The wine industry has been using aerial imaging to measure vine vigor for decades. It is becoming more and more common for vineyard managers to use vigor maps to support their decision making in the field. These maps most often use the Normalized Difference Vegetation Index (NDVI) to measure vine vigor. NDVI has been the standard in the wine industry since the Mondavi Project in 1992.
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. Less vigorous or sparse vines reflecting both more visible and near-infrared light.
What many do not know, is that NDVI was not designed to measure plant vigor. It was designed to simply detect living vegetation and distinguish it from other matter like rocks, soil, or dead vegetation. With that in mind, it isn’t hard to understand why as an index for measuring vine vigor, NDVI is loaded with potential errors and inaccuracies.
Inherent shortcomings of NDVI
One of the most important shortcomings of NDVI is its dependency on the time of day at which the aerial images are taken. Since NDVI does not correct for changes in solar incidence angle (the angle at which the sun shines on the leaves) NDVI produces vastly different results throughout the day. Even though the vigor and health of the vines has obviously not changed in just a couple of hours. NDVI produces inaccurate data due to varying factors including shadowing, air moisture, and variations in the soil.
As you can see in the images above, NDVI produces vastly different results when taken at different times on the same day. Clearly the vigor of the vines has not changed over a 3-hour period, as would be implied from the images above.
Using advanced algorithms and additional wavelengths of light, VineView is able to eliminate these errors, and correct for the inaccuracies of NDVI with the Enhanced Vegetation Index (EVI).
EVI: Enhanced Vegetation Index
The Enhanced Vegetation Index (EVI) is calculated similarly to NDVI but uses additional wavelengths of light to correct for the inaccuracies of NDVI. Variations in solar incidence angle, atmospheric conditions like distortions in the reflected light caused by the particles in the air, and signals from the ground cover below the vegetation are corrected for using EVI.
See how the EVI results stay consistent over a 3-hour period. Using additional spectral information and calculations, EVI corrects for the difference in atmospheric conditions and solar incidence angle, providing you with more accurate, actionable data.
VineView also uses both multi and hyperspectral data which allows us to spectrally isolate the grapevine from the surrounding soil and cover crop, so you get just the vine canopy information, and none of the “noise”.
Another benefit of EVI is that is allows grape growers to accurately compare data and track changes in vine vigor over time. Using our vigor products scaled to an absolute standard makes these comparisons quick and easy!