| Moving target detection and imaging based on the radar system can be divided into single-channel methods and multi-channel methods.The single-channel system cannot solve the problem of slow moving target detection under strong clutter since the limitation of its structure.Therefore,this thesis studies the moving target detection,positioning and velocity measurement in the dual/multi-channel interferometry systems,and applies this theory to ship target imaging.Based on the accurate positioning of moving target by dual/multi-channel systems,the motion compensation method of ship target is studied for the realization of ship target imaging.In addition,considering the particularity of the actual background of ship target imaging,the simulation and suppression methods of sea clutter in dual/multi-channel systems are studied to improve the detection performance of ship targets.The main contents of this thesis are as follows:In the first chapter,synthetic aperture radar(SAR)and its development are briefly introduced.The research significance and history of moving target detection and imaging are described in detail.The characteristics of ship movement and imaging are analyzed as well.In the second chapter,the linear range-doppler algorithm is introduced firstly.Then the expressions of ideal airspace cancellation weights are derived in three kinds of dual/multi-channel systems,i.e.,the dual-channel,the sum/difference beams and the three-channel systems.The azimuth angle,abscissa and radial velocity of the moving target can also be estimated.The results of moving target detection based on dual/multi-channel interferotry,as well as the quantitative analysis of moving target location,velocity measurement under different signal to clutter ratios,are completed through simulations.The performance of different systems is also compared.In the third chapter,the simulation and suppression methods of sea clutter for dual/multi-channel systems are studied considering the presence of sea clutter in practical ship imaging.Firstly,an amplitude distribution model of K-distribution sea clutter is discussed.Then two feasible sea clutter suppression methods,the adaptive clutter suppression interferometry and a reduced-dimension space-time adaptive processing method(3DT-STAP),are studied under this model.The simulation results show that 3DT-STAP can effectively suppress sea clutter,which can meet the requirement of ship target detection in sea clutter.In the fourth chapter,based on the theory of moving target localization and velocity measurement in dual/multi-channel systems,an algorithm for ship target imaging combining digital focusing process and generalized second-order Keystone transform is proposed.With reference to a certain type destroyer,the simulation model of the ship appearance and three-dimensional motion are both built.The results of ship positioning,velocity measurement and imaging in the three-channel system are given respectively under 0 and 5 level sea conditions,which prove that the proposed method can obtain well focused SAR images of moving ship targets.The fifth chapter is the concluding remark,which summarizes the content of the full text,and points out the problems that need to be further studied. |
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