Research On Bistatic SAR Moving Ship Target Imaging Methods

Bistatic Synthetic Aperture Radar(SAR)employs separate radar transmission and reception platforms,enabling the reception platform to capture all-weather and all-day high-resolution imaging of ground or sea scenes and targets.It not only has advantages such as good concealment and strong anti-interference ability,but also enables the receiver to work from side/forward/slant-looking,and has significant application value in the military and civilian fields.Bistatic SAR imaging of moving ship targets refers to the process of imaging ship targets with unknown motion states.It involves estimating the motion parameters or Doppler parameters of the ship target based on its bistatic SAR echo characteristics and patterns.This process aims to reconstruct the scattering characteristics of the ship target and obtain high-resolution images of the moving ship target using bistatic SAR.This dissertation focuses on theoretical research and method validation related to bistatic SAR imaging of moving ship targets,including echo modeling and characteristic analysis,as well as imaging of ship targets with diverse motion patterns.The main contributions of this work are as follows:1.This dissertation establishes echo models for moving ship targets with bistatic SAR under different sea conditions and analyze the echo patterns of bistatic SAR ship targets under two-dimensional translation and three-dimensional rotation conditions,laying the theoretical foundation for the research of imaging algorithms for ship targets under different motion states.2.To address issues like defocusing and offset in two-dimensional translation conditions of ships,this dissertation proposes a polar coordinate refocusing method for bistatic SAR ship targets.By constructing a bistatic elliptical polar coordinate imaging space,it eliminates the two-dimensional coupling of defocusing and offset,allowing for the estimation of ship target translational parameters and refocusing.3.Dealing with strong coupling of high-dimensional motion between the platform and the target under small amplitude rotation conditions of ships,this dissertation presents a ship target imaging method based on bistatic equivalent rotation velocity estimation.This method synthesizes high-dimensional coupled motion into onedimensional rotation,and then through the joint estimation of multiple scattering points and polar format focusing processing,the equivalent rotation velocity estimation and focusing imaging of the ship target are realized.4.Addressing challenges resulting from the large amplitude swing conditions of ships,which leads to strong Doppler spatial variation,this dissertation proposes a threedimensional reconstruction method for bistatic SAR ship targets.By estimating the Doppler parameters and establishing a bistatic range-doppler centroid-doppler frequency rate projection space,it separates spatially variable scattering points and achieves three-dimensional distortion-free reconstruction of ship targets in their local Cartesian coordinate system using joint estimation of ship three-dimensional rotation parameters.Through theoretical derivation,performance analysis,and experimental validation,this dissertation effectively verifies the aforementioned methods.The results demonstrate that these methods can effectively achieve imaging of bistatic SAR ship targets under different motion conditions.