Research On The Modification Of Chirp Scaling Algorithm Of Sar Based On Nonlinear Trajectory And High Speed Motion

Synthetic aperture radar(SAR)is a kind of high-resolution imaging radar of all-day and all-weather.The radar constructs an equivalent synthetic aperture antenna through azimuth movement,and then uses pulse compression technology to obtain two-dimensional high-resolution images in range and azimuth direction.It is widely used in military and civil fields,and is an indispensable observation means.In the research of SAR systems on different platforms,spaceborne SAR is not limited by the sovereignty of the airspace,so it has been paid attention by all countries in the world.At present,there are dozens of spaceborne radars in orbit in the world,and the imaging algorithm of high-resolution spaceborne SAR has always been the focus of research.The difficulty of high-resolution spaceborne SAR imaging research is that when the orbit of Spaceborne Radar rises,the speed speeds up and the synthetic aperture time becomes longer,the traditional imaging algorithm based on the orbit straight line approximation and the “stop-and-go” hypothesis is no longer applicable.It is necessary to improve the algorithm by establishing more accurate slant range model and echo model to obtain high-resolution images.Therefore,based on the traditional Chirp Scaling(CS)Algorithm,this thesis improves and simulates the imaging algorithm under the assumption of nonlinear trajectory and the failure of “stop-and-go” hypothesis.Firstly,based on the principle of SAR,the generation of LFM signal,the principle of pulse compression and the reason why the radar image has two-dimensional high resolution are introduced.Then,the echo simulation process of point target under the linear trajectory slant range model and “stop-and-go” hypothesis is discussed.The principle of traditional CS algorithm and range migration correction under the model are introduced in detail,and the point target imaging is completed Simulation.Because SAR can't always work in linear orbit,the error of linear orbit will bring the error of imaging results.This thesis focuses on the establishment of nonlinear trajectory model and imaging,discusses the difference of the longest synthetic aperture time between the ESRM and the AHRM in medium and high orbit,and obtains the improved CS imaging algorithm.The point target simulation results under the traditional algorithm are compared to illustrate the importance of accurate slant range model for high-resolution imaging of radar system.Aiming at the “stop-and-go” hypothesis,this thesis introduces the accurate echo model under the failure of “stop-and-go” hypothesis,and improves the traditional CS algorithm according to the echo model.Through the comparative analysis of the simulation results of the two algorithms under different radar speeds,it shows that the“stop-and-go” hypothesis will lead to poor imaging quality in high-speed moving radar system,which further illustrates the failure of “stop-and-go” hypothesis is necessary to improve the imaging algorithm.Finally,the effectiveness of the two improved CS algorithms is proved by imaging the measured satellite data,which provides ideas and basis for the improvement of high-resolution imaging algorithm in more complex cases.