What is NDVI? Vegetation Indices Explained

What is NDVI?

NDVI (Normalized Difference Vegetation Index) is a vigour indicator computed from how a plant responds to near-infrared (NIR) and red light:

NDVI = (NIR − Red) / (NIR + Red)

Healthy leaves absorb red light for photosynthesis and strongly reflect NIR. So NDVI is high over healthy vegetation (0.6–0.9), low over soil (0.1–0.2) and negative over water.

Other Indices

• NDRE: uses the red-edge band instead of red. Shows differences better in dense canopy where NDVI saturates.
• GNDVI, GCI: use the green band; more sensitive to chlorophyll content.
• VARI, ExG, GLI, TGI: computed from RGB bands only; an approximation for cameras without an NIR band.

Things to Watch

• True NDVI cannot be computed from an RGB camera; a multispectral camera is needed.
• Comparing NDVI across days requires radiometric calibration.
• Cloud shadows and low sun angles push the value artificially low.

For flight planning and calibration advice, see Plant Health with Multispectral Drones.