Research On Autofocus Processing Method Of Bistatic SAR Motion Error

Synthetic Aperture Radar(SAR)is widely used in various fields because of its many advantages such as all-day and all-weather.Airborne bistatic SAR places the transmitting and receiving systems on two separate platforms,which makes it have good stealth and anti-jamming capability,and has wide applications in both military and civilian fields.Bistatic SAR motion error autofocus processing method is to estimate the motion error from the bistatic SAR echo data and compensate the motion error by the autofocus processing method in the presence of motion error,thus realizing the high-precision imaging of bistatic SAR.In this thesis,for the demand of bistatic SAR high-precision imaging applications,the research on echo modeling,motion error modeling,autofocus algorithm and spatialvariation error compensation method of bistatic SAR is carried out around the image scattering problem caused by the motion error of airborne radar platform,and the main research contents are as follows:1.The bistatic SAR geometric model and echo signal model are established,and the distance migration characteristics and spatial-variant Doppler characteristics of bistatic SAR echoes are analyzed.The bistatic SAR motion error model is established,and the image scattering and phase spatial-variation problems under the measured trajectory are analyzed,which lays a theoretical foundation for the subsequent study of bistatic SAR motion compensation algorithm.2.The imaging principle and implementation steps of the time-domain Back Projection(BP)algorithm are studied.Based on this,the evaluation criteria of image quality are analyzed,and the iterative optimization algorithm based on image entropy and the geometric solution method based on image sharpness are studied.3.To address the problem of image scattering caused by spatial-variation error,a spatial-variant motion error compensation method via joint-refocusing of multisubimages for bistatic SAR is proposed,which realizes the estimation and compensation of spatial-variation motion error through the steps of sub-region phase error estimation,joint solution of 3D motion error,trajectory reconstruction and back-projection,so as to obtain a consistent focused image of the observed scene.In this thesis,the effectiveness and accuracy of the above method are verified through theoretical analysis and simulation experiments on actual measurement data,and the simulation results show that the above method can achieve the focusing of bistatic SAR scattered images and obtain bistatic SAR high-resolution images.