Abstract

The spectral region from 8 to 14 μm is frequently used for thermal imaging and remote sensing of the earth’s surface. To interpret images and radio-metric data taken over snow-covered terrain, it is necessary to know the directional optical properties of the snow surface. Because ice is so highly absorbing in this spectral region, any reflection must take place at the first air-ice interface and therefore reflectance from snow should be modeled as reflection from a rough surface consisting of ice crystals. A simple model for bidirectional reflectance based on Fresnel reflectance coefficients and geometrical considerations has been described by Torrance and Sparrow.¹ This model has.only two free parameters, and they are related to surface condition. Preliminary measurements of the 8-14-μm bidirectional reflectance of snow are reported, along with calculations from the Torrance and Sparrow model. The measurements show that snow does behave as a rough surface and that artificially disturbing the snow surface does change its bidirectional reflectance. The model shows qualitative agreement and may be sufficient for describing snow, although better measurements are needed to determine its value.

© 1985 Optical Society of America