Research On ISAR Imaging Of Ship Based On Range-instantaneous Doppler Algorithm

Because of the complexity of ship target motion,the high-resolution ISAR imaging technology of ship targets at sea has been a hot research topic both at home and abroad.The echo signal of ship targets is non-stationary,and the Doppler frequency is time-varying.At this time,the traditional Range-Doppler imaging algorithm can not get clear ISAR images,and the Range-Instantaneous Doppler algorithm is needed for imaging.In this paper,based on the motion characteristics of ship targets,the Doppler frequency of the scattering point echoes of ships are approximately described by non-stationary signal models.The emphasis is on how to achieve high-resolution ISAR imaging of ship targets in different sea conditions.The main work is as follows:The principle of ISAR imaging and motion compensation technology are introduced,and the influence of translation component on image blurring is analyzed.The effective envelope alignment and phase compensation methods are selected to further process ISAR imaging.The simulation results show that motion compensation technology can effectively suppress image defocusing caused by target motion and improve image quality.The motion characteristics of the ship’s target are analyzed,that is,the motion of the ship’s target scattering point can be regarded as its three-dimensional rotation around the ship’s centroid and the synthesis of the ship’s navigational motion with respect to the radar,and the ship’s movement is established.The echo model,through which the simulated echo data of the ship target is obtained.The imaging principle of RID algorithm is introduced.For the simulated echo data,RD algorithm and RID algorithm are used for imaging.The imaging results show that the RID algorithm has better imaging effect and can obtain the attitude of the target at different moments.Under certain conditions,the three-dimensional rotation is the main source of ship target imaging.In order to solve the ship ISAR imaging problem under low sea conditions,the ship echo is constructed into a multi-component LFM signal model.The RID algorithm based on bilinear time-frequency distribution is used to image the ship target,and various bilinears are studied.Time-frequency distribution and its application in ISAR ship imaging.Then through the simulation imaging results to compare several time-frequency distribution methods,it is concluded that the rearranged Cohen method has better time-frequency aggregation and can effectively suppress the cross-term interference.It is the best for the ship ISAR transient imaging in low sea conditions.Aiming at the problem of ship ISAR imaging under high sea condition,the ship echo is constructed into a multi-component CPS model,and the parameters that are modeled as CPS signals in each distance unit are estimated by RID parameterization technique to generate a well-focused instant.ISAR image.Firstly,the PHMT parameter estimation method is introduced,and then the PHMT algorithm is improved to some extent according to its shortcomings.It is used to suppress the autocorrelation term of the cross term and the amplified signal,thus improving the accuracy of parameter estimation.Later,a parameter estimation method with higher real-time performance is introduced.The simulation results demonstrate the effectiveness of the RID imaging algorithm based on CPS model parameter estimation method under high sea conditions.It also shows that the improved PHMT algorithm improves the image contrast of ISAR imaging and proves the effectiveness of the improvement.