NDWI (McFeeters, open water)
The normalized difference water index of McFeeters 1996, from green and near-infrared reflectance: the one that maps open water.
Experimental: not yet fully verified. How results are checked
NDWI is 0.5.
Provenance
- Computed by
- raster.index.ndwi-mcfeeters 1.0.0, core 0.1.0
- Model
- NDWI = (Green - NIR) / (Green + NIR) on surface reflectance (McFeeters 1996)
- Accuracy
- Exact arithmetic on the reflectance given.
- Notes
- 1 shown with the answer
- Cites
- McFeeters, S. K., International Journal of Remote Sensing, The use of the Normalized Difference Water Index (NDWI) in the delineation of open water features
Something look off?
How we got thisFormula, worked example, sources, and proof
Model: NDWI = (Green - NIR) / (Green + NIR) on surface reflectance (McFeeters 1996)
Accuracy: Exact arithmetic on the reflectance given.
When to use this: Use this to pick open water out of an image: water reflects green and absorbs near-infrared, so lakes, rivers, and flooding stand out positive while land goes negative. It is the index to reach for when the question is where the water is.
Limitations: It confuses built-up surfaces with water, which is what MNDWI was proposed to fix, and it says nothing about water inside vegetation, which is Gao's index of the same name. A threshold of zero is a starting point rather than a rule: shadows, turbidity, and thin water over bright bottoms all move it.
Worked example: NDWI (McFeeters, open water). Source: McFeeters 1996: green 0.12 and NIR 0.04 give 0.5. It is golden test vector v003, and every build checks the tool still gives its answer within its tolerance.
You enter
- Green reflectance
- 0.12
- Near-infrared reflectance
- 0.04
You get
- NDWI
- 0.5
Review: Not yet independently reviewed by a GIS professional.
Last verified: 2026-09-22, when a maintainer last confirmed this tool's sources at the issuer. See the sources ledger.
Status: version 1.0.0, core 0.1.0. See this tool in the verification report.
Checked against: 10 golden test vectors (download the test vectors, each with its source and tolerance). See how results are checked and every source.
Sources
- The use of the Normalized Difference Water Index (NDWI) in the delineation of open water features, McFeeters, S. K., International Journal of Remote Sensing, Volume 17, issue 7, pages 1425-1432. NDWI = (Green - NIR) / (Green + NIR), for open water.
Terms
- NDWI: normalized difference water index
- Two different indices share this name: McFeeters 1996 uses green and near-infrared to map open water, and Gao 1996 uses near-infrared and shortwave-infrared to measure water inside vegetation. Source: The use of the Normalized Difference Water Index (NDWI) in the delineation of open water features
Experimental means this tool has not yet met the stable bar: at least 20 golden vectors, differential tests, and an independent worked example.