Comparison of different methods to retrieve optical-equivalent snow grain size in central Antarctica
The optical-equivalent snow grain size affects the reflectivity of snow surfaces and, thus, the local surface energy budget in particular in polar regions. Therefore, the specific surface area (SSA), from which the optical snow grain size is derived, was observed for a 2-month period in central...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2017-11-01
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| Series: | The Cryosphere |
| Online Access: | https://www.the-cryosphere.net/11/2727/2017/tc-11-2727-2017.pdf |
| _version_ | 1811241399446667264 |
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| author | T. Carlsen G. Birnbaum A. Ehrlich J. Freitag G. Heygster L. Istomina S. Kipfstuhl A. Orsi M. Schäfer M. Wendisch |
| author_facet | T. Carlsen G. Birnbaum A. Ehrlich J. Freitag G. Heygster L. Istomina S. Kipfstuhl A. Orsi M. Schäfer M. Wendisch |
| author_sort | T. Carlsen |
| collection | DOAJ |
| description | The optical-equivalent snow grain size affects the reflectivity of snow
surfaces and, thus, the local surface energy budget in particular in polar
regions. Therefore, the specific surface area (SSA), from which the optical
snow grain size is derived, was observed for a 2-month period in central
Antarctica (Kohnen research station) during austral summer 2013/14. The data
were retrieved on the basis of ground-based spectral surface albedo
measurements collected by the COmpact RAdiation measurement System (CORAS)
and airborne observations with the Spectral Modular Airborne Radiation
measurement sysTem (SMART). 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 in order to reduce the impact of the solar zenith angle on the
retrieval results and to cover measurements in overcast conditions. Spectral
ratios of surface albedo at 1280 and 1100 nm wavelength were used to
reduce the retrieval uncertainty. The retrieval was applied to the
ground-based and airborne observations and validated against optical in situ
observations of SSA utilizing an IceCube device. The SSA retrieved from CORAS
observations varied between 27 and 89 m<sup>2</sup> kg<sup>−1</sup>. Snowfall events
caused distinct relative maxima of the SSA which were followed by a gradual
decrease in SSA due to snow metamorphism and wind-induced transport of
freshly
fallen ice crystals. The ability of the modified algorithm to include
measurements in overcast conditions improved the data coverage, in particular at
times when precipitation events occurred and the SSA changed quickly. SSA
retrieved from measurements with CORAS and MODIS agree with the in situ
observations within the ranges given by the measurement uncertainties.
However, SSA retrieved from the airborne SMART data slightly underestimated
the ground-based results. |
| first_indexed | 2024-04-12T13:34:40Z |
| format | Article |
| id | doaj.art-823d96a68dd3405f9544c56629b04ada |
| institution | Directory Open Access Journal |
| issn | 1994-0416 1994-0424 |
| language | English |
| last_indexed | 2024-04-12T13:34:40Z |
| publishDate | 2017-11-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | The Cryosphere |
| spelling | doaj.art-823d96a68dd3405f9544c56629b04ada2022-12-22T03:31:02ZengCopernicus PublicationsThe Cryosphere1994-04161994-04242017-11-01112727274110.5194/tc-11-2727-2017Comparison of different methods to retrieve optical-equivalent snow grain size in central AntarcticaT. Carlsen0G. Birnbaum1A. Ehrlich2J. Freitag3G. Heygster4L. Istomina5S. Kipfstuhl6A. Orsi7M. Schäfer8M. Wendisch9Leipzig Institute for Meteorology, University of Leipzig, Leipzig, GermanyAlfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, GermanyLeipzig Institute for Meteorology, University of Leipzig, Leipzig, GermanyAlfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, GermanyInstitute of Environmental Physics, University of Bremen, Bremen, GermanyInstitute of Environmental Physics, University of Bremen, Bremen, GermanyAlfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, GermanyLaboratoire des Sciences du Climat et de l'Environnement, Gif-sur-Yvette, FranceLeipzig Institute for Meteorology, University of Leipzig, Leipzig, GermanyLeipzig Institute for Meteorology, University of Leipzig, Leipzig, GermanyThe optical-equivalent snow grain size affects the reflectivity of snow surfaces and, thus, the local surface energy budget in particular in polar regions. Therefore, the specific surface area (SSA), from which the optical snow grain size is derived, was observed for a 2-month period in central Antarctica (Kohnen research station) during austral summer 2013/14. The data were retrieved on the basis of ground-based spectral surface albedo measurements collected by the COmpact RAdiation measurement System (CORAS) and airborne observations with the Spectral Modular Airborne Radiation measurement sysTem (SMART). 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 in order to reduce the impact of the solar zenith angle on the retrieval results and to cover measurements in overcast conditions. Spectral ratios of surface albedo at 1280 and 1100 nm wavelength were used to reduce the retrieval uncertainty. The retrieval was applied to the ground-based and airborne observations and validated against optical in situ observations of SSA utilizing an IceCube device. The SSA retrieved from CORAS observations varied between 27 and 89 m<sup>2</sup> kg<sup>−1</sup>. Snowfall events caused distinct relative maxima of the SSA which were followed by a gradual decrease in SSA due to snow metamorphism and wind-induced transport of freshly fallen ice crystals. The ability of the modified algorithm to include measurements in overcast conditions improved the data coverage, in particular at times when precipitation events occurred and the SSA changed quickly. SSA retrieved from measurements with CORAS and MODIS agree with the in situ observations within the ranges given by the measurement uncertainties. However, SSA retrieved from the airborne SMART data slightly underestimated the ground-based results.https://www.the-cryosphere.net/11/2727/2017/tc-11-2727-2017.pdf |
| spellingShingle | T. Carlsen G. Birnbaum A. Ehrlich J. Freitag G. Heygster L. Istomina S. Kipfstuhl A. Orsi M. Schäfer M. Wendisch Comparison of different methods to retrieve optical-equivalent snow grain size in central Antarctica The Cryosphere |
| title | Comparison of different methods to retrieve optical-equivalent snow grain size in central Antarctica |
| title_full | Comparison of different methods to retrieve optical-equivalent snow grain size in central Antarctica |
| title_fullStr | Comparison of different methods to retrieve optical-equivalent snow grain size in central Antarctica |
| title_full_unstemmed | Comparison of different methods to retrieve optical-equivalent snow grain size in central Antarctica |
| title_short | Comparison of different methods to retrieve optical-equivalent snow grain size in central Antarctica |
| title_sort | comparison of different methods to retrieve optical equivalent snow grain size in central antarctica |
| url | https://www.the-cryosphere.net/11/2727/2017/tc-11-2727-2017.pdf |
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