Normalized Difference Vegetation Index
The Normalized Difference Vegetation Index (NDVI) is an indicator of the greenness of the biomes. As such, it is closely linked to the FAPAR.
Even though it is not a physical property of the vegetation cover, its very simple formulation
NDVI = (REF_nir – REF_red)/(REF_nir + REF_red)
where REF_nir and REF_red are the spectral reflectances measured in the near infrared and red wavebands respectively, makes it widely used for ecosystems monitoring.