Because the spectral signature of vegetation is so characteristic, there are usually no problems in distinguishing between bare ground and green vegetation. As explained above, the difference between reflection in the visible and the near infrared ranges can be used to determine the extent of photosynthesis and plant growth. This can also be used to obtain information on the health status of the vegetation.

In the case of Landsat, channel4 is in the near infrared and channel3 in the red spectral range, so the equation for the NDVI is: (channel4 - channel3) / (channel4 + channel3)

How to read the animation: dark green indicates dense, healthy vegetation, beige areas bare soil. Note the seasonal north-south movement of the vegetation belt (also see the Background of the Weather and Climate section)

(Source of the animation: NASA/Goddard Space Flight Center Scientific Visualization Studio)