An Airborne SAR Experiment For Ground Moving Target Identification

Abstract

With the launch of the advanced high resolution radar satellite TerraSAR-X in summer 2006 new possibilities open to demonstrate traffic monitoring from space. At the German Aerospace Center an automatic and operational traffic processor is developed for the TerraSAR-X ground segment. This comprises the detection of moving objects in Synthetic Aperture Radar (SAR) images, their correct assignment to the road network and the estimation of their velocities. An airborne SAR campaign with DLR’s ESAR sensor was flown in an Along Track Interferometry (ATI) mode in April 2004 to investigate the effects of ground moving objects on SAR data and to acquire a data basis for algorithm development and validation for the traffic processor. Several vehicles with measured GPS tracks as well as vehicles on motorways with unknown velocities were imaged with the radar under different conditions. The paper provides an overview on the flight campaign and on the used experiment setups. Several data takes with different platform headings were acquired over a test site including controlled cars on a runway and over other test sites including motorways. The across track velocity was estimated by means of ATI phase. The measurements for experimental and road vehicles are presented, including comparison with GPS and optical reference data. To optimize the detectability of moving objects and to facilitate accurate speed measurements, adapted SAR processing approaches to compensate for energy losses because of a mismatched processed Doppler Centroid (due to across track motion) and because of defocused impulse responses (due to along track motion) were successfully applied to ESAR and SRTM data. Selected results and examples thereof are presented in the paper.