Estimation of along-track velocity of road vehicles in SAR data

At the German Aerospace Center, DLR, an automatic and operational traffic processor for the TerraSAR-X ground segment is currently under development. The processor comprises the detection of moving objects on ground, their correct assignment to the road network, and the estimation of their velocities. Since traffic flow parameters are required for describing dynamics and efficiency of transportation, the estimation of the velocity of detected ground moving vehicles is an important task in traffic research science. In this paper we show for TerraSAR-X simulated data how the along-track velocity component of a moving vehicle can be derived indirectly by processing SAR data with varying frequency modulation (FM) rates and exploiting the specific behavior of the vehicle's signal through the FM rate space. An airborne ATI-SAR campaign with DLR's ESAR sensor has been conducted in April 2004 in order to investigate the different effects of ground moving objects on SAR data and to acquire a data basis for algorithm development and validation. Several test cars equipped with GPS sensors as well as vehicles of opportunity on motorways with unknown velocities were imaged with the radar under different conditions. To acquire reference data of superior quality, all vehicles were simultaneously imaged by an optical sensor on the same aircraft allowing their velocity estimation from sequences of images. The paper concentrates on the estimation of along-track velocities of moving vehicles from SAR data. Velocity measurements of vehicles in controlled experiments are presented, including data processing, comparison with GPS and optical reference data and error analysis.