Modeling and high-precision processing of the azimuth shift variation for spaceborne HRWS SAR

One basic assumption for high-efficient SAR imaging algorithms is azimuth-shift-invariance of SAR data. The new spaceborne high-resolution wide-swath (HRWS) SAR generation will retain the same significant swath depth of the past but will achieve much higher resolution. The formerly insignificant variance of effective radar velocity along azimuth path will cause noticeable focusing blurring at azimuth scene edges. It is a new problem to accommodate the azimuth-shift variance with high efficiency and high precision. In this paper, the azimuth variation of effective velocity and main influencing factors are analyzed and accurately modeled. A highly accurate and efficient phase preserving processor with embedded azimuth variance compensation for sliding spotlight mode is proposed. The proposed processor does not add extra computing load and inherits the high efficiency of the original azimuth-invariant subaperture approach. Through careful design of the fourth-order phase terms of the processing functions, azimuth variation compensation can be achieved in company with the original baseband azimuth scaling steps. Simulation with point targets in C-band HRWS sliding spotlight mode is made to validate the focusing and phase preservation performance of the proposed algorithm.