Satellite-Derived Surface Radiation Budget over the African Continent. Part I: Estimation of Downward Solar Irradiance and Albedo

Abstract

Downward surface solar irradiance and albedo of the African continent are estimated from Meteosat B2 data at 30-km spatial resolution. The algorithm, based on Dedieu et al.?s approach, is verified against other satellite estimates and ground-based measurements. In the computations, the International Satellite Cloud Climatology Project?s (ISCCP) radiometric calibration is adjusted using the Libyan desert as a reference target of constant reflectance properties. Surface albedo is corrected for sun zenith angle effects, allowing for better detection of seasonal changes due to the vegetation cycle. The estimates obtained with Meteosat B2 data agree generally well with other satellite estimates, although biases of 20 W m?2 (downward surface solar irradiance) and 0.15 (surface albedo) are obtained in some cases. There is evidence, from comparisons with surface measurements, that the clear-sky downward surface solar irradiance is overestimated over semiarid regions of Africa because of uncertainties in aerosol characteristics. In the Sahel region, where spatial albedo gradients are high, it is advantageous to use 30-km Meteosat B2 products instead of the current, coarser 280-km-resolution ISCCP products.