All the surfaces show some roughness at different length scale. This affects the spectral radiative properties of the material. Statistical measures are used to quantitatively describe about the randomly rough surfaces.Scattering of electromagnetic waves from such surfaces are studied using computational methods.Bireflection Distribution Function (BRDF) is computed using Finite Difference Time Domain (FDTD) method andGeometric Optics (GO) ray tracing method.In FDTD, Maxwell’s equations corresponding to the scattering of electromagnetic waves from the rough surface are solved numerically. Electric field and Magnetic field are set up on mesh grid at discrete steps and the fields are updated in discrete time steps.One needs to choose parameters such as mesh size, time steps, surface size etc. appropriately. This method produces accurate radiative properties but it is computationally intensive. In GO, surface is approximated as locally smooth and scattering event from such surface is treated as a specular reflection. In this way, it produces reasonably accurate radiative property predictions in some cases even if interference and polarization effects are not considered. Radiative properties of rough surfaces will be discussed after computing their BRDFs using both FDTD and GO. Since both the methods (FDTD and GO) have some limitations in terms of computational requirements and accuracy,therefore it is important to quantify the accuracy of GO approximation so that one could solve the problem with little computational effort.
 K. Fu, P.F. Hsu, New regime map of the geometric optics approximation for scattering from random rough surfaces, J. Quant. Spectrosc. Radiat. Transf. 109 (2008) 180–188.
 A. Bergström, D. Powell, J. Kaplan, A ray-tracing analysis of the absorption of light by smooth and rough metal surfaces, J. Appl. Phys. 101 (2007) (113504/1- 11).