A Study Of SAR-GMTI System Detection Performance

The Synthetic Aperture Radar-Ground Moving Target Indication(SAR-GMTI) system can not only form high resolution image in two dimension of the observation scenes,but also detect the moving targets in it,which is why this system is widely used in both civilian and military field. This paper focuses on the detection performance of SAR-GMTI system, and the various factors that affect the detection performance are analyzed. Then we propose an improved method to decrease the adverse defocusing effect of moving targets on the system. The detection and parameter estimation performance are not good due to its low degree of freedom for the SAR-GMTI system, while by simultaneously transmitting and receiving signals mutually orthogonal using multi-antennas,the MIMO radar can achieve far more numbers of degree of freedom than the sum of transmitting and receiving antennas. We can dramatically improve the image resolution and detection performance of SAR-GMTI system based on the property of high DOF of MIMO-SAR GMTI system.Our works are summarized in details as follows.First, we study the detection probability calculation process of SAR-GMTI system, and different factors involved in different calculation aspects are analyzed, respectively, and then indicate their impacts on the detection performance.Second, we analyze the defocusing effect of moving targets. Because of the existence of the moving target’s velocity, its image appears defocused, and this may lead to the dispersion of energy and a decrease in SNR, which is not conducive to detect moving targets. In order to eliminate this adverse effects caused by defocus, the traditional methods of Phase Gradient Autofocus(PGA) and the minimum entropy are introduced. Both methods can concentrate energy and increase SCNR, which can improve the detection performance. We also analyze the performance of the two methods.Third, we study the signal processing of the MIMO-SAR GMTI system. The combination of MIMO technology and SAR system can not only solve the contradiction inherent in the SAR system between high resolution and wideobservation scene, but also achieve a better system detection performance. Narrowband signals with different carrier frequencies are transmitted by MIMO-SAR system, and then the spectrums of the signals are superimposed to synthesize a large bandwidth signal, which can increase the range resolution. Because the DOF of the MIMO-SAR GMTI system is higher than that of SAR-GMTI system, the MIMO-SAR GMTI system can detect slower and weaker targets. In this paper, a complete scheme of data process regarding MIMO-SAR GMTI system is proposed, and due to the reason that different carrier frequencies correspond to different ranges of detectable speed, the problems of velocity ambiguity and blind speed can be solved, which leads to more accurate estimation of moving target parameters.