This data comprises the distribution of the surface solar irradiance (in W/m²) as obtained from observations of the geostationary first generation Meteosat satellites no. 2-7 (MVIRI) (compare EUMETSAT albedo).
This EUMETSAT CM-SAF data product is based on a combination of the Heliosat approach to obtain the effective cloud albedo from uncalibrated MVIRI radiances (Hammer et al., 2003, see References) with a radiative transfer model specifically designed for clear sky conditions (MAGIC, Mueller et al., 2009, see References). The Heliosat approach is merely based on MVIRI data while the radiative transfer model MAGIC and the final irradiance retrieval requires a number of additional parameters: atmospheric total water vapor content (ERA-Interim and ERA40), an ozone climatology, the surface albedo (SARB/CERES) and an aerosol climatology. More information is given in the user manual.
Targeted uncertainties (mean total bias < 10 W/m², 90% of all individual biases < 10 W/m²) are usually met everywhere except in regions with complex topography and snow cover. Here uncertainties in the local incidence angle as well as in the observed snow covered area lead to larger uncertainties in the retrieved irradiance. Over bright surfaces such as snow and sand deserts the retrieval of the effective cloud albedo has larger uncertainties because of the reduced contrast between the surface and clouds and therefore the obtained irradiance also can have larger uncertainties. More information about uncertainties / limitations is given in the user manual and in the validation report.