Normalized Difference Water Index (NDWI)

Example map of median Normalized Difference Water Index (NDWI) (NIR/SWIR) in the central Rocky Mountains region, USA during June 23-July 22, 2023

Description

The normalized difference water index can be utilized for evaluating vegetation liquid water contents or water-inundated areas (Gao, 1996). NDWI is useful for evaluating reflectance from vegetation canopies that have similar scattering properties, but slightly different liquid water absorption due to canopy water content. As a result, NDWI is sensitive to changes in the liquid water content of vegetation canopies and open water areas. The common range of NDWI for green vegetation is -0.1 to 0.4 with 0.4 indicating high vegetation water content. 

Climate Engine provides a couple different versions of NDWI, utilizing normalized differences of different bands, which can be more useful for different applications: 

  • NDWI (NIR/SWIR1) = (NIR-SWIR1)/(NIR+SWIR1)
  • NDWI (GREEN/NIR) = (GREEN-NIR)/(GREEN+NIR)
  • NDWI (GREEN/SWIR1) = (GREEN-SWIR1)/(GREEN+SWIR1)
  • NDWI (GREEN/SWIR2) = (GREEN-SWIR2)/(GREEN+SWIR2)
  • NDWI (SWIR1/GREEN) = (SWIR1-GREEN)/(SWIR1+GREEN)

where NIR = near infra-red band, GREEN = green band, SWIR1 = 1.55 - 1.75 micrometer band, SWIR2 =2.08 - 2.35 micrometer band. 

References

Gao, B.C., 1996, NDWI - A normalized difference water index for remote sensing of vegetation liquid water from space. Remote Sensing of Environment, 58, 257–266.

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