Study On Moving Targets Imaging Technology For Spaceborne SAR

Compared with optical imaging,synthetic aperture radar(SAR)has the ability to work in day/night,all-weather and wide-range imaging conditions.For spaceborne platform,its vast coverage of the imaging scene and the availability of data are superior than those of other platforms.After full development of the past several decades,images of high resolution can be acquired by the traditional SAR imaging algorithms for ground stationary targets,which are invalid for ground moving targets in the imaging scene and result in imaging blurring as well as bias in target location.All these have a severe compact on imaging quality and subsequent interpretation on images.With the increasing demand for imaging quality,the research on spaceborne SAR ground moving targets imaging in the military and civilian fields has also gradually enlarged.In this context,the research is unfolded to solve ground moving target imaging problems The main work is as follows: 1.On the basis of establishing the model of SAR echo signal,the important parameters related to imaging are introduced.By combining some knowledge of signal and system,analysis on the SAR imaging system model is conducted,followed by the widely used Range-doppler(RD)imaging algorithm for stationary targets to underlay the subsequent study of moving targets.2.By analyzing airborne ground moving target echo signals and combining with the characteristics of satellite platform,we establish the echo signal model of the spaceborne ground moving target in the side-looking mode.Then,the ideal ground moving target imaging algorithm with known motion parameters is given,and the effect of motion parameters on the SAR imaging quality is fully analyzed.3.The traditional ground moving target imaging algorithms firstly detect targets and estimate the motion parameters for prior information with the following target imaging.However,it is difficult to detect moving targets and estimate motion parameters in the low signal-toclutter-noise ratio condition.This thesis studies the instantaneous range-Doppler(IRD)algorithm that can perform ground moving target imaging without a priori knowledge of accurate motion parameters.Through deramp-keystone processing(DKP),the IRD algorithm focuses the moving target at a selected position in the range-Doppler domain.The keystone transform realized by the sinc interpolation kernel is not conducive to engineering implementation.In this thesis,we propose a substitution of the Knab interpolation kernel for the sinc one in the Keystone transform processing.Experimental results demonstrate that our porposed method ensures the accuracy of algorithm with a considerable improvement on computational efficiency.