Surface Albedo

The surface albedo quantifies the fraction of the sunlight reflected by the surface of the Earth. Different albedo concepts are defined: 1) the directional albedo or directional-hemispherical reflectance (also called black-sky albedo) is the integration of the bi-directional reflectance over the viewing hemisphere. It assumes all energy is coming from a direct radiation from the sun, it is computed for a specific time; 2) the hemispherical albedo or bi-hemispherical reflectance (also called white-sky albedo) is the integration of the directional albedo over the illumination hemisphere. It assumes a complete diffuse illumination.

The Global Climate Observing System (GCOS) specified the black-sky albedo (directional albedo) as an Essential Climate Variable and the product is required for climate change purposes.