Land Surface Albedo Derived on a Daily Basis From Meteosat Second Generation Observations

Land surface albedo determines the repartition of downwelling solar radiation into components that are either reflected back to the atmosphere or absorbed by the surface. As more sophisticated soil-vegetation-atmosphere transfer schemes are being implemented in numerical meteorological models, it will become increasingly important to accurately characterize the spatial and temporal albedo variations. Within the scope of the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Satellite Application Facility for Land Surface Analysis, we have developed a daily albedo product, which is derived in near real time from observations provided by the Spinning Enhanced Visible and Infrared Imager (SEVIRI) instrument onboard the geostationary satellites of the Meteosat Second Generation series. The basic algorithm concept comprises an atmospheric correction scheme, the inversion of a linear semi-empirical model of the bidirectional reflectance distribution function, the angular integration of the bidirectional reflectance distribution function to obtain spectral albedo, and the application of suitable conversion relations to derive broadband albedo estimates. The reflectance model inversion is performed each day based on the available set of clear-sky observations. In addition, constraints on the model parameters are taken into account in the inversion process. By specifying these constraints according to the previous model output in a recursive manner, a complete spatial coverage of the resulting albedo maps is achieved while, at the same time, preserving a high temporal resolution. This paper primarily concentrates on the description of the methodology. In addition, examples for the obtained albedo maps and time series, as well as the first validation results, are presented.