Research On Electromagnetic Scattering Modeling And Imaging Of Typical Landforms

This article mainly studies and analyzes the scattering characteristics of typical landforms such as vegetation,soil,and concrete,and studies and analyzes the calculated scattering fields or scattering coefficients.We generally use the analytically approximated surface scattering method to perform scattering calculations on rough surfaces.This method is more accurate for terrains such as bare soil and sandy land where the volume scattering can be ignored.However for multi-layer scattering models such as the two-layer vegetation scattering model,the scattering results calculated by ignoring the volume scattering components will have a larger error than the actual results.Therefore,this paper will also focus on the scattering characteristics of the two-layer vegetation scattering model.The dielectric constant is a very important parameter when calculating the scattering field of the rough surface.It has a great influence on the scattering characteristics of the rough surface.Therefore,we need to be able to accurately give the value of its dielectric constant under different scattering conditions.The more effective method is to establish equivalent permittivity models for different types of landforms,so that we can use the empirical model formula to solve the permittivity in different environments.In this paper,the equivalent permittivity models of soil,vegetation,sand,and concrete are studied and analyzed.After the dielectric constant is given,for different sizes of rough surfaces,we need to use different surface scattering calculation methods to study and analyze the scattering characteristics.The surface scattering calculation methods introduced in this article are mainly Kirchhoff's approximation(KA),perturbation(SPM),small slope approximation(SSA),integral equation method(IEM),and improved integral equation method(AIEM)and so on.In chapter two,the applicable conditions of different analytical approximation methods are discussed and analyzed.For a two-layer rough surface,such as a two-layer vegetation scattering model,if only the surface scattering coefficient is calculated,the theoretical result obtained will be smaller than the actual value.This is mainly because the volume scattering field of the scattering element in the vegetation layer is ignored.Therefore,the calculation of the two-layer rough surface requires the calculation method including volume scattering.In this paper,the vector transmission theory method of the non-coherent scattering model and the Monte-Carlo simulation method of the coherent scattering model are mainly used.The vector transmission theory method is mainly to calculate the scattering coefficient of the vegetation model by studying the scattering energy of the vegetation model,and the Monte Carlo simulation method is to first record the position information of the scattering elements in the vegetation layer and then calculate it.Through these two methods,the single-site scattering and doublesite scattering of the vegetation model are calculated,and the relationship between the scattering coefficients under different frequency bands and different incident angles is analyzed.Compared to the vector transmission theory method,the total scattering field calculated by the Monte Carlo simulation method includes a coherent scattering field,so its accuracy is higher in the specular scattering direction.Therefore,although the computational time complexity of the Monte Carlo simulation method is much larger than the vector transmission theory method,with the improvement of computer performance and the emergence of parallel computing,the problem of computing efficiency will be solved.For the primary vegetation and cluster distribution vegetation,the scattering results calculated by different cluster distribution types are different.Therefore,the scattering characteristics of the cluster regular distribution vegetation model and the cluster random distribution vegetation model are studied and analyzed.Finally,the backscattering characteristics of the three-layer vegetation model were studied.In the last chapter of this paper,imaging research and analysis are performed on the scattering coefficients and scattering fields calculated from typical surface calculations.There are two main methods of imaging the surface: SAR imaging and ISAR imaging.SAR imaging is mainly used in scenarios where the target is stationary and the radar is moving.ISAR imaging is mainly used in situations where the radar is stationary and the target is moving.In Chapter 5,the imaging analysis mainly focuses on the exponential spectrum rough surface and power spectrum rough surface.The imaging of typical landforms is a very important research work in microwave remote sensing.Through the calculation of scattering on different surfaces and the research of radar imaging,imaging results of different terrains can be obtained.In order to better study the scattering characteristics of typical landforms,this paper will interpolate the elevation information model(DEM)in the geographic information system(GIS)and calculate its scattering coefficient.Because there are many types of terrain in the elevation information model,terrain classification and empirical models are needed to calculate its scattering field.This paper will use the modified Morchin model to study and analyze its backscattering characteristics.