Detection, location and imaging of fast moving targets using multi-frequency antenna array SAR

Detection, location and SAR imaging of moving targets in clutter have attracted much attention. Locations of moving targets in the SAR image are determined not only by their geometric locations but also by their velocities that cause their SAR images de-focused, smeared, and mis-located in the azimuth dimension. Furthermore, the clutters may cause the detection of moving targets more difficult. Several antenna array based algorithms have been proposed to re-locate the moving targets in the SAR image. With a linear antenna array, the clutters may be suppressed using multiple phase centers. However, there are only two parameters involved in a linear antenna array, i.e., number of receiving antennas and the distance between two adjacent antennas. These two parameters physically limit the capability to detect the accurate locations of fast moving targets and such as vehicles, and only slowly moving targets, such as walking people, can be correctly re-located. In this paper, we propose an antenna array approach where transmitting single wavelength signals are generalized to transmitting multiple wavelength signals (called multi-frequency antenna array SAR). We show that, using multi-frequency antenna array SAR, not only the clutters can be suppressed but also locations of both slow and fast moving targets can be accurately estimated. Far example, using two-frequency antenna array SAR system with wavelengths lambda(1) = 0.03 m and lambda(2) = 0.05 m, the maximal moving target velocity in the range direction is 15 mls while using single frequency antenna array SAR system with wave length lambda(1)=0.03 m or lambda(2) =0.05 m, the maximal moving target velocity in the range direction are 3m/s or 5m/s, respectively. A robust Chinese Remainder Theorem (CRT) is developed and used for the location of fast and slowly moving targets. Simulations of SAR imaging of ground moving targets are presented to illustrate the effectiveness of the multifrequency antenna array SAR imaging algorithm.