Retrieval of subpixel snow-covered area and grain size from imaging spectrometer data

Abstract

We describe and validate an automated model that retrieves subpixel snow-covered area and effective grain size from Airborne Visible/ Infrared Imaging Spectrometer (AVIRIS) data. The model analyzes multiple endmember spectral mixtures with a spectral library of snow, vegetation, rock, and soil. We derive snow spectral endmembers of varying grain size from a radiative transfer model; spectra for vegetation, rock, and soil were collected in the field and laboratory. For three AVIRIS images of Mammoth Mountain, California that span common snow conditions for winter through spring, we validate the estimates of snow-covered area with fine-resolution aerial photographs and validate the estimates of grain size with stereological analysis of snow samples collected within 2 h of the AVIRIS overpasses. The RMS error for snowcovered area retrieved from AVIRIS for the combined set of three images was 4%. The RMS error for snow grain size retrieved from a 3 Â 3 window of AVIRIS data for the combined set of three images is 48 Am, and the RMS error for reflectance integrated over the solar spectrum and over all hemispherical reflectance angles is 0.018. D

Impact of MODIS sensor calibration updates on Greenland Ice Sheet surface reflectance and albedo trends

“…Wet snow and ice areas on GrIS, in aggregate, still show coherent albedo decline across the nearly all visible and NIR wavelength bands from both sensors in C6 data (Tables 2, 3). Reduction in reflectance and albedo of this magnitude (several tenths) has been shown to result in radiative forcing of several tens of W m −2 (e.g., 0.4 broadband albedo decline from dust on snow resulting in 80 W m −2 radiative forcing, Painter et al, 2007;0.3 reduction in broadband visible albedo from black carbon and impurities on snow resulting in 70 W m −2 radiative forcing, Casey et al, 2017). The MODIS C6 reflectance and albedo data product results provide strong supporting evidence that enhanced melt processes (including melt-induced snow microstructure changes and melt-induced light-absorbing impurity accumulation changes) are creating an albedo feedback on the GrIS periphery.…”

“…We speculate that this signature could be evidence for substantial surface exposure and accumulation of mineral impurities in this region of GrIS. The spectra of most minerals exhibit higher NIR reflectance than bare ice, leading to the potential for a trend toward increased NIR albedo while visible albedo drops with high mineral content (Adams and Filice, 1967;Painter et al, 2003;Bøggild et al, 2010;Casey et al, 2012;Tedesco et al, 2013). The SE GrIS margin shows decreasing NIR albedo and only isolated change in visible wavelengths at the lowest elevations.…”

Snowpack radiative heating: Influence on Tibetan Plateau climate

“…The C experiments predict snow reflectance and absorption as in B, and allow solar absorption to occur realistically in sub-surface layers. Mean optically-effective snow grain sizes range from 50-1100 mm [e.g., Painter et al, 2003]. Experiments B and C predict snow radiative properties using a globally uniform snow radius r n = 200 mm.…”

The EnMAP Spaceborne Imaging Spectroscopy Mission for Earth Observation

“…The potential of airborne and spaceborne imaging spectrometers has long been exploited to monitor the Earth's surface and atmosphere and to provide valuable information for the better understanding of a large number of environmental processes (e.g., [3,4]). Those applications include, for example, vegetation monitoring and ecology (e.g., [5][6][7][8][9][10][11]), geology and soils (e.g., [12][13][14][15][16][17]), coastal and inland waters (e.g., [18][19][20][21]), mapping of snow properties [22,23] and archaeological prospection [24,25].…”