Research On Technologies Of Moving Targets Imaging In Distributed SAR

Distributed small satellite SAR is a new radar implementation, which is consisted of many several satellite worked cooperatively. Distributed satellite SAR can achieve more high resolution image through spectrum fusion, improve moving targets detection probability and reconstruct three dimensions terrain by InSAR interferometric technology. Small spaceborne system can work all-weather and all-day, which is a strong advantage in military or civil field.In this dissertation, moving targets imaging process in distributed small satellite SAR is proposed firstly. Based on the signal formation established in this paper, the features of moving targets signals is researched and analysis. The research of multi-satellite sample and its signal reconstruction method can provide the theory foundation for moving targets imaging and focusing.The signal received from multiple SAR has spectrum deviation, but moving targets could change the deviation formation. Hence it can not determine the moving target echo signal spectrum shift from the baseline relationship. A method estimated spectrum shift from the instantaneous frequency of the interferometric phase fringe in distributed SAR moving target signal is proposed. The method not only has high precision of estimation, but also broke the prior knowledge of the distributed configuration and the baseline. After obtained the frequency offset in the SAR moving target signal, we can integer the spectrum, to extend the target signal spectrum to improve the resolution of moving targets imaging.Target motion changing the Doppler parameters leads to azimuth compression failure, which called the image defocus performance. The traditional idea of focusing moving targets is estimating the parameters of moving target to adjust the azimuth compression function to finish moving target focusing. After studies the moving target defocusing phase error existing in the defocus image data, a method focusing moving target through spectral decomposition of the defocus image data to achieve the phase correction function to completed focusing is proposed. The method avoids the estimation of moving target parameters which accumulating errors and improve focus efficiency as well as the quality of the focusing. Through signal processing techniques, distributed SAR can improve the imaging resolution, but the image quality will be reduced when the targets closed each other. In this regard, the proposed spectrum estimation method using amplitude and phase estimation signal instead of the traditional FFT spectrum, and extended it to estimate the spectrum of distributed SAR fusion signal based on InSAR interferometry. The method can improve the spectral resolution and lower sid elobes, thereby eliminating interference between targets and further improve image quality.