Aerosol retrievals from METEOSAT-8 - CM SAF

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SAF on Climate Monitoring Visiting Scientists Report Doc. No: 1.0 Issue : 1.0 Date : 4 October 2006 Figure 2: Example of Aerosol Optical Thickness level 2 product over land at 865 nm from the POLDER-PARASOL instrument on 13 th of July 2005. (source: ICARE web server http://wwwicare.univ-lille1.fr/) Figure 3: Example of the daily aerosol optical thickness product over land and ocean derived from MODIS Aqua - 12 -
SAF on Climate Monitoring Visiting Scientists Report Doc. No: 1.0 Issue : 1.0 Date : 4 October 2006 Figure 4: Example of the daily aerosol optical thickness product derived from MISR on 14 th of July 2005. The colour scale ranges from 0 to 0.5. source: EOS LARC MISR web server 5.1.3 GOES The GOES Aerosol-Smoke Product (GASP) provides aerosol optical depth retrievals over the U.S. at 4 km spatial resolution and 30 minute intervals. The retrieval is performed over ocean and land and is available once per day for the full disk of the Earth from GOES-East (providing information for South America). The algorithm is described in Knapp et al. (2002, 2005). The main approach is to build a surface reflectance reference by selecting, for each pixel, the second darkest image in the composite time period and then to perform aerosol retrieval over land based on Look Up Tables of gaseous and Rayleigh corrected reflectance for various surface reflectance and aerosol loading (see an example of the AOT map over the US East coast for the 19 April 2005 in Fig. 5). The second darkest pixel is chosen to reduce the effect of cloud shadows (shadowed pixel reflectance is generally darker than surface -alone- reflectance). The reflectance reference is computed for a composite time period varying along the year from 7 days to 28 days. The length of the time period depends on the accuracy expected on the reflectance reference. More observations increase the chance of observing cloud-free and aerosol-free day, but if too many days of observations are used, the surface reflectance may change. For the eastern US, Knapp et al. found that 14-days period was a good compromise. The main limitation is that it requires that the TOA reflectances increase with increasing aerosol loading, and thus it does not work for a combination of bright surface and - 13 -
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Aerosol retrievals from METEOSAT-8 - CM SAF

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