How robust are in-situ observations for validating satellite-derived albedo over the dark zone of the Greenland Ice Sheet?

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Type Article
Original languageEnglish
Pages (from-to)6218-6225
JournalGeophysical Research Letters
Volume44
Issue number12
Early online date22 Jun 2017
DOI
Publication statusE-pub ahead of print - 22 Jun 2017
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Abstract

Calibration and validation of satellite-derived ice sheet albedo data require high-quality, in-situ measurements commonly acquired by up- and down-facing pyranometers mounted on automated weather stations (AWS). However, direct comparison between ground and satellite-derived albedo can only be justified when the measured surface is homogeneous at the length-scale of both satellite pixel and in-situ footprint. Here, we use digital imagery acquired by an unmanned aerial vehicle to evaluate point-to-pixel albedo comparisons across the western, ablating margin of the Greenland Ice Sheet. Our results reveal that in-situ measurements overestimate albedo by up to 0.10 at the end of the melt-season because the ground footprints of AWS-mounted pyranometers are insufficient to capture the spatial heterogeneity of the ice surface as it progressively ablates and darkens. Statistical analysis of 21 AWS across the entire Greenland Ice Sheet reveals that almost half suffer from this bias, including some AWS located within the wet snow zone

Keywords

  • Albedo, Greenland Ice sheet, MODIS, automated weather stations, UAV, remote sensing