MULTIPLE SCATTER OF COLLIMATED IRRADIANCE

The method of spherical harmonics is used to study multiple scattering of incoherent light (or other particles) in an optically thick medium with a plane surface. Techniques are reported that are particularly useful when scattered radiance has a forward peak that generates harmonics of very high degree. Convergence of computations hinges mainly on the small number of harmonics in the backscatter and not so much on the large number in the incident and forward-scattered light. The method uses annihilation operators to improve the solution by removing eigenfunctions that propagate the wrong way. Backscattered radiance at the surface may be calculated without solving for interior radiance.