The use of aerial imaging to measure vine vigor is nothing new in the wine industry. In fact, most vineyard owners and managers currently utilize some form of vigor mapping in their vineyards to aid their decision making. Long considered the industry standard, the most common measure of vine vigor has been the Normalized Difference Vegetation Index, or NDVI.
What many do not know, however, is that NDVI was not originally designed to measure plant vigor. Instead, it was designed simply to detect living vegetation and distinguish it from other matter, like rocks, soil, or dead vegetation. It was not until the Mondavi Project of 1992 that scientists began to correlate NDVI imaging with vine vigor.
As an index, NDVI is fraught with potential errors and inaccuracies. One of the main factors which affects the results of NDVI analysis is the solar incidence angle, or simply put, the angle at which the sun strikes the leaves. Since the earth is constantly rotating, and in motion around the sun, the solar incidence angle is continuously changing. Therefore, there is no way to ensure that the data you receive is accurate. There is no way to set the data relative to a standard, since the results change dramatically during a single day (Photos 1 & 2).
NDVI images captured at different times on the same day (11am and 2pm) show dramatically different results:
Shadows and soil variations also have a large impact on NDVI results, which can skew the data away from an accurate representation of actual vine conditions (Photo 3).
Using new algorithms and additional wavelengths of light, scientists at VineView Imaging are able to eliminate these errors and inaccuracies (Photos 4 & 5). We provide an improved Enhanced Vegetation Index, or EVI, that allows vineyard owners and managers to accurately compare data and track change in vine vigor over time.
EVI images captured at different times on the same day (11am and 2pm) provide consistent results:
Additionally, the use of both multi- and hyperspectral data allows VineView to spectrally isolate the grapevine canopy from the surrounding soil and cover crop. We call this our PureCanopy™ EVI, because it measures the vigor of the canopy, and nothing else (Photo 6).
Aerial imaging is an important tool that, when analyzed and acted upon appropriately, can dramatically improve the quality of the grapes produced in your vineyard.
VineView has been providing EVI imaging for more than half a decade. The content of this post is from VineView and does not represent the opinions of the Lodi Winegrape Commission.
If you are currently using NDVI imaging to analyze vine vigor in your field and want to learn more about EVI vigor mapping, you can contact VineView for additional information. Visit their website, www.vineview.com, or contact them directly at (707) 965-9663 or firstname.lastname@example.org.
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