Aerosol properties over the SAFARI-2000 area retrieved from ATSR-2

摘要

The aerosol optical depth (AOD) at three wavelengths has been retrieved from the radiance measured at the top of the atmosphere (TOA) by the ATSR-2 (Along Track Scanning Radiometer) during the SAFARI-2000 (Southern African Regional Science Initiative) dry season field campaign from 1 August to 30 September 2000. Two aerosol types were implemented in the ATSR-2 retrieval algorithm: a highly absorbing aerosol that is mainly due to biomass burning and a less absorbing mixture of biomass burning, anthropogenic and biogenic aerosols. The mixing ratio of these two aerosol types was determined by comparison of the two modeled aerosol types with the ATSR-2 measured signal. The accuracy of the AOD values determined from the ATSR-2 data is 0.08 ± 0.06 for August and 0.14 ± 0.13 for September, as determined from comparison with various AERONET Sun photometers located in the area. In August 2000, the highly absorbing aerosol was the major aerosol component retrieved over the North-Western part of the SAFARI-2000 area. AOD values of up to 0.8 and ?ngstr?m coefficients of up to 2.1 were observed. Further to the South, the less absorbing type dominated with AOD values of up to 0.3 over the central SAFARI-2000 area. During September the meteorological situation changed and the high absorbing aerosols were observed further South, due to advective transport of aerosol over a wider area. AOD values were up to 1 with ?ngstr?m coefficients similar to those in August. Low absorbing aerosols were observed over a relatively small area. Over the Namibian and Kalahari deserts dust emissions caused high AOD values of up to 0.75 during both months.