Ray tracing models are known to yield accurate results if a sufficient number of terms (e.g. diffraction mechanisms) are accounted for in the asymptotic formulation. For wireless applications one desires a ray analysis in which the fewest number of terms are retained, to obtain accurate and computationally efficient results. When retaining a subset of scattering mechanisms in a ray solution, validation is desirable via a rigorous numerical model. In the work presented here the multilevel fast-multipole algorithm is used to validate ray-tracing models for complex environments, including forest-like media. © 2004 IEEE.