A vegetation index — 0 compatible sensors — Last revised June 1, 2025
NDWI

Normalized Difference Water Index (Gao)

Vegetation water content index for remote sensing of vegetation liquid water. Sensitive to changes in leaf water content and useful for drought stress assessment.

Used in crop monitoring, forest monitoring, water detection, and fire & burn mapping.

When to use

  • Time-series monitoring of crop health, growth stages, and stress detection
  • Land cover classification and vegetation type discrimination
  • Biomass estimation and net primary productivity studies
  • Drought impact assessment over agricultural and forest areas
  • Phenology tracking — green-up, peak season, and senescence
  • Vegetation Water Content
  • Drought Stress Assessment

Limitations

  • Saturates in dense canopies (LAI > 3) — values plateau and lose discrimination ability
  • Sensitive to atmospheric scattering, especially blue-band haze
  • Soil background contaminates measurements in sparsely vegetated areas
  • Sun-sensor geometry (BRDF effects) introduces variability across acquisitions
  • Cloud cover and shadows produce invalid pixels that need masking

What the values mean

-1 Water / Snow
-0.1 Bare ground / Built-up
0.1 Sparse / Stressed
0.3 Moderate vegetation
0.5 Healthy vegetation
0.7 Dense canopy
Surface typeTypical NDWI
Open water, snow-0.3 to -0.1
Bare soil, urban-0.1 to 0.2
Sparse or stressed crops0.2 to 0.4
Healthy crops, grassland0.4 to 0.7
Dense forest, peak season0.7 to 0.9

General Formula

NIR 860 nm
SWIR 1240 nm

Sensor-Specific Formulas

Most-used sensors — click to show code below

SensorProviderFormulaBand Mapping

Code Examples

ndwi_gao_generic.py

NDWI vs other vegetation indices

IndexNameHow it differs
ARIAnthocyanin Reflectance IndexAlternative vegetation index — different band combination
mARIModified Anthocyanin Reflectance IndexRefined formulation for specific conditions
ARVIAtmospherically Resistant Vegetation IndexAtmospherically corrected version
ARVI2Atmospherically Resistant Vegetation Index 2Atmospherically corrected version

Related Vegetation Indices

ARI
Anthocyanin Reflectance Index
mARI
Modified Anthocyanin Reflectance Index
ARVI
Atmospherically Resistant Vegetation Index
ARVI2
Atmospherically Resistant Vegetation Index 2
BGI
Blue Green Pigment Index
BNDVI
Blue Normalized Difference Vegetation Index
bNIRv
Blue Near-Infrared Reflectance of Vegetation
BRI
Blue Red Pigment Index

References

Gao (1996)

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