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| Titel |
Deriving albedo maps for HAPEX-Sahel from ASAS data using kernel-driven BRDF models |
| VerfasserIn |
P. Lewis, M. I. Disney, M. J. Barnsley, J.-P. Muller |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 3, no. 1 ; Nr. 3, no. 1, S.1-11 |
| Datensatznummer |
250000751
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| Publikation (Nr.) |
 copernicus.org/hess-3-1-1999.pdf |
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| Zusammenfassung |
This paper describes the application and testing of a method
for deriving spatial estimates of albedo from multi-angle remote sensing data. Linear
kernel-driven models of surface bi-directional reflectance have been inverted against high
spatial resolution multi-angular, multi- spectral airborne data of the principal cover
types within the HAPEX-Sahel study site in Niger, West Africa. The airborne data are
obtained from the NASA Airborne Solid-state Imaging Spectrometer (ASAS) instrument, flown
in Niger in September and October 1992. The maps of model parameters produced are used to
estimate integrated reflectance properties related to spectral albedo. Broadband albedo
has been estimated from this by weighting the spectral albedo for each pixel within the
map as a function of the appropriate spectral solar irradiance and proportion of direct
and diffuse illumination.
Partial validation of the results was performed by comparing
ASAS reflectance and derived directional-hemispherical reflectance with simulations of a
millet canopy made with a complex geometric canopy reflectance model, the Botanical Plant
Modelling System (BPMS). Both were found to agree well in magnitude. Broadband albedo
values derived from the ASAS data were compared with ground-based (point sample) albedo
measurements and found to agree extremely well. These results indicate that the linear
kernel-driven modelling approach, which is to be used operationally to produce global 16
day, 1 km albedo maps from forthcoming NASA Earth Observing System spaceborne data, is
both sound and practical for the estimation of angle-integrated spectral reflectance
quantities related to albedo. Results for broadband albedo are dependent on spectral
sampling and on obtaining the correct spectral weigthings. |
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