Investigation Of ISAR Motion Compensation And InSAR Interferometric Calibration Technology

The imaging radars based on synthetic aperture technique have the capability of getting high resolution images of targets day and night in all weather from long range, so they have potential applications in both civilian and military areas. In an inverse synthetic aperture radar (ISAR) system, the primary problem is to estimate the target's translational motion component precisely, and then to rebuilt a high quality image by motion compensation. In an interferometric synthetic aperture radar (InSAR) system, the accuracy of interferometric parameters plays an important role in the procedure of digital elevation model (DEM) reconstruction. So locating ground calibrators is needed to calibrate the interferometric parameters and improve the accuracy of DEM reconstruction. In this background, this paper focused on the research of ISAR motion compensation and InSAR interferometric calibration.At first, the research of ISAR motion compensation was proposed, which included range alignment and phase compensation. In ISAR range alignment, a modified technique based on bary centre method and gradient descent algorithm is developed in this paper. The algorithm is implemented in two steps. The bary centre method is used to get a coarse result in the first step. In the second step, the gradient vector of the energy function in the frequency domain is calculated, and gradient descent search algorithm is used to achieve an accurate global range alignment quickly. Then, in order to decrease the influence of heavy target scintillation, an improvement of range alignment method based on the quadratic polynomial fitting is presented. The shifts made to the echoes were modeled as a polynomial in this method, and the coefficients of this polynomial are got from the envelope correlation information. This technique is robust against noise and target scintillation. In the research of phase compensation, a novel method based on improved discrete chirp-fourier transform (DCFT) is proposed for ISAR phase compensation. It modeled the phase function as a chirp signal, and used the DCFT algorithm which benefits from FFT method to find the function of phase errors quickly, then used the minimum entropy method in a short space to do a further phase compensation, so both of the efficiency and the accuracy in the compensation were kept. And the simulated results showed the advantages of the range alignment and phase compensation method presented above. In the research of the interferometric calibration for InSAR system, because the traditional interferometric calibration methods often suffer much from the morbidity of the sensitivity matrix, a novel interferometric calibration method based on genetic algorithm (GA) was proposed in this paper. The method used genetic algorithm to rectify the interferometric parameters, which can avoid the inverse calculation of morbid matrix, and can also improve the precision and stabilization of the interferometric calibration. The simulation results showed the validity and stabilization of the proposed algorithm.