Extension of Bistatic SAR Processing Techniques: Steps to an Interferometric Bistatic Processor

Kurzfassung

Notable efforts have been dedicated in the recent past to the analysis of bistatic SAR configurations; mainly because of their flexibility and performance, such configurations have become an attractive option in both airborne and spaceborne remote sensing. Since 2003, several bistatic airborne experiments have been carried out successfully to demonstrate their feasibility [1]. Moreover, different SAR processing algorithms have been presented to handle diverse bistatic configurations [2-10] both in time and frequency domains, providing good imaging capabilities. However, bistatic SAR imaging strategies still suffer in a general way from inherent weaknesses when compared to monostatic SAR [12-13]. Errors introduced by different clocks in transmitter and receiver [11] and the orography dependence of the focussing functions in the general bistatic case make the development of phase preserving bistatic processors a challenging task. These errors introduce both phase and position inaccuracies in the processed images, whose impact is of special importance for interferometric SAR systems which rely significantly on the precision of the bistatic SAR processor. On the other hand, height information obtained by exploiting the vertical offset of both transmitter and receiver in the interferometric processing could be used iteratively to progressively reduce intrinsic processing errors due to the orography within the imaged scene. The impact of the full 3D behaviour of bistatic SAR processing, a limitation in itself, can be minimised by properly estimating the scene geometry using the interferogram. This paper addresses the potentials and challenges of interferometric processing of airborne bistatic SAR data. Furthermore, compensation strategies to reduce motion, orography and clock errors will be presented. Geometry correction strategies to account for position errors due to synchronisation are also adressed. The interferometric bistatic data are used to generate a DEM of the imaged scene, which feeds back the geometry estimator of the bistatic SAR processor to recursively improve focussing. A detailed analysis of the performance improvement will be presented for different realistic interferometric scenarios, showing the precision requirements for the compensation algorithms. The improvements for the case of airborne bistatic systems are demonstrated by an interferometric processing of actual data of the DLR-ONERA joint bistatic campaign.