Journal cover Journal topic
The Cryosphere An interactive open-access journal of the European Geosciences Union
doi:10.5194/tc-2016-294
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
01 Feb 2017
Review status
This discussion paper is under review for the journal The Cryosphere (TC).
Comparison of different methods to retrieve effective snow grain size in central Antarctica
Tim Carlsen1, Gerit Birnbaum2, André Ehrlich1, Johannes Freitag2, Georg Heygster3, Larysa Istomina3, Sepp Kipfstuhl2, Anaïs Orsi4, Michael Schäfer1, and Manfred Wendisch1 1Leipzig Institute for Meteorology, Leipzig University, Leipzig, Germany
2Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
3Institute of Environmental Physics, University of Bremen, Bremen, Germany
4Laboratoire des Sciences du Climat et de l’Environnement, Gif-sur-Yvette, France
Abstract. The effective size of snow grains (reff) affects the reflectivity of snow surfaces and thus the local surface energy budget in particular in polar regions. Therefore, the specific surface area (SSA) was monitored for a two-month period in central Antarctica (Kohnen research station) during austral summer 2013/14. The data were retrieved on the basis of spectral surface albedo measurements collected by the COmpact RAdiation measurement System (CORAS, ground-based) and the Spectral Modular Airborne Radiation measurement sysTem (SMART, airborne). The Snow Grain Size and Pollution amount (SGSP) algorithm, originally developed to analyze spaceborne reflectance measurements by the MODerate Resolution Imaging Spectroradiometer (MODIS), was modified and applied to the ground-based and airborne observations collected in this study. Furthermore, spectral ratios of surface albedo at 1280 nm and 1100 nm wavelength were used to reduce the retrieval uncertainty. Additionally, the algorithm originally developed for cloudless conditions was adapted to handle overcast conditions. Optical in situ observations of SSA utilizing an IceCube device were used to validate the retrieval results. The SSA retrieved from CORAS observations varied between 27 m2 kg-1 and 86 m2 kg-1. Snowfall events caused distinct SSA maxima which were often followed by a gradual decrease in SSA due to snow metamorphism and wind-induced transport of fresh fallen ice crystals (vice versa for reff). SSA retrieved by data from CORAS and MODIS agree with the in situ observations within the ranges given by the measurement uncertainties. However, SSA retrieved by the airborne SMART observations underestimated the ground-based observations by a factor of 2.1 (overestimation of reff).

Citation: Carlsen, T., Birnbaum, G., Ehrlich, A., Freitag, J., Heygster, G., Istomina, L., Kipfstuhl, S., Orsi, A., Schäfer, M., and Wendisch, M.: Comparison of different methods to retrieve effective snow grain size in central Antarctica, The Cryosphere Discuss., doi:10.5194/tc-2016-294, in review, 2017.
Tim Carlsen et al.
Tim Carlsen et al.
Tim Carlsen et al.

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Short summary
The effective size of snow grains (reff) affects the reflectivity of snow surfaces and thus the local surface energy budget in particular in polar regions. The temporal evolution of reff retrieved from ground-based, airborne, and spaceborne remote sensing could reproduce optical in situ measurements for a two-month period in central Antarctica (2013/14). The presented validation study provided a unique testbed for retrievals of reff under Antarctic conditions where in situ data are scarce.
The effective size of snow grains (reff) affects the reflectivity of snow surfaces and thus the...
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