NDVI is a vegetation health indicator.
It's the most widely used index in agriculture because it's easy to calculate, and most satellites can obtain the 2 bands needed for it.
- To characterize vegetation density.
- To check plant health.
- To evaluate different stages of plant development.
- To estimate field productivity.
NDVI is calculated using red and near-infrared (NIR) bands.
The photosynthesis process in healthy plants absorbs 90% of visible light and strongly reflects around 50%–60% of NIR. Unhealthy or sparse vegetation absorbs less visible light and reflects less near-infrared light.
NDVI ranges between –1 and 1. A value close to 1 means healthy vegetation.
The image below displays the NIR band as red. It's bright red in areas showing high reflectance from vegetation. The redder and the richer the area is, the more reflectance is going on from the vegetation.
- NDVI is quite sensitive to atmospheric effects. It doesn't apply any atmospheric correction, as EVI does.
- NDVI can be saturated when it presents a high level of leaf area index (LAI). To correct for LAI, use EVI.
- NDVI results are very sensitive to soil background effects during the early stages of crop growth when the green leaf area is small.
- When the development of a plant is accelerated, it is very difficult to distinguish the green of this plant from that of a plant with normal growth.