This paper was presented at the Art, Science and Applications of Reflectance Spectroscopy Symposium sponsored by ASD Inc. and IEEE GRSS, February 23-25, 2010 in Boulder, Colorado.

Author: Thomas Howell Painter
Affiliation: Snow Optics Laboratory, University of Utah, Salt Lake City, UT  USA

Abstract

Snow cover represents a critical component in Earth’s regional and global climate and hydrologic cycle. While the snow-albedo feedback is perhaps the most sensitive in controlling the Earth system response to changing climate, the albedo of snow across the globe is poorly understood and characterized. Recent advances in instrumentation, modeling, and scientific inquiry substantially improved our understanding of the spatial and temporal forcing of and by snow cover. In particular, field and imaging spectroscopy have facilitated inference of the influences on broadband and hyperspectral directional reflectance by snow grain size, grain morphology, snow impurities, surface liquid water content, and biological content. Despite these advances, the literature is still populated with erroneous inferences of snow properties from remote and field directional reflectance signatures. These errors result largely from the complexity of the snow system with its inclusions beyond the simple matrix of ice. In this review, I address the variation in measurements of snow spectral albedo and directional reflectance with respect to the basic scattering physics of ice, and the inclusions liquid water, dust, soot, and algae, as well as the concept of grain size and grain morphology. I explore the scattering optics of snow through hyperspectral directional reflectance measurements from the Automated Spectro-Goniometer over clean snow, field measurements of snow spectral albedo and directional reflectance from dust-laden and soot-laden snow, field measurements of snow directional reflectance from wet snow, field measurements of snow directional reflectance from algal snow (Chlamydomonas nivalis), and stratigraphy of grain size (specific surface area) from contact spectroscopy and the use of this stratigraphy in driving radiative transfer modeling of snow spectral albedo. Our improved understanding of terrestrial snow cover then expands our capacity to more quantitatively explore the geology and biology of planetary icy worlds.