Study on scattering of Gaussian beam by two dimensional dielectric rough surfaces

The modification of the Kirchoff approximation theory for rough surface scattering by an incident Gaussian beam instead of a plane wave is developed based on conventional Kirchoff scattering theory and a plane wave spectrum expansion method. A close form for the normalized coherent scattering cross section is derived when the linear dimension of a rough surface patch is twice as large as the beam size. It is shown that provided the incident Gaussian beam size is much larger compared with the surface height correlation length, the normalized scattering cross section is the same as for an incident plane wave.