Time-reversal-based multipath mitigation technique for entropy minimization of SAR images

Synthetic Aperture Radar (SAR) images a target region reflectivity function in the multi-dimensional spatial domain of range and cross-range with a finer azimuth resolution than the one provided by any on-board real antenna. Conventional SAR techniques just consider a single reflection of transmitted waveforms from targets. Nevertheless, today´s new applications force SAR systems to work in much more complex scenes such as urban environments. Consequently, multiple- bounce returns are additionally superposed to direct-scatter echoes. We refer to these as ghost images, since they obscure true target image and lead to poor resolution. By applying Time Reversal concept to SAR imaging (TR-SAR), it is possible to reduce considerably -or even mitigate-ghosting artifacts, recovering the lost resolution due to multipath propagation. Furthermore, some focusing indicators such as entropy (E), contrast (C) and Rényi entropy (RE) provide us with a good focusing criterion when using TR-SAR.