Modeling the effect of sastrugi on snow reflectance

A snow reflectance model was developed to assess the bidirectional reflecta nce distribution function (BRDF) of snow over anisotropic rough surfaces su ch as fields of sastrugi commonly encountered in some areas of the ice shee ts of Antarctica and Greenland. The: sastrugi are modeled as regularly spac ed identical rectangular protrusions with the same orientation. Interfacet multiple scattering is ignored. Each model sastruga has vertical walls and a small width compared to its length and to its height. The input data for the model are the Sun and the viewing directions, the number of sastrugi pe r pixel, their dimensions and the bidirectional reflectance for a flat snow surface. The latter is computed by a multiple scattering model, and snow p articles are assumed to be spherical (Mie theory). In order to compare the model results with ground measurements acquired at the south pore by Grenfe ll et al. [1994] and Brandt et al. [1991], atmospheric effects were taken i nto account. The model reproduces the global influence of sastrugi on the s hape of the BRDF. The influence of sastrugi is clearly visible for zenith v iewing angles larger than 50 degrees.