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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Volume 10, issue 6
The Cryosphere, 10, 2655-2672, 2016
https://doi.org/10.5194/tc-10-2655-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
The Cryosphere, 10, 2655-2672, 2016
https://doi.org/10.5194/tc-10-2655-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 14 Nov 2016

Research article | 14 Nov 2016

Refinement of the ice absorption spectrum in the visible using radiance profile measurements in Antarctic snow

Ghislain Picard1,2, Quentin Libois1,a, and Laurent Arnaud1 Ghislain Picard et al.
  • 1UGA/CNRS, Laboratoire de Glaciologie et Géophysique de l'Environnement (LGGE) – UMR5183, 38041 Grenoble, France
  • 2ACE CRC, University of Tasmania, Private Bag 80, Hobart, TAS 7001, Australia
  • anow at: Department of Earth and Atmospheric Sciences, Université du Québec à Montréal (UQAM), Montréal, Canada

Abstract. Ice is a highly transparent material in the visible. According to the most widely used database (IA2008; Warren and Brandt, 2008), the ice absorption coefficient reaches values lower than 10−3m−1 around 400nm. These values were obtained from a vertical profile of spectral radiance measured in a single snow layer at Dome C in Antarctica. We reproduced this experiment using an optical fiber inserted in the snow to record 56 profiles from which 70 homogeneous layers were identified. Applying the same estimation method on every layer yields 70 ice absorption spectra. They present a significant variability but absorption coefficients are overall larger than IA2008 by 1 order of magnitude at 400–450nm. We devised another estimation method based on Bayesian inference that treats all the profiles simultaneously. It reduces the statistical variability and confirms the higher absorption, around 2 × 10−2m−1 near the minimum at 440nm. We explore potential instrumental artifacts by developing a 3-D radiative transfer model able to explicitly account for the presence of the fiber in the snow. The simulation shows that the radiance profile is indeed perturbed by the fiber intrusion, but the error on the ice absorption estimate is not larger than a factor of 2. This is insufficient to explain the difference between our new estimate and IA2008. The same conclusion applies regarding the plausible contamination by black carbon or dust, concentrations reported in the literature are insufficient. Considering the large number of profiles acquired for this study and other estimates from the Antarctic Muon and Neutrino Detector Array (AMANDA), we nevertheless estimate that ice absorption values around 10−2m−1 at the minimum are more likely than under 10−3m−1. A new estimate in the range 400–600nm is provided for future modeling of snow, cloud, and sea-ice optical properties. Most importantly, we recommend that modeling studies take into account the large uncertainty of the ice absorption coefficient in the visible and that future estimations of the ice absorption coefficient should also thoroughly account for the impact of the measurement method.

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The absorption of visible light in ice is very weak but its precise value is unknown. By measuring the profile of light intensity in snow, Warren and Brand (2006) deduced that light is attenuated by a factor 2 per kilometer in pure ice at a wavelength of 400 nm. We replicated their experiment on a large number of samples and found that ice absorption is at least 10 times stronger. The paper explores various potential physical and statistical biases that could impact the experiment.
The absorption of visible light in ice is very weak but its precise value is unknown. By...
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