The TerraSAR-X Multi-Mode SAR Processor - Algorithms and Design

TerraSAR-X is a national German satellite mission deploying a high resolution active phased array X-band SAR instrument into orbit in 2005. The configuration and parameterization of the instrument is highly flexible enabling StripMap, ScanSAR and SpotLight imaging modes in various polarizations in a wide range of different antenna beams. A special dual receive antenna mode will even provide the possibility for along track interferometry. The mission will be conducted by the German Aerospace Center DLR. The principle tasks of the ground segment are satellite commanding, SAR data reception and archiving, SAR data processing and distribution. The main item of the payload related part of the ground segment will be the new TerraSAR-X multi-mode SAR processor TMSP which adequately fits to the TerraSAR-X instruments flexibility. The TMSP design and selection of algorithms are mainly driven by the requirements, that all SAR raw data will be systematically analyzed, archived and focused in order to obtain medium resolution browse images for cataloguing. Further on, high precision phase preserving complex images as well as highly accurate multilook and geo-referenced images will be processed on user request. The effort of validation and the maintainability of the TMSP software are also taken into account for the system design. The finally developed algorithm for the TMSP is based on Chirp and Azimuth Scaling, SPECAN and Subaperture Processing. Therefore the already existing algorithms Chirp Scaling and Extended Chirp Scaling with Subaperture Processing which are optimal for the individual imaging modes have been analyzed and decomposed into their principal signal processing steps. Those which can be used commonly have been identified and rearranged, while mode specific steps lead to branches in the algorithm. Since the commonly required signal processing steps have to be implemented, tested, documented and validated only once, the resulting software gets more coherent and inexpensive than three individual mode specific SAR processors.