| Synthetic Aperture Radar (SAR) is a kind of all-time, all-weather imaging radar with high resolutions. It is widely used in earth remote sensing, marine research, resources exploration, disaster forecasting, military reconnaissance and other fields. The spotlight SAR can offer better azimuth resolution by steering the radar antenna beam to illuminate the same area on ground, which provides a long illumination time for the observed scean. It overcomes the azimuth resolution restriction of the stripmap mode SAR and provides a great potential for ground targets detection and identification.Based on the charactersistic of Spotlight SAR echo signal, the image algorithms and the motion compensation methods are discussed, and the corresponding simulation analysis are completed. The study of this dissertation includes the following three aspects:(1).The dechirp technology commonly used in spotlight SAR data receiving and the echo characteristics on the condition of three data receiving mode are discussed. The comparision of the spotlight SAR and the stripmap mode SAR is given.(2).An imaging algorithm based on CZT is derived in detail after the disscusion of the polar format algorithm and frequency scaling algorithm. Finally a comparation of these three algorithms is given.(3).The traditional motion compensation method is studied after analyzing the reasons and the imapacts of the motion error. Finally considered the high resolution characteristics of the spotlight SAR, an improved motion compensation method is proposed. The validity of the method is verified by the simulation results.In summary, this dissertation not only analyses the Spotlight SAR signal characteristics, but also investigates the high-resolution algorithms and motion compensation methods. A polar format algorithm based on ChirpZ transform and a improved motion compensation algorithm are derived. The simulation results show the feasibility and effectiveness of the algorithms. |
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