Azimuth-invariant, bistatic airborne SAR processing strategies based on monostatic algorithms

Abstract

Bistatic configurations have awakened a great deal of interest in the recent past among the SAR research community for both airborne and spaceborne sensing. However, bistatic SAR campaigns remain a technical challenge. In this context, current experiments are helping to understand real engineering problems concerning bistatic SAR data acquisitions. In February 2003, DLR and ONERA carried out successfully [1] one of the very first bistatic airborne campaigns. The E-SAR and RAMSES systems were flown in two basic geometrical configurations, both involving parallel flights at the same speed: one defined by along-track acquisitions and the other by across-track acquisitions. These bistatic configurations share with monostatic SAR the invariancy in the along-track dimension, which allows and suggests the using of Doppler domain focussing techniques. This paper puts forward an extension of airborne SAR monostatic focussing algorithms to the azimuth-invariant, bistatic case. A derivation of the point response in range-Doppler domain is presented; the differences between azimuth-invariant, bistatic and monostatic point responses are outlined. Using these results, bistatic focussing solutions based on range-Doppler (RD) [2] and extended chirp scaling (ECS) [3] algorithms are analysed. Particular implementation problems, like Doppler parameter estimation and bistatic motion compensation [4] strategies are also presented. Finally, the algorithms are tested with real data from the DLR-ONERA bistatic airborne campaign.