Research On Ray Tracing Algorithm For Analysis Of EM Scattering From Layered Rough Surface

Research on EM scattering from random rough surface has significant academic value and broad application prospect in microwave remote sensing, target detecting and recognizing. As the practical surfaces are often double layered or multilayered, research on the electromagnetic scattering from layered rough surface is of great importance. Ray tracing algorithm is applied to study the EM scattering from 1-D and 2-D layered rough surface under Kirchhoff approximation, such as soil surface covered by snow and sea surface covered by oil.This paper introduces the Monte Carlo method for random rough surface modeling, and the 1-D and 2-D rough surfaces with different statistical parameters are simulated. Combining the Helmholtz equation and the boundary conditions, the mean reflected and transmitted intensities are obtained. By introducing Kirchhoff approximation, the integral expressions of the transmitted and scattered field under different polarizations are derived. The generated rough surface is discrete into a series of line segments. The scattered and transmitted field of each segment is obtained under the condition of far field approximation, so as the reflection coefficient and transmission coefficient. With the law of conservation of energy, the correctness of this method is verified. The influence of root mean square, correlation length and dielectric constant on the EM scattering from one-dimensional rough surface is studied.The ray tracing algorithm is applied in solving the coordinates of incidence, reflection and transmission point, thus the phase differences between them can be calculated. The EM scattering from 1-D rough surface varies along with the height of RMS, the thickness of the middle-layered medium, the dielectric constant of middle layered medium and the underlying medium are given. The equivalent dielectric constant of the snow and soil with different frequency and temperature are discussed. Numerical calculation and analysis of EM scattering of the soil with snow covered varies with the RMS height and correlation length, soil moisture and etc. The sea surface with oil film covered is simulated with modified PM spectrum, thus the EM scattering is discussed taking the oil film thickness and wind speed into consideration. The scattering of PM spectrum and modified PM spectrum under different polarization are compared, proving the effectiveness of the modified sea spectrum.This paper calculates the EM scattering from 2-D rough surface under the Kirchhoff approximation with tapered wave incidence. Numerical calculation and analysis of the variation of rough surface scattering coefficient with different parameters of the rough surface is given. The ray tracing method is applied to 2-D layered rough surface, giving the methods of determining the direction of reflection ray and transmission ray, so as the method of intersection test. Based on the geometry characteristics of hierarchical rough surface, the accelerating method of coarse-fine grid method and he feasible region searching method are put forward. Numerical calculation and analysis of the variation of the scattering from 2-D layered rough surface with the dielectric constant, dielectric layer thickness, RMS height and relative length and etc.