Research On SAR/ISAR Imaging Method For Space Target

Imaging radar with the advantages of full-time,all-weather,long detection range,and high resolution is one critical technique for the detecting,categorizing and tracing of space targets with attempt to secure the operation of spacecraft.This paper conducts an in-depth investigation on the SAR/ISAR imaging methods of space targets basing on the ISAR imaging theory of airplane targets.First of all,this paper analyzes existing ISAR imaging theories including basic principles,processes and algorithms finding that the stable-flying airplane target after undertaking motion compensation roughly equals to a rotating target which rotates around the center with constant speed,and we can acquire its clear ISAR image using Range-Doppler(R-D)algorithm.This paper uses both simulation data and measured data to test the effectiveness of several common motion compensation algorithms followed by their performances comparison.The echo Doppler frequency of maneuvering flight target,which rotates with a constant speed in relative to radar line of sight liner changes with slow time.The traditional R-D algorithm would significantly reduce the ISAR imaging quality of maneuvering flight target because of the cross-range direction Spectrum broadening;and the farther the scattering point is from the Doppler phase center,the more severe the spectrum broadening phenomenon.However,by using the time-frequency analysis-based imaging method and the CLEAN-based RID imaging method,we can effectively eliminate the cross-range direction spectrum broadening.Then,this paper analyzes the motion characteristics of space targets,and then constructs orbit model of space target.By using STK software,this paper creates two observation models: ground-based ISAR and space-borne radar for space target,and then analyses the echo characteristics of the two observation model s.Beside,this paper simulates the ground-based ISAR and space-borne radar for space target on the basis of the existing motion compensation algorithms and imaging algorithms,primarily achieving the space target imaging of the two observation models.And,this paper achieves clear images of the space target based on measured data from space-borne radar.Finally,this paper takes the ground-based ISAR observation model of space target as an example,to analyze the influence of the radial velocity of the space target on the distance-to-pulse pressure performance.This paper discusses two existing speed compensation algorithms: the RWT-based speed compensation and the FrFT-based speed compensation before proposing the Chirplet transform-based speed compensation algorithm.After analyzing the principles of the proposed algorithm,this paper has algorithm simulation to test its effectiveness,and finds that the Chirplet transform-based speed compensation algorithm can effectively eliminate the impact of radial velocity and achieve clear image of space targets.