Research On Inverse Synthetic Aperture Radar Imaging Of Multi-targets

Imaging Radar has been widely used in military and civil fields as an al l-day and all-weather active remote observation method.As an important part of the imaging Radar,the Inverse Synthetic Aperture Radar(ISAR)has been studied extensively.At present,the ISAR imaging technology of stable moving target has been basically ripe.Therefore,the researchers focused on ISAR imaging in complex situations,and the multi-targets belongs to the complex situations.In this paper,the multi-targets ISAR imaging is divided into two categories according to the difference of motion state of the targets: multi-targets with large difference in motion state and multi-targets with similar motion state.According to the characteristics of two imaging scenes,the corresponding image processing algorithm is proposed.The main work of the article is as follows:(1).Firstly,this paper introduces the basic principle of ISAR imaging and analyzes its signal processing process of high resolution of range direction and azimuth direction.Then the stationary uniform rotation model and the Range-Doppler(RD)imaging algorithm are introduced.Expounde the function and necessity of motion compensation for ISAR imaging,and analyze several common motion compensation methods by measured data.This paper quote the Range-Instantaneous-Doppler(RID)method to solve the difficulty of non-stationary moving targets imaging.Finally,A RID imaging method based on the multiple component third-order phase signal model is introduced.The above basis lay a theoretical foundation for solving the problem of multi-targets ISAR imaging.(2).Establishe the 3-D spatial motion model and the Radar echo signal model of multi-targets ISAR imaging.By analyzing the characteristics of echo signal,it is clear that the difficulty of multi-targets ISAR imaging lies in motion compensation.In order to solve this problem,this paper considers the motion compensation based on motion parameters search and minimum entropy of image.The entropy of the ISAR image will be minimum when the motion compensation is processed by the motion parameters of target.In order to avoid using the traversal algorithm with the large computation.This paper borrows the existing particle swarm optimization(PSO)algorithm to realize the fast and accurate motion parameter estimation.Clear imaging results of each target can be obtained through target elimination in the image domain and multiple iterations.Finally,the imaging results of simulation data demonstrate the effectiveness of the multi-targets imaging method based on motion parameter search.The limitations and possible improvements of the method are discussed by analyzing the imaging process.(3).Aiming at the limitation of the PSO algorithm and the motion state of the real ship target,a multi-target ISAR imaging method based on image processing is proposed.This method can be used to separate the targets in the image domain and refocus the image separately when the target is in a similar motion state.Because of the ships in fleet sailing are usually close to,the range profiles of the targets usually superposite.In addition,due to the speed difference between the targets,the location of the targets in Doppler direction is relatively random.Therefore,it is not reasonable to simply segment the target s from azimuth direction or range direction.This paper want to use the geometric clustering method to achieve the effective segmentation of targets with random distribution.However,due to the sparsity and random noise distribution of ISAR images,geometric clustering method cannot be applied to ISAR images directly.Therefore,this paper innovatively uses a series of image processing methods to transform sparse ISAR image with strong noise into multiple independent target areas with clear edge and internal connection.After the targets are segmented and extracted by geometric clustering method in the complex image domain,the data of the target is reversely transformed to the echo domain and the image processing of each target is carried out respectively.The method has been validated by simulation and measured data,and the imaging effect is good.