NDVI

What is NDVI?

Most agriculture drones depend on multi-spectral imaging to spot problems with a crop’s health, specifically, they look at changes over time in Visible light (VIS) and Near-infrared (NIR) light reflected by crops.

It is possible to detect plant health from these images because plants reflect different amounts of visible green and NIR light, depending on how healthy they are. By measuring the changes in visible and NIR light reflected from a crop, we can spot potential health issues.

To monitor changes in plant health over time, drone images are processed to calculate a tracking index called NDVI (Normalized Difference Vegetation Index), which is a measure in the difference between light intensity reflected by the field in two different frequencies:

NDVI = (NIR-VIS)/(NIR+VIS)

NDVI is the most popular index calculated using drone data, but there are many others. Some of the more popular indices include:
  • CWSI (Crop Water Stress index): measures temperature differentials to detect / predict water stress in plants. Requires a thermal imaging sensor and the use of a nearby weather station.
  • CCCI (Canopy Chlorophyl Content Index): detects canopy nitrogen levels using three wavebands along the red edge of the visible spectrum. Requires visible and near infrared cameras.

NDVI

Leaf reflectivity [source: Agribotix]