Time-Frequency Signatures of a Moving Target in SAR Images

Moving targets within SAR scenes are distorted depending on the particulars of the target motion. For small motions, the uncompensated phase of a point reflector is a sum of a term proportional to the range component of the target motion, and a more complicated term depending on the azimuth motion. The resulting phase may be analysed with time-frequency techniques since the motion effect may alternatively be seen as a time dependent Doppler frequency. An experiment performed with a moving target within a scene collected by the German E-SAR system gave a signature that agrees well with theoretical predictions. Time-frequency analysis, using the smoothed pseudo Wigner-Ville method, gave a linear chirp with superimposed oscillations as predicted from the theory and the target motion.