The Normalized Difference Vegetation Index, a widely used spectral index that quantifies vegetation greenness and health from satellite imagery. NDVI is a proxy for plant biomass and is used to estimate crop water use and monitor drought impacts.
NDVI (Normalized Difference Vegetation Index) is calculated from the near-infrared (NIR) and red (RED) spectral bands of satellite imagery using the formula NDVI = (NIR - RED) / (NIR + RED). Healthy green vegetation strongly reflects NIR light and absorbs red light for photosynthesis, yielding high NDVI values (0.3-0.9), while bare soil, water, and stressed vegetation produce low values (-0.1 to 0.3). In hydrology and water resources, NDVI serves multiple purposes: estimating crop coefficients for irrigation water demand calculations, monitoring drought severity and agricultural impacts, assessing riparian vegetation health along waterways, and parameterizing evapotranspiration models. Time-series NDVI analysis reveals phenological patterns, growing season length, and long-term trends in vegetation productivity related to climate and water availability changes. NDVI can be computed from virtually any multispectral sensor including Landsat, MODIS, Sentinel-2, and commercial satellites. While NDVI is simple and robust, it saturates in dense canopies and is sensitive to soil background effects; enhanced indices like EVI (Enhanced Vegetation Index) address some of these limitations.