Absorbed Photosynthetically Active Radiation APAR

APAR is the fraction of the PAR (Photosynthetically Active Radiation) absorbed by the canopy and used for carbon dioxide assimilation. PAR refers to the visible part of the solar spectrum between 0.4 and 0.7 ^m, where chlorophyll absorbs solar radiation. APAR is a key parameter in productivity analysis and ecosystem modeling. The productivity of vegetation canopies can be studied from estimation of APAR derived from optical remote sensing data.

The APAR results from a leaf radiation balance : APAR = PAR - ppAR . PAR - PAR^ + PARsoU

where, ppar is the canopy reflectance at the upper side of the canopy in the 0.4 to 0.7^m spectral range, PARtrans is the amount of PAR that is transmitted through the canopy and directed to the soil; PARsoil that is reflected from the soil underneath the canopy and is received back at the lower side of the canopy.

APAR can be deduced directly from PAR after simplifying the previous equation into :

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