Normalized difference vegetation index (NDVI)

NDVI is an index that measures the presence and health of live vegetation in a satellite or aerial image, based on the fact that healthy plants strongly reflect near-infrared light while absorbing most visible red light for photosynthesis.

It is calculated as NDVI = (NIR - Red) / (NIR + Red), using the near-infrared and red reflectance bands from a remote sensing instrument. The result ranges from -1 to 1: values near zero or negative indicate bare soil, water or built-up surfaces, low positive values indicate sparse or stressed vegetation, and values approaching 1 indicate dense, healthy vegetation. This differs from simply viewing a true-color satellite image, since NDVI isolates the vegetation signal that the human eye and ordinary photos cannot separate from soil or shadow.

NDVI is a staple of satellite imagery analysis in agriculture, where it supports crop-health monitoring and yield forecasting, and in environmental work tracking drought, deforestation and land-cover change over time. Analysts typically load NDVI time series into a geographic information system for field- or region-level spatial analysis. A common pitfall is comparing NDVI values across different sensors or seasons without correcting for atmospheric conditions and sun angle, both of which shift the index independent of any real change in vegetation.