In situ continuous visible and near-infrared spectroscopy of an alpine snowpack
The Cryosphere Discussions
Snow spectral albedo in the visible/near-infrared range has been continuously measured during a winter season at Col de Porte alpine site (French Alps, 45.30&deg;&thinsp;N, 5.77&deg;&thinsp;E, 1325&thinsp;m&thinsp;a.s.l.). The evolution of such alpine snowpack is complex due to intensive precipitation, rapid melt events and Saharan dust deposition outbreaks. This study highlights that the resulting intricated variations of spectral albedo can be successfully explained by
... sfully explained by variations of the following snow surface variables&thinsp;:&thinsp;snow specific surface area (SSA), effective light-absorbing impurities content, presence of liquid water and slope. The methodology developped in this study disantangles the effect of these parameters on snow spectral albedo. The presence of liquid water at the snow surface results in a spectral shift of the albedo from which melt events can be identified with an occurence of false detection rate lower than 3.5&thinsp;%. Snow SSA mostly impacts spectral albedo in the near-infrared range. Impurity deposition mostly impacts the albedo in the visible range but this impact is very dependent on snow SSA and surface slope. Our work thus demonstrates that the SSA estimation from spectral albedo is affected by large uncertainties for a tilted snow surface and medium to high impurity contents and that the estimation of impurity content is also affected by large uncertainties, especially for low values below 50&thinsp;ng&thinsp;g<sup>&minus;1</sup> black carbon equivalent. The proposed methodology opens routes for retrieval of SSA, impurity content, melt events and surface slope from spectral albedo. However, an exhaustive accuracy assessment of the snow parameters retrieval would require more independent in situ measurements and is beyond the scope of the present study. Such time series of snow spectral albedo nevertheless already provides a new insight into our understanding of the evolution of snow surface properties.