Improved steady-state diffusion approximation with an anisotropic point source and the [delta]--Eddington phase function

Using the algebra transformation method, we develop and demonstrate the use of the [delta]-[P.sub.1] approximation to improve steady-state radiative-transfer estimates on spatial scales comparable to the mean free path. We show that the [delta]-[P.sub.1] approximation agrees well with Monte Carlo simulation from source to infinity when we choose an appropriate parameter f(fractional portion that scatters directly forward) in the [delta]-Eddington phase function. We also provide the empirical formula to determine the parameter f. OCIS codes: 030.0030, 290.0290, 290.7050.