Current advanced spaceborne synthetic aperture radar (SAR) systems may operate at multiple imaging modes, including conventional modes as stripmap, ScanSAR and spotlight, as well as the state-of-the-art SAR modes, e.g., sliding spotlight, TOPS (Terrain Observation by Progressive Scans) and inverse TOPS, etc. A novel image formation scheme for unified processing spaceborne SAR data was proposed, which significantly simplified complexity of SAR processor sub-system. The unified-model-coefficient (UMC) was defined for modeling all SAR modes by means of analyzing both imaging geometry and time-frequency diagram corresponding to each imaging mode, respectively. The unified mathematical formula for modeling all SAR modes echo signal was derived as a function of UMC. Consequently, a unified image formation scheme for accurately focusing spaceborne SAR data in an arbitrary mode was proposed, which integrates all of SAR image formation procedures into a standard three-step processing framework, namely, de-rotation, data focusing and re-sampling, which evidently improve efficiency and robustness of data processing sub-system. Computer simulation experiment results verify the effectiveness of the proposed scheme.
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