期刊名称：ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences
印刷版ISSN：2194-9042
电子版ISSN：2194-9050
出版年度：2007
卷号：XXXVI-7/C50
出版社：Copernicus Publications
摘要：We present a technique for in situ measurement of the vertical and spatial stratigraphic distribution of snowoptical grain size with a coupled contact illumination probe and field spectroradiometer. Accurate measurements ofoptically equivalent grain size are critical for modeling of radiative properties of snow such as spectral albedo andmicrowave emission. Here, we refer to grain size inferred from traditional hand lens measurements as TGR(traditional grain radius) and optically equivalent grain radius as OGR (optical grain radius). Given the subjectivenature of TGR measurements, it is a poorly defined and as such is not repeatable from observer to observer (S.Colbeck, personal communication). The OGR is well defined as the spherical grain radius required to give the samespectral or spectrally-integrated albedo. OGR may also be represented by the specific surface area (surface area perunit volume ice ) for the case of fluxes or albedo for snow or clouds.Measurements of the spectral reflectance of the snowpit surface are made at 2 cm intervals in the vertical planeunder constant illumination and view geometries. We invert the integral of the continuum normalization of the iceabsorption feature with maximum at 1.03 μm wavelength for optically equivalent grain size using the validatedmodel of Nolin and Dozier (2000) that has accuracy of ±50-100 μm across the grain size range 50 to 900 μm.Results are presented for an alpine site in southwest Colorado across the ablation season and for a Greenland icesheet site at the onset of snowmelt. These results suggest that only for rounded grains are traditional measurementsof grain size from hand lens nearly accurate (R2= 0.4, RMSE = 160 μm) for estimating optical grain radius,whereas for polycrystals and faceted grains the hand lens approach is strongly inaccurate (R2= 0.03 and 0.24,RMSE = 1206 and 1010 μm, respectively). We demonstrate the order of magnitude improvement in modeling ofshortwave spectral albedo and net shortwave flux with contact spectroscopy measurements of grain size stratigraphy
