Moving Target Detection And Imaging For SAR With New Multi-Band/Multi-Waveform System Configurations

The synthetic aperture radar(SAR) possesses the capability of long operating distance, wide swath, and could obtain 2-D high resolution images operate under all the meteorological conditions. With the combination of SAR and ground moving target indication(GMTI) technology, the SAR-GMTI system not only could obtain high resolution image, but also could identify the moving targets, which is of great use for ground surveillance, situation evaluation, as well as for optimal decision making. Therefore, the SAR-GMTI is playing a more and more important role in battlefield surveillance, military reconnaissance and ground transportation control etc. However, traditional SAR-GMTI technologies are well developed for linear frequency modulated pulse in single-band single-channel or multi-channel system. To satisfy various demand in military and civil applications, such as target detection and jamming suppression, etc., advanced SAR-GMTI system with new system configurations and modes are emerging. Subsequently, under new system configurations, the system design, transmitting waveform and signal processing techniques are not the same with traditional SAR system, and thus it will face new challenges and problems. Some crucial practical problems would appear under new system configurations. This dissertation is dedicated to research on detection and imaging of moving target under various SAR system configurations, such as single-channel multi-band, using linear frequency modulated continues wave or using frequency diverse array. The content of the dissertation is listed as follows:1. First, basic principles of SAR-GMTI are introduced. For SAR system, several classical operation modes and their corresponding advantages are analyzed. Then, the signal model for three-channel moving target is presented. Theoretical derivations and experimental simulation are provided to illustrate the imaging methodology for the stationary and moving targets. Moreover, the azimuth Dechirp method for moving target imaging is also investigated. Further, several frequently used methods including the detailed processing steps for multi-channel SAR-GMTI are described, which provides theoretical foundation for the following analysis.2. To deal with the existing issues of GMTI in single-channel SAR or multi-channel SAR, a novel GMTI approach was proposed for multi-band single-channel SAR. Under the multi-band single-channel SAR system configuration, the geometrical model and the clutter suppression method are presented. Moreover, efficient methods for moving target detection, motion parameter estimation, imaging and localization are presented. To deal with the issue of velocity blind zone, a nonlinear optimization problem was put forward. Then, this optimization problem is solved by optimizing the system parameters based on the genetic algorithm. The optimal choice of system parameters could greatly narrow down the detectable velocity blind zone, and increase the detectable velocity of the moving target, which is of great help for the frequency band utilization and moving target detection.3. For frequency modulated continuous wave(FMCW) SAR, fast moving target would result in relatively large range migration and spectrum split, which would defocus the image or lead to the appearance of ghost targets. This would decrease the signal-to-noise ratio(SNR), and thus would poses a hindrance for target detection. To tackle this issue, a novel algorithm was proposed. First, the principles and characteristics of FMCW SAR are introduced. By constructing the geometrical model for SAR-GMTI, the radar received echoes of moving target are analyzed. Then, moving target indication and coarse imaging results are realized by incorporating the Doppler shift compensation and displaced phase center antenna(DPCA). Moreover, to deal with the Doppler spectrum split problem without knowing the motion parameters, an efficient imaging algorithm was proposed by combining the Doppler shift compensation, azimuth deramp, Keystone transformation, ambiguity number estimation. This could greatly increase the SNR and detection possibility, and could obtain well-focused imaging result for multiple targets sharing equivalent ambiguity number. Finally, the experimental results prove the effectiveness of the proposed algorithm.4. For traditional SAR-GMTI, the influence of stationary clutter is often considered and well-processed. However, in some military cases, there exists deception jamming signals in the radar echoes, which would also degrade the GMTI performance significantly. To mitigate the adverse impact of deception jamming, a novel SAR-GMTI method utilizing the frequency diverse array(FDA) was proposed. First, the FDA models for common radar and SAR are discussed, and followed by presenting the image formation principles for FDA-SAR. Then, by analyzing the 2-D distribution property of the range-angle domain and making full use of the range, angle and spatial angle information of echo signal, the deception jamming could be suppressed. Hence, a clean image could be obtained without introducing too much signal loss and imaging quality degradation. By incorporating the DPCA into the FDA-SAR, the clutter suppression could be realized successively. Finally, the experimental results prove that the proposed algorithm could obtain satisfactory result even with the presence of deception jamming.