EVI - Enhanced Vegetation Index

EVI is similar to Normalized Difference Vegetation Index (NDVI) and can be used to quantify vegetation greenness. However, EVI corrects for some atmospheric conditions and canopy background noise and is more sensitive in areas with dense vegetation.

In areas of dense canopy cover, where leaf area index (LAI) is high, the blue wavelengths can be used to improve the accuracy of NDVI, as it corrects for soil background signals and atmospheric influences.

The Landsat 8 Surface Reflectance (SR) image on the left and the SR-derived Enhanced Vegetation Index (EVI) on the right are shown in this image.

The Landsat 4-5 Thematic Mapper (TM), Landsat 7 Enhanced Thematic Mapper Plus (ETM+), and Landsat 8-9* Operational Land Imager (OLI)/Thermal Infrared Sensor (TIRS) Collection 1 and Collection 2 scenes are processed to Landsat Level-2 Surface Reflectance products, from which the Landsat Surface Reflectance-derived Enhanced Vegetation Index (EVI) is derived.

EVI is a tool for measuring vegetation greenness that is similar to the Normalized Difference Vegetation Index (NDVI). EVI, on the other hand, compensates for some atmospheric factors and background noise from the canopy and is more sensitive in regions with dense vegetation. It incorporates a "L" value to account for the canopy background, "C" values as atmospheric resistance coefficients, and values from the blue band (B).  These enhancements allow for index calculation as a ratio between the R and NIR values, while reducing the background noise, atmospheric noise, and saturation in most cases.

EVI = G * ((NIR - R) / (NIR + C1 * R – C2 * B + L))

Generic Formula (R is the reflectance at the wavelengths (nm) denoted by the subscripts): 

Formula by Sentinel-2 bands: 

Values description: The range of values for EVI is -1 to 1, with healthy vegetation generally around 0.20 to 0.80.

References:

• Yang, Y., Fang, J., Tang, Y., Ji, C., Zheng, C., He, J., & Zhu, B. (2008). Storage, patterns and controls of soil organic carbon in the Tibetan grasslands. Global change biology, 14(7), 1592-1599.