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UP: Umweltphysik

UP 5: Atmosphäre und Klima

UP 5.5: Talk

Monday, March 18, 2002, 15:15–15:30, HS 11

SPACE-BORNE DETERMINATION OF AEROSOL OPTICAL THICKNESS OVER LAND SURFACES — •Wolfgang von Hoyningen-Huene, Martin Freitag, John, P. Burrows, , , and — Institute of Environmental Physics, University of Bremen

Climate research and environmental control require quantitative information on spatial and temporal impact of atmospheric aerosol. This task only can be solved by space-borne observations. Modern multi-channel space-borne radiometers (SeaWiFS, MERIS, MODIS, SCIAMACHY et al.) provide sufficient spectral and spatial information to recognize aerosol effects from satellite observations and to quantify aerosol impacts in the environment in terms of an aerosol optical thickness (AOT).
Over land surfaces, the surface is heterogeneous, the reflectances are higher and more variable, however the reflectance decrease with decreasing wavelength, especially, if the surface is covered with vegetation.
The used method subtracts known effects as Rayleigh path reflectance using a digital elevation model and estimations of an apparent surface reflectance using the NDVI to obtain an aerosol reflectance for the entire retrieval of the AOT by look-up-tables (LUT).
This approach removes more or less completely the variability caused by different vegetation cover and surface elevation and gives the AOT for wavelength ≤ 0.67 µ m within a 20 % range. The method is applied successfully with SeaWiFS L1b data during closure experiments as LACE-98 in Germany and INDOEX.