Thursday, 13 January 2005
Deriving a Global Surface Albedo Map from Geostationary Observations
Monitoring and understanding climate changes of the Earth require the generation of long-term and consistent global data set from observation. In this context, geostationary satellite observations could play a significant role thanks to the long duration of the missions and the corresponding archives, often covering more than two decades. In particular, their frequent cycle of acquisition can be used to document the anisotropy of the surface and therefore surface albedo. Recently, Pinty et al. proposed a new method to characterise simultaneously surface anisotropy and atmospheric scattering properties, explicitly accounting for the radiative coupling between these two systems. The approach relies on a daily accumulation of geostationary observations acquired at different illumination conditions to document the angular effects. This method has already been successfully applied to derive systematically surface albedo from Meteosat-5 and –7 spacecraft, located respectively over the 63 degrees East and 0 degree positions. Such algorithm is currently being applied for the processing of GOES and GMS data. The processing of these observations for the generation of a consistent albedo product raises however challenging problems related to different spectral, temporal or spatial resolution. The analysis of the overlap areas between two adjacent spacecraft offers a unique opportunity to evaluate the consistency among products. An analysis of the Meteosat-5 and –7 overlapping area shows that these products agree within a relative error of about 6%, demonstrating thereby the robustness of the proposed approach to account for surface anisotropy. Similar analyses are ongoing for GOES and GMS-derived surface albedo. Hence, geostationary satellite observations acquired at a high temporal resolution of one hour or less open new avenues to document scattering processes in the aerosol-loaded atmosphere and at the surface. Although these observations are limited to one single large VIS band, the daily angular sampling permits to derive consistent albedo maps.