Research On Multibeam SAR Imaging And Moving Target Detection

The synthetic aperture radar(SAR)strives to achieve high resolution and wide swath images at the same time.However,it is a challenging problem for single antenna synthetic aperture radar to realize high resolution and wide swath images simultaneously on account of the limitation of minimum antenna area.To overcome this problem,multiple beams SAR system has been employed,which increasingly attracts the attention of scholars all over the word,especially,the displaced phase center multiple azimuthal beams(DPC-MAB)SAR system.In addition,moving targets are the significant focus of the observation scene in the field of military and traffic monitoring.It has much practical meaning to study how to detect moving targets in the high resolution and wide swath scene.Therefore,this paper studies multiple beams SAR imaging and moving target detection based on the spaceborne platform.The primary contents of this paper are as follows:The limitation of minimum antenna area is deduced on the basis of the traditional single antenna SAR system model to make sure that the system can't realize high resolution and wide swath images simultaneously.This paper introduces multiple beams SAR of various working modes briefly,analyses the signal processing of DPC-MAB SAR system,which is taken as the research focus.Based on the DPC-MAB SAR system,this paper studies the effects of azimuthal non-uniform sampling.The azimuthal non-uniform sampling signal is reconstructed by using the filter group algorithm,the A-matrix algorithm and the improved A-matrix algorithm to realize high resolution and wide swath imaging unambiguously.The validities of the algorithms are proved by the experiments.Besides,the computational complexities of the algorithms are compared.Based on the DPC-MAB SAR system,the impacts of target motion parameters on the SAR imaging are analyzed theoretically.It is pointed out that the radial motion leads to a periodical phase error existing in the reconstructed azimuth signal.The DPCA technology,ATI technology and DPCA-ATI technology are applied to the moving target detection of DPC-MAB SAR system and the simulation verification and algorithm performance comparison are carried out.Besides,the known radial velocity of moving target can be utilized to correct the periodical phase error effectively.The key to correct the above phase error is accurate radial velocity estimation.Firstly,the echo data of adjacent antennas interferometry approach is employed to estimate the radial velocity.In order to improve the performance of radial velocity estimation,this paper puts forward a fast search algorithm based on multi-resolution and gradient dichotomy,as well as,the under-sampling fractional Fourier transform and the fractional Fourier transform with a periodical phase error are proposed.Then,this paper combines the Doppler centroid ambiguity estimation to obtain the unambiguous radial velocity.The simulation verification and performance analysis of the algorithms are carried out.