The black sky and white sky albedo products represent the fraction of radiation
reflected by the surface under two extreme conditions. Black sky albedo represents the
fraction of reflection when incoming light is in a direct beam whereas white sky albedo
represents the fraction of reflection when the light source is isotropic diffuse. The albedo
under realistic incoming solar radiation can be approximated as the combination of these
two as a function of the fraction of direct and diffuse radiation (31, 32). Here we
extracted the MODIS BRDF parameters to calculate the black sky albedo every 3 hours
with the MODIS RossThickLiSparse BRDF model, since the MODIS black sky albedo
was operationally produced only at local solar noon. The actual albedo was then derived
as a sum of black sky albedo and white sky albedo weighted by the fraction of direct and
diffuse surface incoming shortwave radiation. We used the monthly 3-hourly direct and
S8
diffuse shortwave radiation data derived with the shortwave algorithm of the NASA
World Climate Research Programme /Global Energy and Water-Cycle Experiment
(WCRP/GEWEX) Surface Radiation Budget (SRB) Project (33). The radiation data were
obtained from the Langley Atmospheric Sciences Data Center
(http://eosweb.larc.nasa.gov/PRODOCS/srb/table_srb.html).