Research On Bistatic SAR Imaging Algorithm Based On Geosynchronous Orbit Irradiation Source

Bistatic SAR has flexible configuration by placing its transmitting and receiving subsystems on different platforms in space.It can not only improve the concealment and safety of the receiver,but also provide the condition of forward looking imaging by designing a reasonable configuration to make up for the defect that the monostatic SAR cannot carry out two-dimensional imaging of the target area.At the same time,geosynchronous orbit SAR has the advantages of short revisit time,large beam coverage area,strong anti-strike and anti-destruction capability,etc.Therefore,using geosynchronous orbit SAR as the irradiation source and carrying receivers on different platforms to form a bistatic SAR system,it can have the advantages of both geosynchronous orbit SAR and bistatic SAR.In this thesis,the imaging algorithms of geosynchronous orbit SAR as a source of radiation,a low-orbit satellite and a missile as a receiving platform are studied.The main research contents are as follows:1.Based on the space coordinate system and its conversion relations,in the case of considering the earth's rotation and satellite orbit,signal transmitting and receiving process of the high-low orbit bistatic SAR based on geosynchronant orbit sources and GEOMissile bistatic SAR based on geosynchronant orbit sources are analyzed respectively.Based on this,round-trip slant range history of each mode is deduced,and the echo model is established,which provide theoretical basis for the research of imaging algorithm.2.Three imaging algorithms are proposed for high-low orbit bistatic SAR based on geosynchronant orbit sources,which are improved NCS imaging algorithm,extend scene imaging algorithm and ?k imaging algorithm based on MSR spectrum.The improved NCS imaging algorithm directly fitted the range history of the scene center point to obtain the Taylor expansion coefficient of reference point,avoiding the error caused by the inaccurate equivalent velocity estimation of the transmitting and receiving satellite caused by the traditional NCS imaging algorithm.The extended imaging algorithm is used to fit the motion parameters with high order spatial variation,and the range and azimuth matching filters are designed to solve the two-dimensional spatial variation problem.The ?k imaging algorithm based on MSR spectrum represents the 2-D coupling term coefficients of each order as a linear combination of range-oriented and azimude-oriented position information,obtains a new stolt transform relation,and achieves the focused imaging of the target through 2-D non-uniform Fourier transform.The effectiveness of each algorithm is verified by point target imaging simulation,and the application scope of each algorithm is compared and analyzed.3.For GEOMissile bistatic SAR based on geosynchronant orbit sources,according to the geometric relationship between geosynchronous satellite,missils and target,the spatial variability of the echo is analyzed based on the history of the round-trip slant range history.For this problem,a generalized keystone transform imaging algorithm which can effectively correct linear and nonlinear range migration is studied,and the two-dimensional non-uniform Fourier transform is used to precise focus on the targets.The simulation results of flat trajectory and subduction trajectory show that the phase error introduced by the algorithm is small and the focusing effect of the point target is good.