Study On Imaging Signal Processing For Large Squint Strip Synthetic Aperture Radar

Synthetic Aperture Radar(SAR)imaging has several modes,such as spotlight,stripmap and scanning.The stripmap mode SAR has the advantage of continuous large area imaging compared with the spotlight mode.Most of the existing stripmap SAR systems work in sidelook mode in general.In many application situations,it is necessary to adjust the beam forward or backward in order to obtain the front or rear of the radar platform.Squint mode is one of the most important SAR imaging modes and with high value in military application.However,the research on the high squint mode SAR imaging signal processing is unmature.Highly squinted stripmap SAR signal processing faces two difficulties: One is the severe range azimuth coupling caused by the large deviation angle;Another is the difficulty in implementation of real-time full aperture SAR processing.The Polar Format Algorithm(PFA)uses polar coordinates to storage data and its imaging accuracy is not related to squint angle.It can effectively solve the problem of high-precision imaging under high-squint situation.Moreover,PFA is simple and efficient,and is suitable for complex radar tracks compared with other imaging algorithms.Therefore,it has good application prospects under large maneuver and large squint situations.However,the PFA is a classical spotlight SAR imaging algorithm which can not be used directly to process the stripmap SAR data.In this paper,the full aperture SAR data is divided into subapertures and the improved polar format algorithm is applied to each subapertures.Then with seamlessly splicing the imaging results of each subapertures to realize the high-precision real-time imaging processing of the large squint stripmap SAR.The main work of this paper is as follows:Chapter 1 is the introduction.Starting from the research background and significance,this paper reviews the SAR skills and its origin.Then,analyzes the domestic and foreign research status of SAR imaging technology,and introduces the main work and structure of this paper.Chapter 2 is the study of PFA.First is to introduce the principle of PFA imaging,and then introduced the PFA geometric model,analyzed polar format conversion process from the range migration correction.Then the PFA is simulated and verified by point target simulation.Based on the analysis of the wave front bending effect,the geometric distortion correction is studied and the geometric distortion correction effect is simulated and verified.Chapter 3 is the study of data processing of the beam with subapertures.First is to compare the stripmap mode SAR and the spotlight mode SAR,analyse the signal model of stripmap SAR and spotlight SAR.Then the conversion principle of stripmap mode data to spotlight mode data is expounded.In order to obtain the subaperture PFA image,this chapter uses the classical PFA,to do filtering processing of subaperture image based on spatial domain transform.Finally,simulation results are used to analyze the applicability of PFA imaging of subaperture strip data.Chapter 4 is the study of the strip data splice processing.A new algorithm of SAR subaperture stitching image processing based on PFA is presented in this chapter.The new algorithm solved the problem of high precision imaging of the subaperture in the high precision with improved PFA.The real-time imaging of the full aperture is realized through the stitching imaging principle of the subaperture image and the validity of the proposed algorithm is verified by the point target simulation and the measured data processing.Finally,concluding remarks on the full text of the work are summarized,and prospect the problems needs to be further study.