Multiple scattering by randomly distributed obstacles--Methods of solution

Methods of solution of problems of multiple scattering of electromagnetic radiation by randomly distributed obstacles are evaluated with respect to generality, accuracy, and suitability for numerical calculations. Exact solutions are found to be limited to infinite regions and are difficult to apply for anisotropic scattering. Approximate solutions of the transport equation are limited to simple regions and are very complicated for anisotropic scattering. Approximate representation of the scattering process with the classical diffusion equation permits solution for almost all conditions, but the solution is inaccurate near the boundaries of the region of scattering. Approximate representation of the intensity by a number of discrete components permits solution for many geometries. Several two-component representations have been developed which yield more accurate results than diffusion theory for anisotropic scattering. A six-component model appears to be considerably more accurate for most geometries but requires machine computations.