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¿What is the EVI index?
The Enhanced Vegetation Index (EVI) is similar to the NDVI but optimized, as it includes corrections to reduce the influence of the atmosphere and the soil.
¿When is it used?
The EVI index is usually more reliable in two particular moments of the agricultural cycle:
- initial stages of the crop cycle, with little vegetation or weeds (low vegetation cover).
- late stages, with high density biomass (high greenness or NDVI saturation).
In addition, it is recommended to use this index if you are going to perform a time series analysis, involving several consecutive dates.
The EVI index maps are shown with the vegetation symbology:
- black and brown: indicate absence of vegetation.
- green: biomass development, emerging crops and weeds.
- blue and violet: high density of biomass.
The following images compare NDVI / EVI in a fallow field/farm, with presence of weeds (beginning of the cycle).
By incorporating atmospheric and brightness corrections, EVI reflects weed “spots” much better than NDVI.
These images compare NDVI / EVI in late stages of the crop cycle, where it is common for the NDVI to become saturated and more homogeneous, failing to express some differences, which are detected clearly by using the EVI.