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| Titel |
Measurements and modelling of snow particle size and shortwave infrared albedo over a melting Antarctic ice sheet |
| VerfasserIn |
R. Pirazzini, P. Räisänen, T. Vihma, M. Johansson, E.-M. Tastula |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1994-0416
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| Digitales Dokument |
URL |
| Erschienen |
In: The Cryosphere ; 9, no. 6 ; Nr. 9, no. 6 (2015-12-15), S.2357-2381 |
| Datensatznummer |
250116885
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| Publikation (Nr.) |
 copernicus.org/tc-9-2357-2015.pdf |
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| Zusammenfassung |
| The albedo of a snowpack depends on the single-scattering properties of
individual snow crystals, which have a variety of shapes and sizes, and are
often bounded in clusters. From the point of view of optical modelling, it
is essential to identify the geometric dimensions of the population of snow
particles that synthesize the scattering properties of the snowpack surface.
This involves challenges related to the complexity of modelling the
radiative transfer in such an irregular medium, and to the difficulty of
measuring microphysical snow properties. In this paper, we illustrate a
method to measure the size distribution of a snow particle parameter, which
roughly corresponds to the smallest snow particle dimension, from
two-dimensional macro photos of snow particles taken in Antarctica at the
surface layer of a melting ice sheet. We demonstrate that this snow particle
metric corresponds well to the optically equivalent effective radius
utilized in radiative transfer modelling, in particular when snow particles
are modelled with the droxtal shape. The surface albedo modelled on the
basis of the measured snow particle metric showed an excellent match with
the observed albedo when there was fresh or drifted snow at the surface. In
the other cases, a good match was present only for wavelengths longer than
1.4 μm. For shorter wavelengths, our modelled albedo generally
overestimated the observations, in particular when surface hoar and faceted
polycrystals were present at the surface and surface roughness was increased
by millimetre-scale cavities generated during melting. Our results indicate
that more than just one particle metric distribution is needed to
characterize the snow scattering properties at all optical wavelengths, and
suggest an impact of millimetre-scale surface roughness on the shortwave
infrared albedo. |
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