Contact spectroscopy for determination of stratigraphy of snow optical grain size
Authors: Painter, Thomas H.; Molotch, Noah P.; Cassidy, Maureen; Flanner, Mark; Steffen, Konrad
Source: Journal of Glaciology, Volume 53, Number 180, January 2007 , pp. 121-127(7)
Publisher: International Glaciological Society
Abstract:We present a technique for in situ measurement of the vertical and spatial stratigraphic distribution of snow optical grain size with a coupled contact illumination probe and field spectroradiometer. Accurate measurements of optical-equivalent grain size are critical for modeling radiative properties of snow such as spectral albedo and microwave emission. Measurements of the spectral reflectance of the snow-pit surface are made at 2 cm intervals in the vertical plane under constant illumination and view geometries. We invert the integral of the continuum normalization of the ice absorption feature with maximum at 1.03 m wavelength for optical-equivalent grain size using the validated model of Nolin and Dozier (2000) that has accuracy of ±10–50 m across the grain-size range 50–900 m. Results are presented for an alpine site in southwest Colorado, USA, across the ablation season and for a Greenland ice-sheet site at the onset of snowmelt. These results suggest that traditional measurements of grain size using a hand lens are nearly accurate only for rounded grains (R2 = 0.41, rmse = 160 m); for polycrystals and faceted grains the hand-lens approach is very inaccurate (R2 = 0.03 and 0.24, rmse = 1206 and 1010 m, respectively). We demonstrate an order-of-magnitude improvement in modeling of shortwave spectral albedo and net shortwave flux with contact spectroscopy measurements of grain-size stratigraphy over those from a hand lens.
Document Type: Research Article
Publication date: 2007-01-01
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