NDVI — Normalized Difference Vegetation Index
NDVI (Normalized Difference Vegetation Index) is a numeric measure of vegetation health calculated from the red and near-infrared bands of a multispectral image. Healthy chlorophyll-rich plant tissue reflects strongly in the near-infrared and absorbs red light. The ratio yields a per-pixel score between -1 and +1 — higher values indicate denser, healthier vegetation.
Formula
NDVI = (NIR - RED) / (NIR + RED)
where NIR is the near-infrared reflectance value and RED is the red-band reflectance value for the same pixel.
Interpretation ranges
- -1.0 to 0.0 — water, bare soil, snow, asphalt; no vegetation signal
- 0.0 to 0.2 — bare ground, fallow, very early emergence
- 0.2 to 0.4 — sparse or stressed vegetation
- 0.4 to 0.7 — moderately dense, healthy crop canopy
- 0.7 to 1.0 — dense canopy at peak vigour
Why drone NDVI matters in Alberta agriculture
Field-scale NDVI from satellites (Sentinel-2, Landsat) has been available for years but resolves at 10-30 m per pixel — fine for regional trend mapping, poor for in-field decisions. A drone-mounted multispectral camera resolves NDVI at 3-5 cm per pixel, enough to identify a single underperforming wheel-track or a localized fungal infection inside a quarter section.
Common Alberta applications:
- Canola scouting for early sclerotinia or aster yellows pressure
- Wheat and barley nitrogen variability mapping (variable-rate fertilizer prescriptions)
- Pasture biomass and grazing rotation planning
- Hail, drought, frost and herbicide damage assessment for crop insurance claims
- OFCAF-supported variable-rate input verification
Sensors
Common drone-mounted NDVI-capable cameras:
- MicaSense RedEdge / Altum (5+ discrete bands plus thermal)
- Sentera 6X Multispectral
- DJI Phantom 4 Multispectral (legacy)
- Parrot Sequoia (legacy)
NDVI itself requires only red and NIR bands; multi-band sensors capture additional indices (NDRE, GNDVI, MCARI) for nuanced agronomic interpretation.
NDVI vs NDRE
NDRE substitutes the red-edge band (around 720 nm) for the visible-red band. Red-edge light penetrates deeper into the canopy, so NDRE is more sensitive once a crop has closed canopy and NDVI has saturated. Late-season Alberta wheat or canola is often better assessed with NDRE; early-season NDVI is the standard.