous sample are multiplied to obtain the differential signal.
  5. 5. The ISAR distance envelope alignment method based on phase difference according to claim 1, wherein in the step 4, an average phase difference is obtained by performing amplitude weighted phase averaging on the differential signal along the distance direction, the amplitude of the differential signal is weighted by introducing an amplitude square coefficient, and an envelope offset estimation value of adjacent samples is calculated according to the average phase difference, the center frequency difference between the upper sideband and the lower sideband, and the speed of light.
  6. 6. The ISAR distance envelope alignment method based on phase difference according to claim 1, wherein in the step 5, the envelope offset estimation value is converted into a linear phase factor of a distance frequency domain, and the distance frequency spectrum of the compensated signal is multiplied by the linear phase factor and then subjected to inverse fourier transform to realize sub-pixel level displacement of a time domain, thereby obtaining an aligned signal.
  7. 7. The method for ISAR distance envelope alignment based on phase difference as claimed in claim 1, wherein in the step 6, an accumulated memory coefficient is introduced to weight the aligned signal and then add with the next sample to obtain a new accumulated signal, wherein the value range of the accumulated memory coefficient is zero to one, and the accumulated memory coefficient is used for controlling the retention degree of the historical envelope information.
  8. 8. An ISAR distance envelope alignment system based on phase difference, comprising: The compensation module is used for carrying out adjacent sampling average phase compensation processing on the echo signals after pulse compression to obtain compensated signals; The generating module is used for carrying out block processing on the compensated signal in a distance frequency domain, and each azimuth sample generates an upper sideband signal and a lower sideband signal; the differential module is used for carrying out conjugate multiplication processing on four signals of two adjacent samples to obtain differential signals; The estimation module is used for obtaining an estimated value of the envelope offset of the adjacent samples by using the differential signal through maximum likelihood estimation; The alignment module is used for carrying out alignment processing on adjacent samples according to the envelope offset estimation value to obtain aligned signals; And the accumulation module is used for accumulating the aligned signals, and repeatedly carrying out recursion alignment on the accumulated result and next sampling repeated adjacent sampling average phase compensation, distance frequency domain blocking, conjugate multiplication, maximum likelihood estimation and adjacent alignment processing until the envelope alignment of all the samples is completed.
  9. 9. An electronic device, comprising: One or more processors; a memory for storing one or more programs; Wherein the one or more programs, when executed by the one or more processors, cause the one or more processors to implement the ISAR distance envelope alignment method based on phase difference of any of claims 1-7.
  10. 10. A computer readable storage medium having stored thereon executable instructions which when executed by a processor cause the processor to implement the ISAR distance envelope alignment method based on phase difference of any of claims 1 to 7.

Description

ISAR distance envelope alignment method and system based on phase difference Technical Field The invention belongs to the technical field of radars, and particularly relates to an ISAR distance envelope alignment method and system based on phase difference. Background Inverse Synthetic Aperture Radar (ISAR) is an effective means for imaging non-cooperative targets by microwaves, has the characteristics of all-weather and all-weather, and has wide application in the fields of ground-based detection of space-based targets, space-based imaging of orbital vehicles, imaging of sea non-cooperative ship targets and the like. ISAR systems typically transmit chirp signals, acquire range-wise high resolution through pulse compression, and image in azimuth using Doppler differences generated by scattering points of the target. The ISAR imaging process is divided into four steps of envelope alignment, initial phase correction, rotation compensation and azimuth imaging by taking the signals after distance compression as a starting point. The distance envelope alignment is the basis of subsequent processing, and aims to maintain the azimuth signals of all scattering points in the same distance gate, so as to avoid walking caused by azimuth time change. The accuracy of the envelope alignment has a decisive influence on the phase estimation of the azimuth signal and the final imaging quality. Classical distance envelope alignment algorithms rely mainly on envelope magnitude information. Representative methods include an adjacent cross-correlation method, an accumulated cross-correlation method, a gravity center method, a special display point method, an image quality optimization method, and the like. The minimum entropy algorithm is a method with higher reference amount at present, and the envelope offset is estimated iteratively by optimizing the entropy value of the average range profile. However, these amplitude-based algorithms have two inherent drawbacks, namely, firstly, the accuracy is limited by the interpolation multiplying power, high multiplying power up-sampling or interpolation operation is required to realize sub-pixel level alignment, secondly, the calculation speed is slow, and the high multiplying power interpolation and frequent fourier transformation operation result in larger operation amount, so that the real-time processing requirement is difficult to meet. More importantly, the inaccuracy of envelope alignment not only affects the phase, but also introduces amplitude modulation, producing a coherent echo in the image domain that is difficult to compensate. In view of the above problems, some improvements have also been made in the prior art. For example, patent publication number CN106154265B proposes an orthographic radar ISAR envelope alignment method based on frequency domain shift, which realizes accurate shift of range profile by constructing frequency shift factors, breaking through the limitation of 0.5 range resolution units. However, the method still needs to perform coarse alignment, then performs fine search in an exhaustive manner, does not essentially get rid of the dependence on search and interpolation, and has the computational efficiency to be improved. The patent with publication number CN114488149A proposes a global envelope alignment method based on Tsallis entropy minimization, which iteratively estimates the offset by optimizing the Tsallis entropy of the average range profile, but the method still belongs to an amplitude dependent algorithm, and cannot fundamentally solve the contradiction between precision and speed. In addition, although some envelope alignment methods based on phase difference exist, the methods generally depend on fast-changing phases, and complicated phase unwrapping operation is required to obtain correct displacement, so that algorithm robustness is poor, and popularization and application in practical engineering are difficult. Disclosure of Invention In order to solve the technical problems, the invention provides an ISAR distance envelope alignment method and system based on phase difference, which utilize signals after adjacent echo distance frequency domain blocking to perform conjugate multiplication for three times to construct a differential signal containing sub-pixel displacement information, and directly extract envelope offset through amplitude weighted maximum likelihood estimation to realize high-precision rapid alignment without interpolation. In order to achieve the above purpose, the technical scheme adopted by the invention is as follows: An ISAR distance envelope alignment method based on phase difference, the method comprising: step 1, carrying out adjacent sampling average phase compensation processing on echo signals after pulse compression to obtain compensated signals; step 2, performing block processing on the compensated signal in a distance frequency domain, and sampling each azimuth to generate an upper sideband signal and a