Aerosol retrievals from METEOSAT-8 - CM SAF

SAF on Climate Monitoring Visiting Scientists Report Doc. No: 1.0
Issue : 1.0
Date : 4 October 2006
corrected reflectance and the surface reflectance of reference such as:
R aer =R Ray_corrected -R surf_ref
In the second step we assume only single scattering and the aerosol type (and then phase function),
the aerosol optical thickness (AOT) is derived as follows:
AOT=Raer . 4 . cos(θs) cos(θv)/ P(Θ)
where: θs is the solar zenith angle, θv is the viewing zenith angle and P(Θ) is the value of the
aerosol phase function for the scattering angle Θ.
We assume a continental model with an Angstrom coefficient of 1.0, a real refractive index m r of
1.44 and an imaginary index mi of 0.0 which means there is no absorption (This aerosol model is
used in MERIS LUT's). Of course the single scattering assumption in the radiative transfer model
will lead to erroneous retrieval for large value of the AOT.
Fig. 10 resumes the schema of the retrieval method and Fig, 11 shows the aerosol optical thickness
at 670nm for the 14 th July 2005 over Europe and for every hour between 05:00 UTC and 18:00
UTC. The AOT maps are very noisy for partly cloudy areas as seen in Fig.11. Efforts must be
planned to use and apply a better cloud mask. However, the coverage is very good. An aerosol front
crossing the Pyrenees Mountains can be seen and be followed with correct land-sea continuity. A
dust event over North Africa is detected both over land and the Mediterranean Sea.
We also mapped the retrieved aerosol optical thickness over ocean assuming a Lambertian surface
with an albedo of 0.01 at 670nm. But, we plan in the near future to derive the sea reflectance with
the identical method used for the continental surface reflectance. In Appendix B maps of retrieved
AOT are given for the forest fires in Portugal around the 10 th July 2005.
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