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Results of measurements of the bidirectional refleclion function of snow for the solar zenith angle close to 54° are compared with a recently developed snow optical model based on the representation of snow grains as fractal particles. The model has a high accuracy out of the principal plane for the observation zenith angles smaller than 60°. However, the accuracy is reduced in the principal plane. Specular light reflection by partially oriented snow plates on the snow surface not accounted for by the model can play a role for measurements in the principal plane. The model discussed can be used for the grain size retrieval using both ground and spaceborne measurements of the snow reflectance. This is sup- ported by a high accuracy of the model in a broad spectral range 545-2120 nm as demonstrated in this work. [ABSTRACT FROM AUTHOR]

Snow accumulation rate is an important parameter in determining the mass balance of polar ice sheets. Accumulation rate is currently determined by analyzing ice cores and snow pits. Inadequate sampling of the spatial variations in the ice sheet accumulation has resulted in accumulation rate uncertainties as large as 24%. We designed and developed a 600-900-MHz airborne radar system for high-resolution mapping of the near-surface internal layers for estimating the accumulation rate of polar ice sheets. Our radar system can provide improved spatial and temporal coverage by mapping a continuous profile of the isochronous layers in the ice sheet. During the 2002 field season in Greenland, we successfully mapped the near-surface layers to a depth of 200 m in the dry-snow zone, 120 m in the percolation zone, and 20 m in the melt zone. We determined the water equivalent accumulation rate at the NASA-U_1 site to be 34.9 ± 5.1 cm/year from 1964 to 1992. This is in close agreement with the ice-core derived accumulation rate of 34.6 cm/year for the same period. [ABSTRACT FROM AUTHOR]