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GCOS Land ECV - Fraction of Absorbed Photosynthetically Active Radiation (FAPAR)

Solar radiation in the spectral range 400–700 nm, known as photosynthetically active radiation (PAR), provides the energy required by terrestrial vegetation to produce organic materials from mineral components. The part of this PAR that is effectively absorbed by plants is called FAPAR. It is a non-dimensional quantity varying from 0 (over deserts) to 1 (for large, deep, homogeneous canopy layers observed by medium- to low-resolution sensors), although the maximum value is never witnessed in practice because some of the incoming light is always reflected back by the canopy or the underlying ground. FAPAR is related to, but different from, LAI (covered in the following subsection), which describes the amount of leaf material in the canopy. FAPAR plays a critical role in assessing the primary productivity of canopies, the associated fixation of atmospheric CO2 and the energy balance of the surface. As is the case with land-surface albedo (section 6.3.9), FAPAR depends on the illumination conditions, that is, the angular position of the Sun with respect to the vegetation layer and the relative contributions of the direct and diffuse irradiances. Both black-sky (assuming only direct radiation) and white-sky (assuming that all the incoming radiation is in the form of isotropic diffuse radiation) FAPAR values may be considered.

Product Requirements:

  • Maps of FAPAR for Modelling:
    • Frequency:  Daily
    • Resolution:  200/500 m
    • Required Measurement uncertainty:  Max(10 %; 0.05)
    • Stability (per decade unless otherwise specified):  Max(3 %; 0.02)
    • Entity (Satellite):  WGClimate
  • Maps of FAPAR for Adaptation:
    • Resolution:  50 m
    • Required Measurement uncertainty:  max(10 %; 0.05)
    • Stability (per decade unless otherwise specified): max(3 %; 0.02)
    • Entity (Satellite):  WGClimate

Networks:

Data Sources: