Research On Automatic And Forward Methods To Establish Monostatic And Bistatic Scattering Center Models For Complex Targets

In recent years,the method to acquire the scattering characteristics of radar targets in monostatic or bistatic mode is increasing explosively with the development of high-resolution radar technology.However,the target information interpretation technology is relatively backward,and the huge information data has not been fully transformed into the achievements for target recognition and intelligence acquisition.As the essential feature of radar target electromagnetic scattering at high frequency,the scattering center model enables a concise description of radar targets,and reflects the electromagnetic scattering characteristics of the targets.Besides,due to its reduced storage requirement and flexible extended operation conditions,etc,it is useful for fast prediction and interpretation of scattering characteristics.Therefore,the study on scattering center has attracted great attention.The method to establish scattering center model include two aspects,the one is inverse method;And the another is the forward method,which obtains scattering centers and determinates model parameters directly from a computer-aided design(CAD)model of the target through theoretical analysis of electromagnetic scattering mechanism.The forward method avoids complex iterative optimization process,which not only greatly reduces the amount of computation,but also provides clear correspondence of the scattering centers.Therefore,the forward method helps to understand the scattering mechanism of radar target,and opens up a new auxiliary means to establish target characteristics database for model-based synthetic aperture radar(SAR)automatic target recognition(ATR).However,the current forward method is not automatic enough,which requires professionals to participate during modeling.For example,it is necessary to judge whether the scattering centers are distributed by simulated or measurd SAR images,and manually read the length parameter.In order to determine the frequency dependence parameter,the scattering mechanism of the scattering source is also distinguished by professionals according to the target's CAD model.Manual intervention not only reduces the efficiency of modeling,but also makes mistakes easily.Except that it is not automatic enough,bistatic radar can observe the target from multiple perspectives,so it can capture the specular reflection which does not exist in the monostatic mode,and obtain more abundant scattering information,but there is no research on forward modeling method of scattering center in bistatic mode.Considering the above problems,this paper firstly studied the automatic and forward modeling method of scattering center and its application in monostatic mode.Following this,the bistatic scattering characteristics are analyzed and studied.On this basis,the forward modeling method of bistatic scattering centers is also proposed for complex target.The main content of this paper are as follows:1.Study on Automatic and Forward Method to Establish Parametric Scattering Center Models of Complex Targets for Monostatic Radar(1)An automatic and forward method is realized to establish parametric scattering center model of complex targets.In addition,the modeling code,which is called the FMPM,is also developed.Only the CAD model of the complex target needs to be input,the scattering centers can be output,as well as their physically relevant parameters.Since the modeling method is fully automatic,it can effectively establish the scattering center model for complex targets(2)A set of automatic approaches is developed to determine the more general length parameter and the frequency dependence parameter of scattering center.The scattering mechanism of distributed scattering center is expanded from typical scattering structures and specular reflection mechanism to a more general case,thus establishing the distributed scattering center models formed by curved surfaces with large curvature radii.The frequency dependence parameter is determined by the principal curvature radii of the component surface,which are calculated with differential geometry theory,thus avoiding the complicated artificially prejudgment of the scattering mechanism.(3)Based on the automatic modeling method,the parametric scattering center models of several targets in MSTAR are established.The reconstructed characteristics are consequently compared with the reference data provided by MSTAR or other reliable database.To quantitatively illustrate the validity of this method,the normalized similarity of the SAR images and the matching rate of the position parameters are used to evaluate the similarity,and the results of this method are verified.(4)A preliminary technology is expanded to diagnose and correct scattering center models of non-cooperative targets whose CAD models are unknown or partially known.Since the modeling method in this paper is automatic and efficient,and the correspondence between the scattering center and the scattering structure is much clearer,it can be applied to improve the accuracy of the scattering center models for the non-cooperative target.It can be expected that this technology will play an important role in target recognition.2.Study on Forward Method to Establish Parametric Scattering Center Models of Complex Targets for Bistatic Radar(1)A prediction method of the high-frequency scattering characteristics for bistatic complex targets are realized.The PO method is used to calculate the single scattering of the target,and the hybrid GO-PO method is used for the coupling scattering.This prediction method can simulate RCS characteristics and SAR images of complex targets.In addition,this paper also studies the bistatic SAR imaging method by using PFA algorithm,and focusing on the analysis of the bistatic resolution characteristics,and the line of sight polar interpolation(LOSPI)method.Finally,the bistatic RCS pattern and SAR images of several targets are simulated,which can provide theoretical basis and technical support for the bistatic scattering centers modeling.And compared with the simulation results of FEKO,the method is verified by the accuracy.(2)A forward modeling method is proposed to establish scattering center of the complex target in bistatic mode.Refer to the monostatic automatic modeling method,the scattering centers are separated directly from the CAD model of the target by using the ray tracing and clustering with physical optics(PO)technology in bistatic mode.And the physically relevant parameters are also determined by analyzing scattering mechanism,focusing on the determination of 3-D position parameters.In addition,this paper also summarizes the expression of the bistatic attributed scattering center model based on 3-D response models of six typical shapes.Finally,numerous bistatic scattering center models of the typical shapes and complex targets are established,and the reconstructed RCS and SAR image are compared with the simulation results.The results verify the effectiveness and accuracy of the method.