Performance analysis of a hybrid bistatic SAR system operating in the double sliding spotlight mode

A bistatic synthetic aperture radar uses a separated transmitter and receiver flying on different platforms to achieve benefits like exploitation of additional information contained in the bistatic reflectivity of targets, reduced vulnerability for military applications, forward looking SAR imaging or increased RCS. A particular constellation, where the transmitter is in space and the receiver near or on the earth surface (e.g. aircraft, tower) is called a hybrid bistatic SAR system. Besides technical challenges, like the synchronization of transmitter and receiver, the overlap of the two antenna footprints is of vital importance. Due to the extreme platform velocity differences, SAR modes with flexible steering of the antenna beams are necessary. The sliding spotlight mode offers such a beam steering, where the antenna footprint velocity can be chosen slower or faster than the platform velocity. If both transmitter and receiver use this mode it is called double sliding spotlight mode, which will be investigated in this paper using the example of the satellite TerraSAR-X and the airborne SAR system PAMIR. Several aspects like the ground resolution, Doppler frequency and Doppler-bandwidth will be analyzed.