Research Of Airborne Wide-Angle Staring Synthetic Aperture Radar Imaging Technique

Wide-Angle Staring synthetic aperture radar(WAS-SAR)whose antenna moves along a curved trajectory while illuminating the observation scene is a kind of SAR system with important application prospect.It can observe the observation target at a wide angle or even 360°in all directions.Compared with conventional SAR,the increase of azimuth observation angle brings three outstanding advantages: firstly,the broadening of azimuth observation angle can provide more comprehensive and rich target scattering information.Secondly,the “shielding effect” in conventional SAR is reduced or even eliminated.Thirdly,the target azimuth spectrum is broadened to obtain higher resolution.WAS-SAR high resolution imaging is based on more complex system techniques and signal processing.At present,imaging processing technology based on WAS-SAR mode is not mature,and there are still few researches on related imaging algorithms,and many technical difficulties remain to be broken through.Based on WAS-SAR mode,this paper is focused on the high resolution imaging processing.The main contributions of this dissertation can be summarized as follows:1.In the aspect of WAS-SAR imaging,Polar Format Algorithm(PFA)is mainly introduced,and the relationship between azimuth resolution and observation accumulation angle and the influence of plane wave approximation on the size of imaging scene are theoretically analyzed.It is helpful to design parameters of WAS-SAR system.The analysis results will form the basis for following study.2.For the small depth of focus(DOF)of PFA which limited WAS-SAR imaging scene to a small region,a large scene high-resolution WAS-SAR imaging algorithm is proposed.Firstly,the scene is segmented into several sub-blocks along the distance direction and imaging each sub-block separately.Then space-variant post-filtering(SVPF)is used to eliminate residual phase errors.This method can effectively expand the WAS-SAR imaging scene and has high computational efficiency.By applying mosaic image method,the position offset and gray difference in the process in the process of SAR image mosaic are eliminated.3.In the aspect of WAS-SAR video imaging,because of the long sub-aperture time and complex motion trajectory,a video SAR imaging method based on three-step motion error compensation method was proposed to solve the problem of motion error compensation.Firstly the coarse compensation based on the inertial navigation measurement parameters is used,then the map-drift(MD)method is used to compensate the secondary phase error,and finally the phase gradient autofocus(PGA)is proposed to eliminate and compensate the residual high-order phase error.The three-step motion error compensation method not only solves the problem of insufficient inertial navigation accuracy but also solves the problem of PGA estimation performance degradation caused by large main lobe broadening.A post-processing method for WAS-SAR video images was proposed to solve the problems of large side-lobe in a single frame image and position offset of the same target in adjacent frames.The proposed method improves the quality of single frame image and eliminates the “jitter” and gray difference in the video.The above research results are verified by airborne WAS-SAR experimental data.The achieved researches in this dissertation have great theory signification and potential application for the high accuracy WAS-SAR imaging.