Comparative Vegetation Index East and West of the Andes26.6S 68.9W
The Normalized Difference Vegetation Index (NDVI) is a simple graphical indicator that can be used to analyze satellite data, and assess whether the target being observed contains live green vegetation or not.
Live green plants absorb solar radiation in the photosynthetically active radiation (PAR) spectral region, which they use as a source of energy in the process of photosynthesis. Leaf cells have also evolved to scatter (i.e., reflect and transmit) solar radiation in the near-infrared spectral region. Hence, live green plants appear relatively dark in the PAR and relatively bright in the near-infrared.
The pigment in plant leaves, chlorophyll, strongly absorbs visible light (from 0.4 to 0.7 µm) for use in photosynthesis. The cell structure of the leaves, on the other hand, strongly reflects near-infrared light (from 0.7 to 1.1 µm). The more leaves a plant has, the more these wavelengths of light are affected, respectively.
Since early instruments of Earth Observation acquired data in visible and near-infrared, it was natural to exploit the strong differences in plant reflectance to determine their spatial distribution in these satellite images. Here, the color contrast shows a stark difference in the vegetation index between arid Chile and western Bolivia, which appear brown to yellow (low vegetation index), and more fertile Argentina, which appears green (high vegetation index).