Where VIS and NIR stand for the spectral reflectance measurements acquired in the visible (red) and
near-infrared regions, these spectral reflectances are themselves ratios of the reflected over the incoming
radiation in each spectral band individually, hencethey take on values between 0.0 and 1.0. By design, the
NDVI itself thus varies between -1.0 and +1.0. It should be noted that NDVI is functionally, but not linearly,
equivalent to the simple infrared/red ratio (NIR/VIS) (Amini and Shataee, 2009). The advantage of NDVI over a
simple infrared/red ratio is therefore generally limited to any possible linearity of its functional relationship with
vegetation properties (e.g. biomass). In general, if there is much more reflected radiation in near-infrared
wavelengths than in visible wavelengths, then the vegetation in that pixel is likely to be dense and may contain
some type of forest. Subsequent work has shown that the NDVI is directly related to the photosynthetic
capacity and hence energy absorption of plant canopies.