The fraction of absorbed photosynthetically active radiation (FAPAR, sometimes also noted fAPAR or fPAR) is the fraction of the incoming solar radiation in the
photosynthetically active radiation Photosynthetically active radiation (PAR) designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis. This spectral region corresponds more o ...
spectral region that is absorbed by a
photosynthetic organism
In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...
, typically describing the light absorption across an integrated plant canopy.
This biophysical variable is directly related to the primary productivity of photosynthesis and some models use it to estimate the assimilation of carbon dioxide in vegetation in conjunction with the
leaf area index. FAPAR can also be used as an indicator of the state and evolution of the vegetation cover; with this function, it advantageously replaces the
Normalized Difference Vegetation Index
The normalized difference vegetation index (NDVI) is a simple graphical indicator that can be used to analyze remote sensing measurements, often from a space platform, assessing whether or not the target being observed contains live green veget ...
(NDVI), provided it is itself properly estimated.
FAPAR can be directly measured on the ground, by putting a spectrometer above and below canopy cover. On a larger scale, however, it is estimated from space measurements in the solar spectral range and a number of state of the art
algorithm
In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific problems or to perform a computation. Algorithms are used as specifications for performing ...
s have been proposed to derive this important environmental variable.
Currently, there are some remote sensing products of FAPAR, such as AVHRR and MODIS.
FAPAR is one of the 50
Essential Climate Variables
The Global Climate Observing System (GCOS) was established in 1992 as an outcome of the Second World Climate Conference, to ensure that the observations and information needed to address climate-related issues are obtained and made available to ...
recognized by the UN
Global Climate Observing System
The Global Climate Observing System (GCOS) was established in 1992 as an outcome of the Second World Climate Conference, to ensure that the observations and information needed to address climate-related issues are obtained and made available to ...
(GCOS) as necessary to characterize the climate of the Earth. GCOS has issued specific recommendations to monitor this variable systematically, both through a reanalysis of existing databases and in the future with current and forthcoming instruments.
References
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External links
Information on and distribution of FAPAR productsGCOS Implementation PlanMODIS FPAR websiteEarth Snapshot FAPAR images
Photosynthesis