| Synthetic Aperture Radar (SAR), which has the characteristic of all-weather, day/night and long range, can enhance radar's information acquisition capability, especially the battlefield awareness ability, and has great value in both civilian and military applications.Ground Moving Target Indication (GMTI) and relocation is a necessary function of the SAR system, especially in military SAR application and signal processing. Comparing to single antenna SAR system, the multi-channel SAR-GMTI system with more spatial degree can utilize some advanced clutter suppression technologies to improve the signal to clutter plus noise ratio remarkably. Then the minimum detectable velocity and the relocation precision of the system are improved accordingly. In recent years, many countries in the world have been making great efforts to develop spaceborne and airborne multi-channel SAR-GMTI systems, study new GMTI theories and explore high efficient detection and location algorithms. However, there are lots of problems for GMTI with airborne or spaceborne radar system, for example, the blind velocity problem, the clutter suppression problem, the channel imbalance, the smear and azimuth displacement of moving target, the hybrid baseline influence. The primary contributions of this dissertation, which is devoted to the above aspects, are summarized as below:1. In an Along Track Interferometric (ATI) SAR system, the length of the baseline shuold be big enough to acquire small minimum detectable velocity (MDV). However, long baseline will bring on more blind velocity and velocity ambiguity, which worsens the GMTI performance of the system. Basing on splitting the whole aperture into multiple sub-apertures in azimuth, we investigate the designing method of the optimum velocity response. The output signal-to-clutter-plus-noise ratio expression of the GMTI system is derived firstly, and then the way of designing optimum velocity response is presented.2. Basing on the analysis of the relationship between interferometric phase of the moving target and radar system parameters, the principle that system velocity response can be altered by the variation of wavelength and baseline is revealed. The proposed new method utilizes both multi-baseline and multi-frequency to unwrap the radial velocity and performs better than routine method. Synchronously, a numerical computation method is proposed to compute the ture radial velocity of the moving target, which is simpl but effective.3. For an airborne multi-channel SAR-GMTI system, there are differences among the frequency characteristic of two channels and the antenna patterns, which worsen the correlation of different SAR images. A new channel calibration method based on received ehcos is proposed to improve the correlation of the SAR images and then the clutter suppression ratio. Also, we combine the calibration method and the SPECAN (spectral analysis) algorithm to reduce the processing time of a tri-channel SAR-GMTI system.4. The method of estimating the along track velocities of multiple moving targets and imaging problem is investigated. By separating the multiple moving targets in SAR image domain, the signal to clutter plus noise ratio of the moving targets is improved, and the influence of different signal amplitudes on parameter estimation is also solved. The entropy of the refocused result is defined as the cost function to estimate the along track velocity. Comparing to the maximum magnitude decision, the new method is more robust.5. An unambiguous radial velocity estimation method of conventional airborne multi-channel SAR-GMTI system is proposed. By using the multiple signal classification (MUSIC) algorithm to improve the range resolution of the moving target image, the slightly low precision but unambiguous velocity can be obtained by polynomial fitting the range history of the moving target, which is used to solve the ambiguity of interferometric phase. Then the true radial velocity is estimated by the interferometric phase with known ambiguity time.6. Due to the hybrid baseline of the multi-channel SAR system, the interferometric phase changes with the target motion as well as the terrain height. Also, the correlation of the SAR images will be worsened by the hybrid baseline. The fluctuation of the interferometric phase worsens the performance of the clutter suppression and the radial velocity estimation process. In order to resolve this problem, a GMTI method with three steps is proposed. After two steps used to eliminate the local'flat earth'phase and the cross-track interferometric phase of the scene respectively, an adaptive filtering method is used to suppress the stationary clutter with the benefit of calibrating the sensor responses. Then, a conventional Constant False Alarm Rate (CFAR) detector can be used to indicate the moving targets. The validity of the proposed method is demonstrated with real data collected by an experimental airborne InSAR system.
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