Fraction of Absorbed Photosynthetically Active Radiation (FAPAR)

The fraction of radiation absorbed by photosynthetically active vegetation (FAPAR) defines the fraction of photosynthetically active radiation (400-700 nm) absorbed by the green leaves of the forest canopy and, therefore, translates the green vegetation capacity to absorb energy. FAPAR depends on the structure of the canopy and leaves, as well as the optical properties of the soil and irradiance conditions.

The FAPAR product is considered one of the fundamental variables for studying the terrestrial system in the context of global change. It is an essential variable in models that evaluate the primary productivity of vegetation and in carbon cycle models that implement the most recent schemes for characterizing the processes of terrestrial surfaces. In addition, the FAPAR product is an indicator of vegetation health and has a good correlation with the leaf area index (LAI), especially for healthy and fully developed canopies.

The FAPAR product has the spatial resolution of the MSG / SEVIRI instrument and is generated daily based on an iterative scheme with a time window of five days. The FAPAR product is expressed in the range of 0% to 100%, with no values in the pixels covered by clouds. The uncertainty derived from variations in the viewing / sun angles and the anisotropic effects of surface reflectance is corrected by using the same geometry for the entire SEVIRI disk. The FAPAR product includes routine quality checks and error estimates.