Research On High Resolution Radar Imaging Method Of Ship Target Under Moving Platform

Ship targets are a type of target that has attracted much attention in maritime law enforcement and military activities,and radar imaging technology is one of the most effective methods for detection and reconnaissance of ship targets.Synthetic Aperture Radar(SAR)can perform high-resolution imaging of targets in all weather conditions.Compared with the traditional broadside SAR imaging,the high-squint SAR can detect the front target in advance and flexibly change the observation angle.Inverse Synthetic Aperture Radar(ISAR)can obtain richer information and high-resolution images by controlling the beam pointing and continuously illuminating the target of interest.In addition,ISAR imaging technology can compensate for the non-cooperative motion of the ship target,and even actively use the swing of the ship target itself to form a high Doppler resolution.High-resolution imaging methods for maritime ship targets that comprehensively utilizes high-squint SAR and ISAR technologies can enhance information acquisition ability.However,there are several difficulties and pain points to be solved.Firstly,the existing research on high-squint SAR imaging algorithms mainly focuses on imaging stationary targets.As we all know,the ship target at sea is a non-cooperative target with complex motion,which is mainly reflected in its three-dimensional translation and three-axis swing relative to the radar platform.Therefore,the direct use of the traditional algorithms will make the ship target appear serious defocus;secondly,in practical application scenarios,due to unfavorable factors such as long-distance detection,limited transmit power,small target Radar Cross Section(RCS)or strong noise interference,the signal received by the radar is relatively weak,and the Signal-to-Noise Ratio(SNR)of the echo is usually low,which not only causes a lot of noise in the radar image,but also reduces the accuracy of the ISAR motion compensation,further resulting in defocusing of the radar image;finally,there may be micro-motion parts on the ship such as mechanically rotating antennas,propellers,etc.The periodic micro-motion of these components will cause Micro-Doppler(MD)interference bands in the ISAR imaging results,reducing the readability of radar images.These problems bring challenges to the acquisition of high-resolution radar images of ship targets,which are not conducive to the subsequent target recognition work.To solve these problems,the main research contents of this dissertation are as follows:1.Research on the method for high-squint SAR imaging of maritime ship target.This research is based on combining the basic theory of high-squint SAR and the characteristics of ship target movement.In the above,the theoretical analysis of the Doppler component produced by the motion of the ship target is carried out.In this dissertation,the problem of residual range walk,Third Range Compression(TRC),and the problem of additional azimuth chirp rate are theoretically analyzed.On the basis of theoretical analysis,a high-squint SAR imaging method of ship target is proposed.It mainly includes high-squint SAR range-azimuth decoupling and coarse imaging,ship target interception,equivalent ISAR data inversion mapping,and ship target refocusing based on ISAR techniques.Aiming at the refocusing of ship targets,this method makes use of ISAR technology to compensate for the non-cooperative motion of ship targets.Furthermore,this dissertation proposes a "WASH-CLEAN"(WAter SHed and CLEAN,WASH-CLEAN)algorithm that combines the characteristics of watershed algorithm and CLEAN algorithm.The experimental results verify the correctness of the analyzed theory and the effectiveness of the proposed method.2.Research on ship target radar imaging method under low SNR environments.This dissertation proposes a Similarity-Oriented(SO)denoising framework for high-resolution imaging of ship targets under low SNR environments.This framework bases on Low-Rank Matrix Approximation(LRMA)technique and adopts domain/step denoising stategy.This framework includes a RAnge Profile Similarity-Oriented(RAP-SO)denoising method designed for High-Resolution Range Profile(HRRP)matrix,and a PIx El Similarity-Oriented(PIE-SO)denoising method designed for the radar Range-Doppler(RD)image.Ultimately,the accuracy of motion compensation is improved,thereby improving imaging quality while addressing both the symptoms and the root causes.The simulated and the real measured data imaging results verify the effectiveness of the proposed method.3.Research on ship target radar imaging method with the the MD interference.This dissertation focuses on the separation technology of target rigid body and MD based on Robust Principal Component Analysis(RPCA).This study is carried out from two dimensions of radar HRRP matrix domain and RD image domain,respectively.For HRRP matrix domain,joint constrained RPCA is proposed.For RD image domain,the low-rank property of MD matrix is theoretically analyzed.Then,based on the sparsity of target rigid body components and the low-rank property of MD components,an RPCA algorithm based on radar RD images is proposed for MD separation.After MD separation,the readability of the radar image is improved,and the separated target rigid body components and MD components can provide information for subsequent target recognition.The simulated data processing results verify the effectiveness of the proposed method.