Moving Targets Parameters Fast Estimation Techniques In SAR-GMTI System

Radar technology utilizing microwave carrier provides the advantages of all-time, all-weather and long range work. As one of the most important radar applications, ground moving targets indication (GMTI) can detect the ground moving targets, which is the necessary prerequisite of moving targets tracking and recognition. Combined GMTI with synthetic aperture radar (SAR) technology, SAR-GMTI can detect the moving target when imaging the scenario, and can provide moving target localization in the SAR image, enhancing the information of the moving targets, which is valuable in both civil and military applications.In the process of SAR-GMTI, moving targets motion parameters not only cause severe blurring of the moving target imaging, which go against to moving targets recognition, but also degrades the target detection and localization performance. Moreover, motion parameters play an important role in moving targets tracking and classification. For the requirement of motion parameters estimation, moving targets radial velocity estimation is confronted with ambiguous estimation by phase-based method and huge complexity computation by amplitude-based method, while azimuth velocity fast estimation is mainly prevented by huge complexity computation load due to parameters searching, which cannot meet the high real-time requirement of the modern SAR-GMTI system. Thus, it is significant to study motion parameters fast estimation technologies.In order to solve these problems, we summarized our main work as follows:1. Focusing on the ambiguous radial velocity estimation of the along track interferometry phase based method, we have proposed a new approach based on dual-channel interferometric phase of range frequency to resolve ambiguity of radial velocity, which utilizes the multiple wavelength corresponding range frequency. Firstly, the linear relationship between interferometric phase and range frequency is obtained. And the slope of interferometric phase respect to range frequency is utilized to estimate the radial velocity unambiguously. Since the slope of the ambiguous phase and the range frequency equals to that of the unambiguous case when the difference of the neighboring phases corresponding the range frequencies is less than π, i.e. the phase wrapping has no effect on the slope, the proposed method possesses the advantage of being independent of wrapped phase. Because the phase wrapping has no effect on the slope aforementioned, the proposed method is independent of wrapped phase. Combined with the displaced phase center antenna technology, the proposed method can be applied in clutter background. Experiment results demonstrate the effectiveness of the proposed method.2. In order to solve the radial velocity ambiguous estimation problem, we propose a Doppler based phase method using a single channel to estimate the radial velocity of ground moving targets unambiguously. In the synthetic aperture time, the constant radial velocity results in constant Doppler centroid displaced for moving target in different observing angles, i.e. the Doppler based phase is changed constantly as radial velocity, and the slope between the phase and Doppler frequency can be used to estimate the radial velocity. Two-look operation in the range frequency domain and interferometry in the Doppler domain are done to keep the interferometry phase meet the assumption of phase continuity. The lease squares linear fitting is used to estimate the slope between interferometric phase and Doppler frequency, and the radial velocity can be calculated by the slope. Since the separable conditions of the multiple moving targets in the range compression domain, in the Doppler domain and in the range frequency-Doppler domain have been presented, the proposed method can be used for multiple moving targets to estimate the radial velocity, respectively. The proposed method possesses not only good real-time performance but also the capability of estimating the radial velocities of multiple moving targets simultaneously in the Doppler domain, which is very practical in modern SAR-GMTI systems. Simulation and experimental results validate the proposed method.3. To solve the problems, huge complexity computation and compromise selection of searching step size, of the amplitude-based (Radon transform) estimation method, an Radon transform (RT) based fast estimation is proposed to estimate the radial velocity of fast moving target. By exploring the geometry information of the moving target in the Radon domain, the geometry relationship between the RT angles and the moving targets range walk angle can be modeled, and then the proposed RT method can calculate rather than searching the radial velocity of moving target unambiguously. By utilizing the geometry information, the proposed method simplifies the conventional range and angles (2-D) searching procedure into several times range (1-D) searching procedure efficiently, so the huge complexity computation has been reduced and the compromise selection of the searching step size has also been avoided. In order to apply the efficient RT estimation method in the real scenarios with clutter, noise and estimation error, we exploit the geometry information in the RT domain further, and the robust methods, clutter suppression Radon transform (CSRT), noise background Radon transform (NBRT) and angle learning Radon transform (ALRT) are proposed from new viewpoint. These robust methods are unified together as URT method to obtain a method possessing all of the properties, to keep the URT method can be used in the real scenarios. The theoretical and experimental analysis provides qualitative and quantitative evaluations into the effectiveness of the proposed methods, and the URT method performs much better in the real data processing.4. We turn our focus on the moving targets azimuth velocity and Doppler chirp rate estimation in this part, and an fractional Fourier transform (FRFT) based method has been proposed to realize parameters fast estimation. By analyzing the edge of the mismatched results, we find that there exists some function representing the edge, and the optimization of the edge function is related to the azimuth velocity and Doppler chirp rate of the moving target. Twice FRFT can cancel the constant term in the edge function, and the relationship between the FRFT angles and the time-frequency angle of the moving target can be obtained, then the azimuth velocity and Doppler chirp rate can be estimated by the calculated time-frequency angle. Since only twice FRFT is done to estimate the parameters, the proposed FRFT method possesses much lower complexity computation and much better real-time performance. Focusing on the case of azimuth sampling rate lower than the Nyquist rate, we proposed efficient compressed sensing (CS) method to realize the moving target sparse imaging. The proposed method utilizes the concept the proposed FRFT fast estimation method, and triple CS recovery can image the moving target sparsely. Simulations and real data process are provided to demonstrate the effectiveness of the proposed methods.