 |
| Titel |
Albedo over rough snow and ice surfaces |
| VerfasserIn |
S. Lhermitte, J. Abermann, C. Kinnard |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1994-0416
|
| Digitales Dokument |
URL |
| Erschienen |
In: The Cryosphere ; 8, no. 3 ; Nr. 8, no. 3 (2014-06-23), S.1069-1086 |
| Datensatznummer |
250116167
|
| Publikation (Nr.) |
 copernicus.org/tc-8-1069-2014.pdf |
|
|
|
|
|
| Zusammenfassung |
Both satellite and ground-based broadband albedo measurements over rough and
complex terrain show several limitations concerning feasibility and
representativeness. To assess these limitations and understand the effect of
surface roughness on albedo, firstly, an intrasurface radiative transfer
(ISRT) model is combined with albedo measurements over different penitente
surfaces on Glaciar Tapado in the semi-arid Andes of northern Chile. Results
of the ISRT model show effective albedo reductions over the penitentes up to
0.4 when comparing the rough surface albedo relative to the albedo of the flat
surface. The magnitude of these reductions primarily depends on the opening
angles of the penitentes, but the shape of the penitentes and spatial
variability of the material albedo also play a major role.
Secondly, the ISRT model is used to reveal the effect of using albedo
measurements at a specific location (i.e., apparent albedo) to infer the true
albedo of a penitente field (i.e., effective albedo). This effect is
especially strong for narrow penitentes, resulting in sampling biases of up to
±0.05. The sampling biases are more pronounced when the sensor is low
above the surface, but remain relatively constant throughout the day.
Consequently, it is important to use a large number of samples at various
places and/or to locate the sensor sufficiently high in order to avoid this
sampling bias of surface albedo over rough surfaces.
Thirdly, the temporal evolution of broadband albedo over a penitente-covered
surface is analyzed to place the experiments and their uncertainty into a
longer temporal context. Time series of albedo measurements at an automated
weather station over two ablation seasons reveal that albedo decreases early
in the ablation season. These decreases stabilize from February onwards with
variations being caused by fresh snowfall events. The 2009/2010 and
2011/2012 seasons differ notably, where the latter shows lower albedo values
caused by larger penitentes. Finally, a comparison of the ground-based albedo
observations with Landsat and MODIS (Moderate Resolution Imaging Spectroradiometer)-derived albedo showed that both satellite
albedo products capture the albedo evolution with root mean square errors of
0.08 and 0.15, respectively, but also illustrate their shortcomings related
to temporal resolution and spatial heterogeneity over small mountain
glaciers. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|