任意构型双基SAR运动目标图像特征分析

Image Feature Analysis of Moving Targets in Bistatic SAR Under Arbitrary Configuration

本文根据波数域中的相位误差详细地分析了任意构型双基合成孔径雷达(Bistatic Synthetic Aperture Radar,Bi-SAR)运动目标的图像特征。不同于传统的在相位历史域进行相位误差分析的方法,本文以极坐标算法(Polar Format Algorithm,PFA)为例,对PFA波数域的两维相位误差进行了详细的分析。该分析方法对其他算法例如BP算法同样适用。SAR成像算法的一般流程为,先将信号从相位历史域转化到波数域,然后再变换到图像域。然而,从相位历史域到波数域的过程有可能引入新的相位误差,因此在相位历史域分析相位误差特征并不完全准确,根据该特性预测的图像域成像结果存在一定的误差。而波数域与图像域之间具有直接的傅里叶变换关系,傅里叶变换的各种性质又是已知的,因此利用波数域和图像域之间的傅里叶变换关系,根据波数域的相位误差特性可以准确地预测PFA图像中运动目标的成像特征。一方面,本文揭示了波数域中的两维相位误差导致图像域中的目标发生两维位置偏移和两维散焦的现象,并且上述两维位置偏移和两维散焦的方向沿着同一条倾斜的直线。也就是说,无论运动目标的速度矢量指向何方,图像域中的目标都将沿着同一条直线发生偏移。另一方面,通过一个合适的坐标旋转,能使相位误差的维度从两维降到一维,从而能够降低后续的目标重定位与重聚焦的难度和复杂度。最后,通过仿真实验验证了对PFA图像中运动目标特性的预测结果。

In this paper,the image feature analysis of the moving target in bistatic synthetic aperture radar(bi-SAR)un⁃der arbitrary configuration has been studied in detail based on phase error in the wavenumber domain.Different from the conventional approach where phase error analysis is performed in the phase history domain,in this paper,we provided a detailed analysis of the 2-D phase error in the PFA wavenumber domain.The analysis method is also applicable to other al⁃gorithms such as the BP algorithm.The general process of SAR imaging algorithm involved converting the signal from the phase history domain to the wavenumber domain,and then transforming it to the image domain.However,the process of converting signal from the phase history domain to the wavenumber domain may introduce new phase errors.Therefore,analyzing the characteristics of phase error in the phase history domain may not be entirely accurate.As a result,there may be some errors in the imaging results predicted by the characteristics observed in the wavenumber domain.Since there is a direct Fourier transform relationship between the wavenumber and image domains,and the properties of the Fourier transform are already well-known,we can accurately predict the imaging characteristics of moving target in the PFA imag⁃ery by using the Fourier transform relationship between the two domains and considering the phase error characteristics ob⁃served in the wavenumber domain.This article presents a significant finding that the 2-D phase error in the wavenumber domain can lead to a 2-D position shift and defocusing of targets in the image domain,both occurring along a skewed straight line.This means that,regardless of the direction of the moving target motion,the image of the moving target in the image domain will consistently shift in a specific line.Alternatively,by implementing an appropriate coordinate rotation,the dimension of the phase error can be reduced from 2-D to 1-D.This simplification of the phase error dimension can,in turn,minimize the complexity and difficulty of relocating and refocusing on the target in the image domain.Finally,the simulation experiments are carried out to verify the predicted signatures of the moving target in PFA imagery.