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CN-121978689-A - Airborne large squint SAR imaging method based on two-dimensional wave number spectrum resampling

CN121978689ACN 121978689 ACN121978689 ACN 121978689ACN-121978689-A

Abstract

The invention discloses an airborne large squint SAR imaging method based on two-dimensional wave number spectrum resampling, which constructs an azimuth defuzzification function, corrects an aliased azimuth wave number spectrum generated under the PRF limited condition and provides complete two-dimensional wave number spectrum data for subsequent processing. The method corrects the aliased azimuth wave number spectrum by using the azimuth deblurring function, and then uses a two-dimensional wave number spectrum resampling factor in the subsequent operation to perform two-dimensional resampling and equivalent transformation on the squint two-dimensional wave number spectrum into a wave number domain signal of a front side view, thereby improving the utilization rate of the wave number spectrum. The method can correct the aliased azimuth spectrum under the PRF limited condition of the airborne high squint SAR, and realize the two-dimensional high-resolution imaging of the target area by an imaging method of resampling the two-dimensional wave number spectrum, thereby widening the engineering application scene.

Inventors

  • ZHAO YONGBO
  • SONG YANG
  • GAO DI

Assignees

  • 西安电子科技大学

Dates

Publication Date
20260505
Application Date
20260204

Claims (10)

  1. 1. An airborne large squint SAR imaging method based on two-dimensional wave number spectrum resampling is characterized by comprising the following specific steps: Step 1, performing distance dimension conversion on an acquired airborne large squint SAR baseband echo signal to obtain a distance wave number domain signal; Step 2, correcting an aliasing azimuth wave number spectrum generated under the PRF limited condition to obtain a two-dimensional wave number domain signal of the effective support domain; Step 3, performing distance matching filtering and unified phase compensation on the two-dimensional wave number domain signal, and compensating the distance-azimuth coupling phase to obtain a compensated two-dimensional wave number domain signal; And 4, resampling the two-dimensional wave number spectrum to the two-dimensional wave number domain signal according to the mapping relation defined by the two-dimensional resampling factor, enabling the equivalent transformation to represent the wave number domain signal in a front side view mode, and carrying out two-dimensional inverse transformation on the resampled signal to obtain the SAR image focused in the distance-azimuth space domain.
  2. 2. The on-board large squint SAR imaging method according to claim 1, wherein the expression of the distance wave number domain signal in step 1 is as follows: ; Wherein, the Two-dimensional signals representing the distance dimension in the wave number domain and the azimuth dimension in the space domain, the former character representing the distance dimension and the latter character representing the azimuth dimension, capitalization Representing the wavenumber domain, lowercase Representing a spatial domain; The distance-wise wave number variable is represented, Representing the wavenumber domain representation of the distance envelope, Representing the azimuth sampling position of the carrier platform, Representing the spatial domain representation of the azimuthal envelope, Representing the slant distance of the beam center as it sweeps across the target, Expressed in natural constant As a function of the base of the exponentiation, Representing the sign of the imaginary unit, The circumference ratio is indicated as such, The speed of light is indicated as being the speed of light, Indicating the distance-wise frequency of adjustment, Representing the distance to the centre of the wave number, Representing the carrier frequency of the transmitted signal, , Represents the range of distance-wise wave number values, Representing the width of the transmitted pulse, The instantaneous pitch is indicated as such, Indicating azimuth slow time.
  3. 3. The method for imaging the airborne high squint SAR according to claim 2, wherein in the step 2, the correction of the aliasing azimuth wavenumber spectrum generated under the PRF limited condition means that the azimuth-dimension phase after preprocessing is obtained by multiplying a distance wavenumber domain signal with an azimuth disambiguation function, and then the two-dimensional wavenumber domain signal of the effective support domain is obtained by adopting azimuth-dimension transformation in the same way as distance-dimension transformation.
  4. 4. The on-board high squint SAR imaging method according to claim 3, wherein said azimuth disambiguation function is as follows: ; Wherein, the Representing the orientation de-blurring function, Representing the beam center squint angle.
  5. 5. The airborne high squint SAR imaging method of claim 4, wherein the preprocessed azimuth dimension phase is obtained by multiplying a distance wave number domain signal with an azimuth defuzzification function, and the expression is as follows: ; Wherein, the Representing the slant distance of the beam center as it sweeps across the target.
  6. 6. The on-board high squint SAR imaging method according to claim 5, wherein said azimuth dimension transformation is obtained by: ; Wherein, the Representing a two-dimensional signal with a distance dimension in the wave number domain and an azimuth dimension in the wave number domain, Represents the azimuthal wavenumber vector, The wavenumber domain representation of the azimuthal envelope, Representing the azimuthal distance of the target relative to the center of the scene.
  7. 7. The airborne large squint SAR imaging method of claim 6, wherein the distance direction matched filtering in the step 3 is to multiply a two-dimensional wave number domain signal with a distance matched filtering function to obtain a distance direction pulse compressed two-dimensional wave number domain signal, and the expression is as follows: ; ; Wherein, the Representing a distance matching filter function; representing a two-dimensional signal with a distance dimension in the wave number domain and an azimuth dimension in the wave number domain, Represents the azimuthal wavenumber vector, The wavenumber domain representation of the azimuthal envelope, Representing the azimuthal distance of the target relative to the center of the scene.
  8. 8. The airborne large squint SAR imaging method according to claim 7, wherein the unified phase compensation in step 3 is to multiply the compressed signal with a unified phase compensation function to obtain a two-dimensional wave number domain signal after phase compensation, and the expression is as follows: ; ; Wherein, the Representing a unified phase compensation function, Representing the central slant distance of the scene, Representing a cosine-solving operation, Representing the phase compensated two-dimensional wave number domain signal.
  9. 9. The method for imaging the onboard high squint SAR of claim 8, wherein in the step 4, the two-dimensional wavenumber spectrum resampling is performed on the two-dimensional wavenumber domain signal according to a mapping relation defined by a two-dimensional resampling factor, and the expression is as follows: ; ; Wherein, the Representing the distance-wise wavenumber vector after two-dimensional resampling, Represents the azimuth wavenumber vector after two-dimensional resampling, Representing the wave number domain signal after two-dimensional resampling.
  10. 10. The on-board large squint SAR imaging method according to claim 9, wherein said two-dimensional inverse transformation of the resampled signal in step 4 is obtained by: ; Wherein, the Representing a two-dimensional signal with a distance dimension in the spatial domain and an azimuth dimension in the spatial domain, Representing a sinc function 。

Description

Airborne large squint SAR imaging method based on two-dimensional wave number spectrum resampling Technical Field The invention belongs to the technical field of radar imaging, and further relates to an airborne large strabismus SAR imaging method based on two-dimensional wave number spectrum resampling in the technical field of signal processing and imaging algorithms. The invention can be used for inhibiting azimuth spectrum aliasing of the airborne large squint synthetic aperture radar SAR (Synthetic Aperture Radar) under the condition of limiting the pulse repetition frequency PRF (Pulse Repetition Frequency), and realizes the two-dimensional high-resolution accurate focusing imaging of the target area by an imaging method of resampling a two-dimensional wave number spectrum. Background According to the difference between the frequency domain mapping model and the resampling mode, the Omega-K imaging method under the strabismus condition can be summarized into three types, namely a strabismus Omega-K algorithm based on the traditional Stolt interpolation, a strabismus Omega-K algorithm based on the extended Stolt interpolation and a strabismus Omega-K algorithm interpolated along the sight line direction. The error phase of the traditional Stolt interpolation method is difficult to be explicitly separated, so that the motion error is difficult to be embedded into an imaging process in an analytic form, and therefore the motion error is difficult to be effectively connected with a conventional motion compensation method. To improve this problem, NAIVEDYA MISHRA et al propose an extended Stolt interpolation strabismus Omega-K method that explicitly preserves the motion error in the azimuth modulation phase while maintaining the distance and azimuth processing relatively independent, facilitating the subsequent compensation. On the other hand, the two-dimensional wave number spectrum under the strabismus imaging can be obviously inclined stretched and distorted, namely, the effective resampling area available when the internal rectangular interpolation is adopted is obviously reduced, and the external rectangular interpolation is adopted, so that the edge of the supporting area is required to be subjected to interpolation and alignment in a larger range, and extrapolation errors and calculation cost are increased. The first two methods have relatively low utilization of the supporting region of the squint two-dimensional wavenumber spectrum, which inevitably limits the imaging quality. In contrast, the wave number spectrum supporting area in the strabismus coordinate system is equivalently converted into a positive side view form through two-dimensional rotation resampling along the line-of-sight interpolation method, so that the effective data duty ratio is increased, the focusing effect is improved, but in order to inhibit azimuth blurring and azimuth wave number spectrum aliasing caused by azimuth blurring under the condition of large strabismus, higher PRF (pulse rate filter) support is generally required, and the system parameter configuration is subject to stricter constraint. The national academy of sciences ' space-sky information innovation institute discloses a satellite-borne large strabismus multi-mode SAR integrated imaging method and device in patent literature ' a satellite-borne large strabismus multi-mode SAR integrated imaging method and device ' (application number 202510641571.1 application publication number CN 120161468A). The method comprises the steps of carrying out Fourier transformation on multi-mode SAR data along a distance direction, carrying out azimuth deskewing and distance direction compression processing, eliminating Doppler spectrum aliasing based on azimuth sub-bands, carrying out reference point matched filtering on the data after eliminating Doppler spectrum aliasing, carrying out distance direction block and differential matched filtering on the data after carrying out the reference point matched filtering, carrying out two-dimensional frequency domain resampling on the data after carrying out the distance direction block and the differential matched filtering, and carrying out two-dimensional time domain block and differential matched filtering again to obtain a fine focusing imaging result. The method realizes large squint multi-mode satellite-borne SAR Doppler spectrum aliasing and full scene fine focusing under the condition of only increasing a small amount of data. However, the method still has the defects that the processing chain depends on multiple blocks, differential matched filtering and two-dimensional resampling, the adaptability to the PRF limited conditions is still insufficient, the azimuth spectrum aliasing caused by Doppler center offset under the middle-low PRF is more likely to cause incomplete supporting domain, and the stability of the subsequent two-dimensional resampling and fine focusing processing is reduced. Disclosure of Invention The inv