The normalized difference vegetation index (NDVI) is a simple graphical indicator that can be used to assess whether the target being observed contains live green vegetation or not.
In an effort to monitor major fluctuations in vegetation and understand how they affect the environment, 35 years ago Earth scientists began using satellite remote sensors to measure and map the density of green vegetation over the Earth.
By carefully measuring the wavelengths and intensity of visible and near-infrared light reflected by the land surface back up into space, scientists use an algorithm called a "Vegetation Index" to quantify the concentrations of green leaf vegetation around the globe.
When sunlight strikes objects, certain wavelengths of visible and near-infraredare absorbed and other wavelengths are reflected. 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.
Scientists create detailed maps of the Earth’s green vegetation density that identify where plants are thriving and where they are under stress (i.e., due to lack of water).