MODIS Directional Surface Reflectance Product: Method, Error Estimates and Validation

The surface bidirectional reflectance factor (BRF) is the ratio between reflected radiance measured in specific observation geometry (zenith and azimuth) within an infinitely small solid angle and irradiance incident on the surface from a direct source of illumination (zenith and azimuth). The BRF is determined from satellite observations through an atmospheric correction (AC) process. When properly retrieved, the surface BRF is fully decoupled from an atmospheric signal, and thus represents the value as measured by an ideal sensor held at the same view geometry and located just above the Earth’s surface assuming an absence of atmosphere.