NDVI

NDVI has been shown to be correlated with green leaf biomass and green leaf area index. Chlorophylls, the primary photosynthetic pigments in green plants absorb light primarily from the red and blue portions of the spectrum, while a higher proportion of infrared is reflected or scattered. NDVI tends to increase with increases in green leaf biomass or leaf area index. Rock and bare soil have similar reflectance in the red and the near infrared, so these surfaces will have values near zero.

NDVI is calculated using the following formula:

Near-infrared - red
Near-infrared + red

NDVI has been found to be useful for continental or global scale vegetation monitoring because it can compensate for changing illumination conditions, surface slope, and viewing aspect. NDVI can be used to detect seasonal changes in green biomass, but can also be used to detect changes to human activities (logging) or natural disturbances such as wild fire.

The data shown here are derived from Advanced Very High Resolution Radiometer (AVHRR) data from 1990 and 1992. The NDVI values are the maximum for each biweekly time period. Pixels cover approximately 1 Km in area.