NDVI - Vegetation Index
The Normalized Difference Vegetation Index (NDVI) constitutes a good measurement of the physiological activity of the plants; also, in empirical studies, it shows a correlation of between 85 and 90% with the crops yields.
The NDVI is an index calculated based on the radiation of remote sensing reflection bands:
//insert image of NDVI Formula
1 and 2 are the reflectance of the infrared and red bands; in the particular case of Landsat images, it corresponds to bands 4 and 3.
These bands are selected because of the spectral response of the vegetation, which has a high reflectance to the near-infrared band, while the red band is used as a reference, since it always keeps a near constant value.
Spectral behavior of the ground elements
Analysis of the spectral response of healthy vegetation
This index varies between known parameters (-1, 1). This facilitates its clasification since values less than 0.2 the foliar activity is low, while values greater than 0.4 correspond to active levels of foliar activity.
It has a direct relation with the quantity, quality and development of vegentation, and it correlates well with the yield of a given field in key dates.