Near real-time provision of downwelling shortwave radiation estimates derived from satellite observations

The EUMETSAT Satellite Application Facility for Land Surface Analysis operationally delivers estimates of the downwelling Shortwave radiation flux, which constitutes an important variable for characterising the surface energy budget. The product is derived from observations provided by the SEVIRI instrument onboard the geostationary satellites of the Meteosat Second Generation series. The spatial coverage of the product includes Europe, Africa, the Middle East, and parts of South America. It is generated every 30 min and distributed to the users in near real-time. For clear sky conditions the flux estimate is determined with a parameterisation of the atmospheric transmittance as a function of the concentration of atmospheric constituents. For overcast sky a simple physical model of the radiation transfer in the cloud-atmosphere-surface system is employed, for which the satellite signal supplies the essential input information. The product has been validated with in situ data from six European ground measurement stations. The resulting statistics show a standard deviation of the difference between instantaneous satellite estimates and ground measurements in the order of 40 W m(-2) for clear sky data and I 10 W m(-2) for cloudy sky data. For the complete sample including all data points the standard deviation amounts to 85 W m(-2). The bias between the satellite product and the ground data is small with absolute values of less than 10 W m(-2). Copyright (c) 2008 Royal Meteorological Society.