Electromagnetic Scattering Model Of Layered Ground

Microwave remote sensing has become an important tool for the Earth's observa-tion.With satellites launched by all world countries and the acquisition of radar data,it is necessary to conduct research on the microwave scattering characteristics from ground objects.To enrich the quantitative interpretation on the Earth's geometric infor-mation and dielectric property using microwave remote sensing techiniques,one needs to fully understand the interaction between electromagnetic wave and Earth's objectives.Therefore,the study on the electromagnetic(EM)propagation of layered ground is of great importance.This dissertation presents a complex layered ground scattering model including two intermediate variables,i.e.,an effective dielectric constant(EDC)model of the complex layered ground and the roughness of land suface.The model is categorized into the three parts:(1)extract the geometric information and dielectric property of the com-plex layered ground,and conduct two experiments for realistic ground parameters and the scattering fields of ground;(2)study the interaction between EM wave and the complex layered ground;(3)develop an effective dielectric constant(EDC)model of the complex layered ground.The invovations and researchs of this dissertation are given as follows:In order to improve the calculation efficiency of surface electromagnetic scattering,this dissertation proposes the Decomposition and Reconstruction Theorem(DRT).The theorem first decomposes a surface profile into a series of basic profiles described by triangular basis functions,then linearly combines the basic contours to obtain a set of test profiles based on the surface roughness,and reconstructs the scattering of original surface by using the scattering of the test profiles.Since each test profile contains only a few basic profiles,the scattering field of the test profile can be solved easily by current EM scattering models of random rough surface.The DRT enables parallel computing technology to be applied to the EM scattering of random rough surfaces,and solves the problem of low calculation efficiency in the scattering evaluation of complex random rough surfaces.The DRT also explains the physical mechanism between EM waves and the surface profile,laying the foundation for the accurate inversion of the surface profile from the radar echo signal.To solve the scattering of the random rough surface,this dissertation proposes two new models,i.e.,both the Trauncated Extended Boundary Condition Method(TEBCM)and the Finite Difference and Time Domain(FDTD)method are combined with the DRT,which are referred to as TEBCM-DRT method and FDTD-DRT method.When the calculation difference is less than 3 d B,the performanced efficiency of the TEBCM-DRT method is increased by 2.0×10~5 and 7.4×10~2 times,respectively,com-pared to the TEBCM method without DRT and the traditional method of moments(Mo M);the calculation efficiency of the FDTD-DRT method is increased by 8.0×10~2times compared with the traditional FDTD.Subsurface profile is one of the key parameters for constructing an accurate scat-tering model of multilayer structure.Due to the difficulties of tracking the subsurface profile,subsurfaces are usually approximated to be flat.The lack of the applicable con-ditions for subsurface approximation affects scattering models of multilayer structure being used in inversion algorithms.To solve this problem,the difference between the scattered fields of two structures are analyzed:a two-layered dielectric structure with a rough subsurface and a two-layered dielectric structure with a flat subsurface.The scat-tered fields of the two structures are solved by the scattering model that combines Method of Moment combined with the Kirchhoff approximation method(KA).The re-sults indicate that the difference are determined by the surface roughness,medium thickness,and incidence angle.By assigning these parameters with different values,this dissertation quantitatively evaluates their impacts on the difference in bistatic and backscattering scattering coefficients between the structures.Finally,the applicable conditions of the flat subsurface approximation are determined by limiting the differ-ence less than 1 d B,improving the accuracy of it used in inversion algorithms.This dissertation proposes an Effective Dielectric Constant(EDC)model to de-scribe the influence of multiple rough surfaces on electromagnetic scattering.By finding the equivalent structural EDC model of the reflection coefficient between the multilayer ground structure and a single homogeneous medium,the interaction mechanism be-tween the electromagnetic wave and the complex multilayer ground surface along the mirror direction is explained,and the macroscopic dielectric properties of the multilayer structure are characterized.Subsequently,the scalar Kirchhoff approximation(SKA)method based on the EDC model(SKA-EDC)is proposed,which simplifies the calcu-lation of complex multi-layer surface scattering to the scattering problem of a single uniform medium.With above models,a process model for the scattering of the complex layered ground is built.The results are:EM scattering coefficients--the EDC model and surface roughness,and the EDC model--ground parameters,providing an easily imple-mentable forward scattering model for surface quantitative inversion algorithms.Based on the SKA-EDC method,this dissertation studies the sensitivity of the EDC on different soil moisture,soil thickness and surface roughness,and compares the difference between the bistatic coherent scattering coefficients at the P-band and the L-band.The results show that the EDC model can characterize the influence of the die-lectric properties and geometric properties of the multilayer structure on the bistatic scattering coefficient,and can provide additional information for the soil moisture in-version in the rooted area.This study also proved that for a wide range of actual surface environments,the P-band radar echo signal is more sensitive to changes on soil mois-ture in the rooting area compared to the L-band radar echo signal.This study can pro-vide theoretical support for the design and development of the next generation micro-wave remote sensing satellites.