EVI vs NDVI: What’s the difference?
Inherent shortcomings of NDVI
For decades Normalized Difference Vegetation Index (NDVI) has been the wine industry’s standard for measuring vine vigour. NDVI is a calculation between the near-infrared light reflected by vegetation and the visible light. Healthy, more vigorous vines absorb more visible light and reflect more near-infrared light with less vigorous or sparse vines reflecting both more visible and near-infrared light.
NDVI often produces inaccurate data due to varying factors such as shadowing, atmospheric conditions, and variations in the soil. Another shortcoming of NDVI is its dependency on the time of day at which images are taken. Due to changes in solar incidence angle, NDVI produces vastly different results when images are taken just hours apart.
NDVI shows different results just three hours later even though the health of the vines has not changed. Image source: Vine View Scientific Aerial Imaging.
EVI: Enhanced Vegetation Index
Enhanced Vegetation Index (EVI) corrects for the inaccuracies of NDVI including variations in solar incidence angle, atmospheric conditions, and canopy background signals. EVI is calculated similarly to NDVI but uses additional wavelengths of light to correct for the distortions in the reflected light caused by the particles in the air as well as the ground cover below the vegetation.
While NDVI shows different results just two hours later, EVI is less sensitive to shadows and soil boundaries, providing consistent results every time. Image source: Vine View Scientific Aerial Imaging.