Study On Imaging Algorithm For Sliding Spotlight SAR

Sliding spotlight mode is a new mode of Synthetic Aperture Radar imaging. Bycontrolling the speed of antenna footprint to control azimuth resolution, this mode has largerimaging areas compared with the spotlight SAR and a higher azimuth resolution than thestrip-map SAR with the antenna of the same size. In recent years, sliding spotlight SAR hasbecome one of the research focuses in the SAR field. Similar as other SAR systems, imagingprocessing is still the key issue. Because of the large difference in aspects of antenna pointingvariation, traditional imaging algorithms used in strip-map SAR and spotlight SAR could notbe applied to process the data directly. This paper makes a deep study on the imagingalgorithms for sliding spotlight mode.This paper firstly describes the principle of SAR imaging and introduces the concept ofrange resolution, azimuth resolution and range migration. Then the paper derives the rawsignal function of point target, analyzes the system performance and compare s the three SARmodes in echo equation, azimuth resolution, Doppler history, azimuth swath width and so on.The advantage of sliding spotlight SAR is summarized after comparison of the three modes.Further more, three relatively mature algorithms for sliding spotlight SAR have beenstudied. The paper focuses on the two-step algorithm which is with the highest imagingprecision. The first step of two-step algorithm is azimuth filtering processing, the purpose ofwhich is to overcome the important problem in sliding spotlight SAR, i.e., spectral foldingphenomenon. After this step the echo is converted to strip-map data. Then in the second step,traditional imaging algorithms in strip-map SAR could be used for imaging, among which theimaging algorithms based on Chirp-Z transform is the most widely used. Based on theexisting literatures, the paper sorts out the main formula of many articles and gives detailderivation. In the following, the paper gives the simulation of point target and plane target viaMATLAB language and achieves good imaging effect. After discussing the three types of algorithms, the advantages and disadvantages of them are compared.Finally, a study is made on deramp processing, which could also overcome spectralaliasing. Compared to azimuth filtering processing, the computation is reduced by about15%and thus the imaging efficiency is improved significantly. Based on the fourth chapter, anefficient two-step imaging algorithm based on azimuth deramp is presented. The simulationresult via MATLAB shows the validity of the presented algorithm.In the end, the main work of the paper is summarized and the future work is prospected.