Research On Airborne Sliding Spotlight Synthetic Aperture Radar Imaging

Synthetic aperture radar(SAR) is a microwave imaging system with many advantages, such as all weather, day/night, long distance and high resolution, which make it widely used in military and civil fields. As people continue to pursue the application of synthetic aperture radar technology on a variety of situations, different working mode SAR systems have been developed presently. The sliding spotlight mode is developed with the continuous development of SAR imaging technology, which combines the advantages of two kinds of traditional SAR modes: strip-map mode and spotlight mode. The sliding spotlight mode not only solves the problem of the limited imaging scene size on the spotlight mode, but also solves the problem of azimuth resolution on the strip-map mode. So it can find a good balance between the imaging scene size and the azimuth resolution and has more practical research value. Based on the above background, the main work of this paper is as follows:(1) We analyze the difference and connection between the strip-map mode and the spotlight mode and the sliding spotlight mode on the imaging geometry model, the azimuth Doppler frequency, the azimuth resolution and the range cell migration etc. And the advantages and disadvantages of the sliding spotlight mode are summarized, compared with strip-map mode and the spotlight mode. In addition, we analyze and establish the airborne sliding spotlight SAR imaging model. And the SAR echo equation is derived.(2) We analyze the traditional ?K imaging algorithm and research squint ?K algorithm to high squint imaging. In order to solve the problem of spectrum aliasing on sliding spotlight SAR imaging processing, we propose an azimuth scaling sub-aperture imaging algorithm based on ?K algorithm and method of dividing sub-aperture processing. In addition, we analyze detailed and derive sub-aperture partition criterion and propose corresponding sub-aperture partition method. Finally these algorithms are verified by the processing of the simulation data and the real data.(3) We research PGArope algorithm based on classical PGA and ROPE autofocusing algorithms. In order to the problem of long aperture motion error accumulation on the sliding spotlight mode, PGArope-MD sub-aperture autofocusing algorithm is researched based on the idea of dividing sub-aperture to reduce the error accumulation, and the algorithm principle is analyzed detailed. Finally, these algorithms are verified by the processing of the measured data.