NDVI
Also called: Normalized Difference Vegetation Index
NDVI (Normalized Difference Vegetation Index) is a satellite- or drone-derived measurement of crop vigor calculated as (NIR − Red) / (NIR + Red). Values range from -1 to +1, with healthy vegetation typically between 0.4 and 0.9. NDVI is the most widely used remote-sensing index in agriculture because it correlates strongly with biomass, chlorophyll content, and yield potential.
How NDVI Works
NDVI exploits a physical property of healthy plants: chlorophyll absorbs most red light for photosynthesis and reflects most near-infrared (NIR) light. The greater the contrast between NIR and Red reflectance in a pixel, the healthier the vegetation. Bare soil typically has NDVI between 0.1 and 0.2, stressed crops 0.2 to 0.4, and vigorous crops 0.5 to 0.9.
In precision agriculture, NDVI is used for three main workflows: (1) weekly in-season crop monitoring to spot stress zones before the eye can see them, (2) variable rate application (VRA) of nitrogen — zones with low NDVI get more fertilizer — and (3) yield-potential mapping at the end of the season. Free NDVI imagery is available from Sentinel-2 (10 m resolution, 5-day revisit) and Landsat (30 m, 16-day revisit); commercial platforms offer sub-meter drone-derived NDVI.
NDVI has known limitations: it saturates at high biomass (values above ~0.8 are hard to differentiate), it cannot distinguish between nitrogen stress and water stress, and cloud cover can make satellite imagery unusable for days. Advanced indices like NDRE, EVI, and SAVI address some of these limits. WiseYield monitors per-field Sentinel-2 NDVI for fields with a drawn boundary (Harvest and above) and flags a field whose canopy declines against its own recent passes — a field-level trend with its cloud-free share shown, not zone maps.
Sources
- Rouse et al. (1974). Monitoring vegetation systems in the Great Plains with ERTS. NASA.
- Sentinel-2 User Handbook, European Space Agency (2023).