Imaging And Positioning Method Study On Curved Trajectory Bistatic Forward-Looking SAR

Owing to the characteristics of multi view observation and passive reception,bistatic forward-looking SAR is widely used in military and civil fields.Due to the characteristics of its own 3D acceleration,the maneuvering platform can realize the special application requirements in complex environment independently and flexibly.The application of bistatic forward-looking SAR technology on maneuvering platform can realize curve trajectory bistatic forward-looking SAR(CTBF-SAR)imaging.CTBF-SAR is a new bistatic Imaging mode,which combines the 2D forward-looking imaging ability of bistatic forward-looking SAR with the trajectory planning ability of the maneuvering platform,breaks the inherent limitations of monostatic SAR,and can provide the whole process 2D forward-looking highresolution imaging capability for aircraft blind landing and missile guidance.However,in this mode,the signal has the characteristics of range migration spatial-variant,Doppler parameter coupling spatial-variant and large accumulation of INS error,which increase the difficulty of imaging and positioning.In this thesis,the key problems on CTBF-SAR imaging and positioning methods are discussed.The main contents of the thesis are as follows:1.The geometric configuration and system parameters of CTBF-SAR are the preconditions of the imaging methods,as the result of the mapping relationship between them and imaging resolution is complex,which is difficult to be determined as simple as SAR.Firstly,the imaging geometry suitable for curve trajectory motion is established,and the system parameter selection and optimization design method are given,which improves the parameter design accuracy and saves the system resources;Secondly,based on the gradient principle,the expression of multi parameter coupling resolution is derived to clarify the characteristic parameters affecting the imaging ability.Then the configuration parameters and system parameters are inversely constrained,which can reduce the difficulty of parameters design.2.In the case of wide-swath and long synthetic aperture time accumulation,the maneuvering platform CTBF-SAR has the problems of strong coupling and strong 2D spatial-variant of echo Doppler parameters.To solve this problem,an azimuth extended NCS imaging method based on spatial-variant order is proposed.This method constructs a high-precision slantdistance model based on Chebyshev orthogonal polynomials,which has the best uniform approximation characteristic of slant-distance;On this basis,the echo signal is decoupled in2 D,the spatial-variant of doppler parameters with slant-distance and azimuth focusing frequency is quantitatively analyzed.Taking π/4 phase threshold as the standard,the 2D spatial-variant correction function suitable for the spatial-variant order is designed by using the least square fitting algorithm,and the azimuth extended NCS imaging method is proposed,which eliminates the 2D spatial-variant and improves the imaging focusing accuracy;Finally,based on the principle of back projection,taking full advantage of the slant-distance and doppler information of the proposed imaging method,a geometric deformation correction method is proposed.The results of point target simulation and real data processing verify the good focusing performance and geometric deformation correction ability of the proposed method.3.In the autonomous homing stage of maneuvering platform,to solve the problem that the traditional positioning methods are limited by the accuracy of parameters such as speed and angle,an analytical-iterative positioning method is proposed.Firstly,based on the position information of image matching points,the slant-distance positioning model of maneuvering platform CTBF-SAR is established,and the analytical solution set of the positioning model is analyzed and deduced.Then,according to the characteristics of INS data,the unique analytical solution is determined.But the solution is colse to the real position.Therefore,taking the solution as the initial iteration point,the Jacobian matrix is established,and the optimal 3D coordinates of the receiving radar is quickly obtained through Newton iterative search to complete the accurate positioning of the maneuvering platform.On this basis,the motion error and matching error models are established,and their influence on the positioning accuracy is analyzed through simulation experiments.The results show that the proposed method has high positioning accuracy and speed.