CN-120044527-B - PFA imaging and motion error compensation method for unmanned aerial vehicle SAR

CN120044527BCN 120044527 BCN120044527 BCN 120044527BCN-120044527-B

Abstract

The invention discloses a PFA imaging and motion error compensation method of unmanned aerial vehicle SAR, which belongs to the technical field of unmanned aerial vehicle SAR imaging, and mainly solves the problem of phase error coupling effect caused by unmanned aerial vehicle platform attitude disturbance so as to improve the accuracy and reliability of SAR imaging results. The method comprises the following steps of processing stripe signals to realize conversion from stripe mode to beam-like mode, then implementing polar coordinate format algorithm (PFA) to carry out distance frequency modulation, distance unit migration linearization and wedge transformation, then obtaining residual distance unit migration (RCM) through cross-correlation estimation, constructing a coarse compensation term to reduce most of motion errors, then carrying out motion error fine compensation by utilizing minimum entropy self-focusing algorithm (MEA), and finally generating SAR images through two-dimensional Fast Fourier Transformation (FFT).

Inventors

ZHAO SIHANG
ZHANG QIANQIAN
LI YINWEI
LI WEISONG
YANG YULIN
SHI XIANGXIANG
LI BAIYANG
WANG CHENCHEN

Assignees

上海理工大学

Dates

Publication Date: 20260508
Application Date: 20250228

Claims (5)

1. The polar coordinate format algorithm PFA imaging and motion error compensation method of the unmanned aerial vehicle SAR is characterized by comprising the following steps of: s1, processing a strip signal, selecting a beam-like region, and converting data from a strip mode to a beam-like mode through a specific phase compensation function and an azimuth de-chirp function, wherein the method specifically comprises the following sub-steps: S11, selecting a similar bunching region, and determining a common detection region omega a as similar bunching detection data when the strip azimuth accumulation length L a is larger than the equivalent bunching azimuth accumulation length L s , wherein the width of the equivalent bunching region meets a specific formula: Wherein Lambda is the wavelength; And S12, performing phase compensation, wherein the function for phase compensation is as follows: , Wherein R a (t) is a function of the distance from the radar antenna phase center to the scene center over time; s13, realizing azimuth de-chirp, and obtaining a two-dimensional de-chirp signal of beam combination conversion after phase compensation and azimuth de-chirp, wherein the function of azimuth de-chirp is as follows: ; s2, PFA is implemented, distance frequency modulation is firstly carried out, linear distance unit migration is carried out, and finally wedge-shaped conversion is carried out, so that signal two-dimensional decoupling is completed; S3, performing motion error coarse compensation, obtaining residual error distance unit migration by using cross-correlation estimation, deducing total phase error according to the linear relation between the residual error distance unit migration and azimuth phase error, constructing a coarse compensation term, and processing a preprocessing signal; S4, after PFA is completed, performing motion error fine compensation by adopting a minimum entropy self-focusing algorithm; S5, performing two-dimensional fast Fourier transform on the signals subjected to the series of processing to obtain a compressed image, and generating a final terahertz stripe SAR image.
2. The method for PFA imaging and motion error compensation in polar format for unmanned aerial vehicle SAR according to claim 1, wherein S2 comprises the following sub-steps: s21, distance frequency modulation, wherein a modulation formula is as follows: , Wherein the method comprises the steps of Is the frequency scaling scale, phi ref is the reference pitch angle, phi is the instantaneous pitch angle, theta is the azimuth angle, f c (δ r -1) represents the offset in S signal2 (n, tau); s22, performing migration linearization on the distance unit, and transforming azimuth angles to azimuth time, wherein the transformed signals satisfy the formula: , Where Ω=v a / R c denotes the angular velocity of the radar platform motion, V a the platform velocity, and ; S23, wedge-shaped transformation is carried out, so that the wedge-shaped transformation of the signals is completed, two-dimensional decoupling of the signals is realized, and the decoupled signals satisfy the formula: , Wherein the method comprises the steps of 。
3. The method for PFA imaging and motion error compensation in polar format for unmanned aerial vehicle SAR according to claim 2, wherein S3 comprises the following sub-steps: S31, performing cross-correlation estimation residual distance unit migration, estimating the misalignment of adjacent distance sections by using a rapid banded signal interferometry at each azimuth moment, obtaining a differential motion error ddelta through specific operation, and obtaining the error by item integration; s32, constructing and processing a rough compensation term, constructing a rough compensation term H (t) according to the error term, performing rough compensation on the pre-processed signal to obtain a rough compensation signal, wherein the residual error after the rough compensation satisfies the formula: , , where R b (t) is the fundamental term for differential distance and R e (t) is the distance error term.
4. A polar format algorithm PFA imaging and motion error compensation method for an unmanned aerial vehicle SAR according to claim 3, wherein S4 comprises the following sub-steps: The minimum entropy self-focusing algorithm is adopted, the image entropy is used as an optimization criterion, the image entropy is minimized by adjusting the phase error parameter, the further compensation of the residual error is realized, and the calculation formula of the image entropy E is as follows: , where M and N are the number of rows and columns, respectively, of the image and p ij is the probability of the image normalized by the pixel value at the (i, j) position.
5. The method for PFA imaging and motion error compensation in polar format for unmanned aerial vehicle SAR according to claim 4, wherein S5 comprises the following sub-steps: Performing two-dimensional fast fourier transform on the signal subjected to the series of processing, namely performing two-dimensional fast fourier transform on S A2 (t, f r ) to obtain a compressed image, and generating a final terahertz stripe SAR image, wherein the image coordinates satisfy a specific formula: , where x and y represent the azimuthal and distance coordinates of the image, respectively.

Description

PFA imaging and motion error compensation method for unmanned aerial vehicle SAR Technical Field The invention relates to the technical field of unmanned aerial vehicle Synthetic Aperture Radar (SAR) imaging, in particular to a PFA imaging and motion error compensation method based on unmanned aerial vehicle SAR. Background The synthetic aperture radar (SYNTHETIC APERTURE RADAR, SAR) is used as a high-resolution active microwave remote sensing means, and takes an important role in the fields of military reconnaissance and national resource monitoring by virtue of the all-weather and long-distance imaging advantages. In recent years, along with the fusion development of unmanned aerial vehicle platforms and SAR technology, unmanned aerial vehicle SAR systems exhibit remarkable technical advantages that SAR frequency ranges are 0.1-10THz, and the special millimeter-level wavelength characteristics provide physical basis for realizing centimeter-level ultrahigh resolution imaging, and the unmanned aerial vehicle platforms endow the systems with stronger maneuvering deployment capability and complex terrain adaptation capability. The conventional SAR imaging has two major core challenges, namely, a polar coordinate format algorithm (PFA) is used as a classical imaging algorithm, the narrow-angle scanning characteristic of the SAR can be effectively matched, but the conventional design is oriented to a bunching mode SAR, the problem of wavefront bending compensation mismatch exists when the strap mode is applied, imaging geometric distortion is caused, the sensitivity of the system to micro-motion errors of a platform is improved by orders of magnitude due to the wavelength characteristic of the SAR, and the conventional motion compensation method based on a distance-Doppler algorithm has theoretical limitation when processing two-dimensional space-variant errors, and particularly, the error space-variant effect is more remarkable under the ultra-high resolution condition. In the prior art, a wave number domain reconstruction mode is mostly adopted for PFA improvement of the strip SAR, but the phase error coupling effect caused by unmanned aerial vehicle platform attitude disturbance is not fully considered. In terms of motion compensation, the conventional envelope alignment method is difficult to meet the SAR sub-millimeter precision requirement, and the self-focusing algorithm based on the image domain is limited by the azimuth space-variant characteristic of the stripe mode. It is particularly notable that when resolution is better than 5 cm, the motion error can produce coupling phase errors of tens of wavelengths in the distance and azimuth directions, which directly results in image defocus and geometric positioning bias. Based on this, how to design a PFA imaging and error compensation method of an unmanned aerial vehicle SAR to overcome the above limitations and improve the accuracy and reliability of the imaging result is an important topic to be solved currently. Disclosure of Invention The invention aims to provide a PFA imaging and motion error compensation method of an unmanned aerial vehicle SAR. The method is focused on solving the imaging problem caused by poor stability of the unmanned aerial vehicle in the flight process, and the accuracy and quality of SAR imaging are remarkably improved by accurately measuring the motion error of the unmanned aerial vehicle platform and carrying out real-time compensation by combining echo data. The invention can effectively compensate motion errors, improve image focusing effect, further improve the universal remote sensing capability of the unmanned aerial vehicle under complex meteorological conditions, and meet the requirements of urban construction survey, agricultural general survey, disaster monitoring and other fields for high-precision imaging. The technical files for realizing the purpose of the invention are as follows, the invention provides a PFA imaging and motion error compensation method of unmanned aerial vehicle SAR, which comprises the following key steps: S1, firstly, carrying out processing on a strip signal, selecting a beam-like region, and realizing the conversion of data from a strip mode to a beam-like mode through a specific phase compensation function and an azimuth Dechirp function, thereby laying a foundation for subsequent processing. And S2, implementing a polar coordinate format algorithm (PFA), firstly performing distance frequency modulation, changing a signal frequency structure, linearizing migration of a distance unit, and finally performing wedge-shaped transformation to complete signal two-dimensional decoupling and eliminate two-dimensional coupling of signals. S3, performing motion error rough compensation, obtaining residual range unit migration (RCM) by using cross-correlation estimation, deriving a total phase error according to the linear relation between the residual range unit migration (RCM) and an Azimuth Pha