MSG Improved Capabilities for Marine Aerosol Characterization

Despite their significant contribution to the Earth radiative budget, aerosol spatial and temporal distributions are still insufficiently quantified at the global scale because of the variability of aerosol sources, particle size distributions and chemical compositions. Satellite observations are well suited to provide the climate community with the needed aerosol load distributions, even if most aerosol products suffer from a poor daily coverage. Compared to existing orbiting sensors such as MODIS or POLDER or to less sophisticated geostationary sensors such as METEOSAT or GOES, MSG multi-spectral measurements in the visible and near-infrared offer new opportunities to study aerosols at high temporal and spatial resolutions over oceans. The MSG field-of-view is particularly suitable for the monitoring of aerosol load and transport over the Atlantic and the Mediterranean, in particular Saharan dust from North Africa, biomass-burning aerosols from subtropical Africa and pollution plumes from Europe. We developed an inversion technique that relies on MSG bands at 0.6 and 0.8 µm to estimate both aerosol optical thickness and Angström coefficient, a parameter characteristic of the particle size distribution. Spectral MSG measurements are compared to pre-computed values to find the best match. These theoretical values were computed using the 6S radiative transfer model (Vermote et al., 1997) for a set of aerosol models, which have been extrapolated from the Shettle and Fenn (1979) models to cover Angström coefficient values between 0 and 2.5. This inversion technique was applied to nine images per day between 09:00 and 16:00 UT for June 2003. A comparison with AERONET in-situ measurements performed in the tropical Atlantic and in the Mediterranean shows that MSG retrievals have a good accuracy in terms of both optical thickness and Angström coefficient. Monthly mean maps of both parameters are compared to that of the POLDER sensor for the same period, showing the benefit of using several images per day instead of one single orbit.