title: Comparisons of bidirectional reflectance distribution function measurements on prepared particulate surfaces and radiative-transfer models.
abstract: To understand the connection between single-particle optics and the optics of a closely packed surface, controlled laboratory measurements of bidirectional reflectance distribution functions on layers of polymer and glass spheres are carried out. The measurements are compared with predictions from five radiative-transfer models; the Hapke's models, the Lumme-Bowell model, the BRF algorithm of Mishchenko et al., and the discrete ordinate radiative transfer. It is found that models of strict numerical radiative-transfer equations (RTEs) predict measurements well in some regions but have errors in both forward- and backward-scattering directions. The improved Hapke's model, although it has an anisotropic multiple-scattering term, still produces considerable errors compared with the strict RTE. The difference can be attributed to the exclusion of a diffraction contribution in the Hapke model.
authors.affiliation: Department of Physics, University of Miami, Coral Gables, Florida 33124-8046, USA.
authors.forename: Hao
authors.initials: H
authors.lastname: Zhang
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Voss