Spaceborne Multi-baseline SAR Imaging And Moving Target Parameter Estimation

As an important means of earth observation,synthetic aperture radar(SAR),which has important significance in civil and military aspects,can achieve high resolution earth observation without the limitation of time,distance and weather.With the development of microwave technology and signal processing technology,the applications of SAR are not limited to 2D high resolution images of the ground,but also can realize the ground moving target detection and parameter estimation,three-and multi-dimensional imaging,holographic imaging and other tasks.The acquisition modes,which are used for distributed SAR,multi-static SAR and multi-pass SAR,are growing great interest in the current and future development of SAR imaging technology.Due to the spatial configuration of the baselines between each radar or trajectory in these SAR systems,they can be regarded as an extension of interferometry technology in time and space domains,and can be uniformly considered as multi-baseline SAR systems.However,different from the interference technology which is realized in image domain,multi-baseline SAR makes full use of the spatial configuration of baselines,realizes the ground moving /static targets observation in the space,time or frequency domain of echo signals,and of which the imaging algorithms are more complex.This paper focuses on the multi-baseline SAR data acquisition mode,fully analyzes the echo model,combines with the multi-dimensional signal processing technology,compressive sensing technology and polynomial phase signal processing technology,studies the 2D imaging,3D imaging,holographic imaging and moving target parameter estimation et al.,puts forward effective multi-baseline SAR imaging and moving target parameter estimation schemes,improve the multi-baseline SAR imaging and parameter estimation performance.The main research contents and contributions are as follows:(1)In this paper,a 3D space-time signal model for multi-baseline SAR echo is established under the condition of low orbit.And according to its Taylor equation,the influences of each phase of the target echo is analyzed.To solve the problems of the large amount of echo data in the multi-baseline SAR imaging and the difficult of hardware implementation in 2D sparse sampling,an ultra low PRF 2D imaging algorithm based on compressive sensing is proposed.Furthermore,refering to compressive sensing technology,a multi-baseline SAR 3D reconstruction algorithm based on convex optimization theory is proposed,which is applied for 3D reconstruction with sparse and non-uniform sampling in the height aperture.(2)The concept of spaceborne holographic SAR imaging is proposed.In order to realize the physical condition of multi-baseline circular orbit for SAR holographic,firstly,the formation mechanism of spaceborne circular trajectory is analyzed;the multi-baseline holographic imaging model is established under the condition of geosynchronous orbit;and the parameters of geosynchronous circular trajectory are designed.Then,a sub-aperture BP-compresseive sensing holographic imaging algorithm is proposed to complete the holographic reconstruction of ground fixed illumination scenes in time domain,with considerations of long synthetic aperture time,range-azimuth severe coupling,and non "stop-go-stop" data acquisition mode.(3)To breakthrough the limit that the current 2D velocity(range velocity and azimuth velocity)estimation of moving target parameters,an estimation method of 3D velocity(range velocity,azimuth velocity and height velocity)of moving target based on Fr FT is proposed.Firstly,a multi-baseline SAR echo model—two-order PPS(Polynomial Phase Signal)model of ground moving targets with 3D motion parameters is established;and the influences of the 3D velocity of the moving targets on the first-and second-order phase coefficients of the PPS are analyzed.Then,each order phase coefficients of multi-baseline SAR are estimated by Fr FT method;and the 3D velocity parameters of moving targets are optimized estimated by solving multi-baseline equations.The proposed scheme takes into account th e aerial sports,undulating ground,sea waves et al.influences on moving target velocity vector,realizes the estimation of range-,azimuth-and height-velocity.It can provide more reference information for 3D positioning and future motion trends about moving targets.(4)To expand the proposed 3D velocity estimation framework,and accurately describe the motion state of complex moving targets,a multi-dimensional motion parameter estimation method based on CPF(Cubic Phase Function)is proposed to estimate the velocity and acceleration in range,azimuth and height directions via multi-baseline SAR,which would more precisely describe the moving state of targets.Since the second-order PPS model cannot effectively estimate the multi-dimensional motion information,and considering the coupling characteristics among the six motion parameters,the moving target echo model is expanded into a higher order polynomial phase form,in which the correlation property among the six parameters are fully analyzed.At last,the 3D velocity and acceleration of moving targets are gradually optimized resolving.In this paper,the study on multi-baseline SAR imaging and moving target motion parameter estimation techniques are focused on the currentlly forward and technical problems in the earth observation field with distributed SAR,multi-static SAR,mutli-pass SAR systems.On the basis of analyzing the characteristics of multi-baseline configuration and echo model,rigorous theoretical deduction and scientific simulated and hardware-in-loop experiments are conducted to obtain 2D,3D,holographic images and moving target multi-dimensional motion parameters via multi-baseline SAR.The study will not only make full use of multi-baseline SAR configuration advantages,extend the multi-baseline SAR performance of stereo observation and moving target analysis,but also has some theoretical reference value for synthetic aperture sonar,ultrasonic array and other application fields with respect to the proposed multi-dimensional signal processing technology,compressive sensing technology,polynomial phase signal processing technology.