Research On The Rough Surface Grazing Angle Scattering Radiative Properties

All real surfaces,both those occurring naturally,and those fabricated artificially and with great care,are rough to some degree.It is therefore of interest,and often of importance,to study the rough surface scattering process.In this thesis,the geometric optics(GO)method and the Finite-difference Time-domain(FDTD)method are utilized to analyze the radiative properties of rough surface.The main contents of this paper are as follows.Firstly,the GO method is employed to calculate the bi-directional reflection distribution function(BRDF)of the rough surface.The GO algorithm starts by tracing the light bundles incident on the rough surface,and the Fresnel reflection is applied to each local point of intersection.Both the shadowing and the multiple scattering effects are considered during the ray tracing process.The “off-specular” reflection phenomenon is firstly analyzed based on the GO method.The results show that the “off-specular” reflection peak of the rough surface is due to the light enhancement of the rough surface under grazing-angle scattering and the edge shadowing effect.To explain the road surface mirage phenomena,a large scale rough surface scattering model is developed based on the GO algorithm.The rough surface is assumed to consist of small-scale rough surface facets.And the BRDF properties of the road surface are calculated.The results show that the average bidirectional reflectance distribution function value at the bright location is about twice that of the surface in front of the mirage.And the road surface mirage is due to a light-enhancing effect of the rough surface under grazing-angle scattering.To overcome the limited application region of the GO method,the FDTD method is employed to calculate the radiative properties of rough surface.To eliminate the staircase approximation error in the standard FDTD method and simulate the real shape of the rough surface,the boundary condition equations method is employed to modeling the rough surface interface.Then,the the improved FDTD method is applied to simulate the scattering properties of the cylinders and rough surfaces.The results show that the boundary condition equations method can effectively eliminate the staircase approximation error,and the FDTD algorithm can maintain the second order accuracy.The simulation results of the FDTD method,the GO method and analytical approximation models are compared,the results show that the FDTD method can overcome the limited application region of analytical approximation,and consider the interference effect that is lacked of in the GO method.To analyze and predict the occurrence of the specular reflection,diffuse reflection,the backscattering enhancement and the grazing-angle scattering peak phenomena,the FDTD method is employed to calculate the BRDF properties of rough surfaces with various roughnesses,correlation lengths and incident angles.