 |
| Titel |
Influence of spatial heterogeneity of local surface albedo on the area-averaged surface albedo retrieved from airborne irradiance measurements |
| VerfasserIn |
E. Jäkel, M. Wendisch, B. Mayer |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1867-1381
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 6, no. 3 ; Nr. 6, no. 3 (2013-03-01), S.527-537 |
| Datensatznummer |
250017829
|
| Publikation (Nr.) |
 copernicus.org/amt-6-527-2013.pdf |
|
|
|
|
|
| Zusammenfassung |
| Spectral airborne upward and downward irradiance measurements are
used to derive the area-averaged surface albedo. Real surfaces are
not homogeneous in their reflectivity. Therefore, this work studies
the effects of the heterogeneity of surface reflectivity on the
area-averaged surface albedo to quantify how well aircraft
measurements can resolve the small-scale variability of the local
surface albedo. For that purpose spatially heterogeneous surface
albedo maps were input into a 3-dimensional (3-D) Monte Carlo
radiative transfer model to simulate 3-D irradiance fields. The
calculated up- and downward irradiances in altitudes between 0.1
and 5 km are used to derive the area-averaged surface albedo using
an iterative retrieval method that removes the effects due to
atmospheric scattering and absorption within the layer beneath the
considered level. For the case of adjacent land and sea surfaces,
parametrizations are presented which quantify the horizontal
distance from the coastline that is required to reduce surface
heterogeneity effects on the area-averaged surface albedo to a given
limit. The parametrization which is a function of altitude, aerosol
optical depth, single scattering albedo, and the ratio of local land
and sea albedo was applied for airborne spectral measurements. In
addition, the deviation between area-averaged and local surface
albedo is determined for more complex surface albedo maps. For
moderate aerosol conditions (optical depth less than 0.4) and a
wavelength range between 400 and 1000 nm, the altitude and the
heterogeneity of the surface albedo are the dominant factors
determining the mean deviation between local and area-averaged
surface albedo. A parametrization of the mean deviation is applied
to an albedo map that was derived from a Landsat image of an area in
East Anglia (UK). Parametrization and direct comparison of local and
area-averaged surface albedo show similar mean deviations (20% vs. 25%)
over land. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|