The invariant imbedding approach is applied to the problem of diffuse reflection from a slab having a strongly elongated phase function. The diffuse radiation field is assumed to be axially symmetric. For both analytical and computational convenience, the study suggests using a simple rational function to approximate a strongly peaked phase function. Basic equations are derived for the reflection and source functions, and the reflection function is computed as the solution of an initial-value problem for ordinary differential equations. Numerical results are tabulated for increasingly fierce forward scattering. Two FORTRAN IV programs are included: one for the reflection function and the other for interpolation by expansion in orthogonal polynomials. 55 pp. Refs.
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