Study On Moving Targets High Resolution Imaging In Synthetic Aperture Radar

As a tool of microwave remote sensing,synthetic aperture radar(SAR)is characterized by all-day,all-weather,and high-resolution,and has been widely used in both military and civilian applications.In recent years,with the rapid development of SAR technology,the standards of SAR image resolution are getting higher.In order to meet the requirements of SAR high-resolution,people try hard to research effective methods of motion compensation.Meanwhile,in many applications,people pay more attention to moving targets in the static scene,people sometimes even hope to get categories and models and other details of targets,so it is great significance of move target imaging.Static scene high resolution imaging and moving targets imaging are key issues in the field of Synthetic Aperture Radar.However,there are many difficulties in the process.First,the suboptimal motion of the carrier will affect the parameter estimation,which eventually leads to blurring and defocus of the images.Second,due to the randomness of moving targets,conventional image forming method can't work normally.This dissertation focuses on two aspects,those are high-resolution motion compensation and moving targets imaging.The innovation of this paper mainly has the following four points.1.The PGA window function is improved,make it to be more close to the size of the support domain,this change can improve the estimation accuracy and convergence speed.2.Autofocus algorithm based on minimum entropy is improved with binary search.This improvement can reduce the calculation and improve the efficiency of imaging.3.A PGA algorithm based on time-frequency analysis is proposed and the computer simulation and the real Synthetic Aperture Radar data are used to test this algorithm.4.A new method of constant acceleration moving target imaging based on Chirp Scaling is proposed.The main content of this dissertation is summarized as follows.1.The principle of SAR imaging is discussed and motion error of airborne SAR is analyzed.In this chapter,the SAR imaging methods is discussed from signal processing.At the same time,the Range Doppler algorithm as a most common imaging algorithm is studied and its concrete steps in low squint and high squint are given.The effect of motion error on imaging quality is also studied.2.The classical PGA algorithm is studied and its advantages and disadvantages are analyzed.The window function of PGA is improved in this paper.Then some Doppler parameters estimation algorithms are introduced.The dissertation studies autofocus algorithm based on minimum entropy and improves it with binary search.This improvement can reduce the calculation and improve the efficiency of imaging.The end of this chapter,a PGA algorithm based on time-frequency analysis is proposed and the computer simulation and the real Synthetic Aperture Radar data are used to test this algorithm.3.The geometric model of ground move target is established and the effect of the moving targets is analyzed.Then,the moving target imaging algorithm based on two order Keystone transform is introduced and the theoretical result of this algorithm is given.Finally,a new method of moving target imaging based on constant acceleration is proposed,this algorithm is improved on the basis of Chirp Scaling algorithm.The computer simulation and the real SAR data are used to test this algorithm.