Preprints
https://doi.org/10.5194/tc-2021-53
https://doi.org/10.5194/tc-2021-53

  01 Mar 2021

01 Mar 2021

Review status: this preprint is currently under review for the journal TC.

Experimental and model-based investigation of the links between snow bidirectional reflectance and snow microstructure

Marie Dumont1, Frederic Flin1, Aleksey Malinka2, Olivier Brissaud3, Pascal Hagenmuller1, Philippe Lapalus1, Bernard Lesaffre1, Anne Dufour1, Neige Calonne1, Sabine Rolland du Roscoat4, and Edward Ando4 Marie Dumont et al.
  • 1Univ. Grenoble Alpes, Université de Toulouse, Météo-France, CNRS, CNRM, Centre d’Études de la Neige, 38000 Grenoble, France
  • 2Institute of Physics, National Academy of Sciences of Belarus, Minsk, Belarus
  • 3Univ. Grenoble Alpes - CNRS, IPAG, Grenoble, France
  • 4UGA - Grenoble INP - CNRS, 3SR UMR 5521, Grenoble, France

Abstract. Snow stands out from materials at the Earth's surface owing to its unique optical properties. Snow optical properties are sensitive to the snow microstructure, triggering potent climate feedbacks. The impacts of snow microstructure on its optical properties such as reflectance are, to date, only partially understood. However, precise modelling of snow reflectance, particularly bidirectional one, are required in many problems, e.g. to process correctly satellite data over snow-covered areas. This study presents a dataset that combines bidirectional reflectance measurements over 500–2500 nm and the X-ray tomography of the snow microstructure for three snow samples of two different morphological types. The dataset is used to evaluate the stereological approach from Malinka (2014) that relates snow optical properties to the chord length distribution in the snow microstructure. The mean chord length and SSA retrieved with this approach from the albedo spectrum and those measured by the X-ray tomography are in excellent agreement. The analysis of the 3D images has shown that the random chords of the ice phase obey the gamma distribution with the shape parameter m taking the value approximately equal or a little greater than 2. For weak and intermediate absorption (high and medium albedo), the simulated bidirectional reflectances reproduce the measured ones accurately but tend to slightly overestimate the anisotropy of the radiation. For such absorptions the use of the exponential law for the ice chord length distribution instead of the one measured with the X-ray tomography does not affect the simulated reflectance. In contrast, under high absorption (albedo of a few percent), snow microstructure and especially facet orientation at the surface, plays a significant role for the reflectance, particularly at oblique viewing and incidence.

Marie Dumont et al.

Status: open (until 26 Apr 2021)

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Marie Dumont et al.

Marie Dumont et al.

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Short summary
The role of snow microstructure on snow optical properties is only partially understood despite the importance of snow optical properties for the Earth system. We presents a dataset combining bidirectional reflectance measurements and 3D images of snow. We show that the snow reflectance is adequately simulated using the distribution of the ice chord lengths in the snow microstructure and that the impact of the morphological type of snow is especially important when ice is highly absorptive.