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| Titel |
Analysis of snow bidirectional reflectance from ARCTAS Spring-2008 Campaign |
| VerfasserIn |
A. Lyapustin, C. K. Gatebe, R. Kahn, R. Brandt, J. Redemann, P. Russell, M. D. King, C. A. Pedersen, S. Gerland, R. Poudyal, A. Marshak, Y. Wang, C. Schaaf, D. Hall, A. Kokhanovsky |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 10, no. 9 ; Nr. 10, no. 9 (2010-05-10), S.4359-4375 |
| Datensatznummer |
250008433
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| Publikation (Nr.) |
 copernicus.org/acp-10-4359-2010.pdf |
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| Zusammenfassung |
| The spring 2008 Arctic Research of the Composition of the
Troposphere from Aircraft and Satellites (ARCTAS) experiment was one of
major intensive field campaigns of the International Polar Year aimed at
detailed characterization of atmospheric physical and chemical processes in
the Arctic region. A part of this campaign was a unique snow bidirectional
reflectance experiment on the NASA P-3B aircraft conducted on 7 and 15 April
by the Cloud Absorption Radiometer (CAR) jointly with airborne Ames Airborne
Tracking Sunphotometer (AATS) and ground-based Aerosol Robotic Network
(AERONET) sunphotometers. The CAR data were atmospherically corrected to
derive snow bidirectional reflectance at high 1° angular resolution in
view zenith and azimuthal angles along with surface albedo. The derived
albedo was generally in good agreement with ground albedo measurements
collected on 15 April. The CAR snow bidirectional reflectance factor (BRF)
was used to study the accuracy of analytical Ross-Thick Li-Sparse (RTLS),
Modified Rahman-Pinty-Verstraete (MRPV) and Asymptotic Analytical Radiative
Transfer (AART) BRF models. Except for the glint region (azimuthal angles
φ<40°), the best fit MRPV and RTLS models fit snow BRF to
within ±0.05. The plane-parallel radiative transfer (PPRT) solution was
also analyzed with the models of spheres, spheroids, randomly oriented
fractal crystals, and with a synthetic phase function. The latter merged the
model of spheroids for the forward scattering angles with the fractal model
in the backscattering direction. The PPRT solution with synthetic phase
function provided the best fit to measured BRF in the full range of angles.
Regardless of the snow grain shape, the PPRT model significantly
over-/underestimated snow BRF in the glint/backscattering regions,
respectively, which agrees with other studies. To improve agreement with
experiment, we introduced a model of macroscopic snow surface roughness by
averaging the PPRT solution over the slope distribution function and by
adding a simple model of shadows. With macroscopic roughness described by
two parameters, the AART model achieved an accuracy of about ±0.05 with
a possible bias of ±0.03 in the spectral range 0.4–2.2 μm. This
high accuracy holds at view zenith angles below 55–60° covering the
practically important range for remote sensing applications, and includes
both glint and backscattering directions. |
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