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| Titel |
Snow spectral albedo at Summit, Greenland: measurements and numerical simulations based on physical and chemical properties of the snowpack |
| VerfasserIn |
C. M. Carmagnola, F. Domine, M. Dumont, P. Wright, B. Strellis, M. Bergin, J. Dibb, G. Picard, Q. Libois, L. Arnaud, S. Morin |
| 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 ; 7, no. 4 ; Nr. 7, no. 4 (2013-07-24), S.1139-1160 |
| Datensatznummer |
250017992
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| Publikation (Nr.) |
 copernicus.org/tc-7-1139-2013.pdf |
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| Zusammenfassung |
| The broadband albedo of surface snow is determined both by the near-surface
profile of the physical and chemical properties of the snowpack and by
the spectral and angular characteristics of the incident solar
radiation. Simultaneous measurements of the physical and chemical
properties of snow were carried out at Summit Camp, Greenland
(72°36´ N, 38°25´ W, 3210 m a.s.l.) in May
and June 2011, along with spectral albedo measurements. One of the
main objectives of the field campaign was to test our ability to
predict snow spectral albedo by comparing the measured albedo to the
albedo calculated with a radiative transfer model, using measured snow physical and chemical
properties. To achieve this goal, we made daily measurements of the snow spectral albedo in the
range 350–2200 nm and recorded snow stratigraphic information
down to roughly 80 cm. The snow specific surface area (SSA)
was measured using the DUFISSS instrument (DUal Frequency Integrating
Sphere for Snow SSA measurement, Gallet et al., 2009). Samples were
also collected for chemical analyses including black carbon (BC) and
dust, to evaluate the impact of light absorbing particulate
matter in snow. This is one of the most comprehensive albedo-related
data sets combining chemical analysis, snow physical properties and
spectral albedo measurements obtained in a polar environment. The
surface albedo was calculated from density, SSA, BC and dust profiles
using the DISORT model (DIScrete Ordinate Radiative Transfer, Stamnes et al., 1988) and
compared to the measured values. Results indicate that the energy absorbed by the
snowpack through the whole
spectrum considered can be inferred within 1.10%. This
accuracy is only slightly better than that which can be obtained
considering pure snow, meaning that the impact of impurities on the
snow albedo is small at Summit. In the near infrared, minor deviations in albedo up to 0.014
can be due to the accuracy of radiation and SSA measurements and to the surface
roughness, whereas deviations up to 0.05 can be explained by the spatial heterogeneity of
the snowpack at small scales, the assumption of spherical snow grains made for DISORT
simulations and the vertical resolution of measurements of surface layer physical properties.
At 1430 and around 1800 nm the discrepancies are larger and independent of the snow
properties; we propose that they are due to errors in the ice refractive index at these
wavelengths. This work contributes to the development of physically based albedo schemes
in detailed snowpack models, and to the improvement of retrieval
algorithms for estimating snow properties from remote sensing data. |
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