Surface albedo from space: Application over HAPEX-Sahel square degree

The importance of the influence of the surface albedo for energy budget is no longer to be demonstrated. Though, an accurate determination of this parameter is still uneasy to achieve over extensive areas, because the only available measurements at this scale being realised from space, they suffer of the directionnal behavior of the surface and of the temporal variability of the atmosphere. A method has been developped in order to achieve the computation of the albedo from satellite measurements and has been tested over bare soil (Cabot and Dedieu, 97). This method is based on a complete preprocessing of the data including atmospheric corrections, filtering for cloud and dust contamination and retrieval of the parameters of several models aimed at reproducing the bidirectional behavior of the surface. In this presentation, we show the application of the method to the Hapex Sahel data set (NOAA/AVHRR over the HAPEX square degree). Using the Rahman et al. (1993) model, we computed a map of parameters and used them to calculate hemispherical reflectance for the month of September 1992. Results of computation and comparison with on-ground measurements are presented, showing agreement up to 0.023 in rmse for sun at zenith.