Volumetric optical properties of fully anisotropic participating media

The average absorption and scattering properties of participating media (PM ) are usually found from experiments, either a physical measurement or, if possible, a numerical ray-tracing experiment. The analysis of the experimen tal results is not simple when the medium is fully anisotropic i.e., extinc tion depends on the orientation of the incident radiation. Common approache s require a full solution of the radiative transfer equation (RTE) in the s ample, and an iterative optimization procedure to find the optical properti es. We present an approximate analysis method that is based on treating the sample as a single control volume. This leads to a direct, non-iterative s olution, using a set of algebraic equations rather than a full solution of the RTE. The procedure computes a representation of the optical properties for the most general case of anisotropy, which is compatible with the discr ete ordinate method or the finite volume method approaches. We discuss expe rimental error, the error due to the single control volume approximation, a nd the effect of the optical thickness of the sample. The performance and r obustness of the procedure are demonstrated for several test cases. (C) 200 1 Elsevier Science Ltd. All rights reserved.