NDVI

NDVI (Normalized Difference Vegetation Index) values are a measure for the presence and condition of green vegetation.

NDVI values are calculated from two satellite bands; one band containing visible or red reflectance values, the other band near-infrared reflectance values. Use the NDVI function in MapCalc: NDVI(a,b) in which a is the band with visible or red reflectance and b the band with near-infrared reflectance.

The NDVI is calculated as:

near infrared band - visible band

near infrared band + visible band

NDVI values range from -1 to 1:

• Vegetated areas will generally yield high values because of their relatively high near-infrared reflectance and low visible reflectance.
• In contrast, water, clouds, and snow have larger visible reflectance than near-infrared reflectance. Thus, these features yield negative index values.
• Rock and bare soil areas have similar reflectances in the two bands and result in vegetation indices near zero.