MNDWI
Modified Normalized Difference Water Index. An enhancement of NDWI that uses the shortwave infrared (SWIR) band instead of NIR, providing better discrimination between water bodies and built-up areas in urban environments.
Formula
MNDWI = (Green - SWIR) / (Green + SWIR)Overview
The Modified Normalized Difference Water Index (MNDWI) extracts open water features from satellite imagery while suppressing noise from built-up land. Developed by Hanqiu Xu in 2006 as an improvement over McFeeters' NDWI, it substitutes SWIR for NIR, exploiting water's stronger SWIR absorption and built-up surfaces' higher SWIR reflectance.
How It Works
MNDWI = (Green − SWIR) / (Green + SWIR). On Sentinel-2: (B3 − B11) / (B3 + B11). Water produces strongly positive values because it absorbs SWIR. Built-up areas produce negative values due to high SWIR reflectance. A threshold around 0.0–0.3 separates water from non-water.
Key Facts
- Formula: (Green − SWIR) / (Green + SWIR)
- Key advantage over NDWI: suppresses built-up area false positives.
- Sentinel-2 bands: B3 (Green) and B11 (SWIR-1, 20 m resolution).
Applications
Urban Water Body Mapping
Excels at detecting water bodies within cities where NDWI misclassifies buildings as water.
Flood Extent Monitoring
Delineating inundated areas in mixed urban-rural floodplains.
Coastal Monitoring
Tracking shoreline changes and tidal flat exposure.
Limitations & Considerations
Can struggle with turbid water. Shadows from tall buildings may mimic water. The SWIR band on Sentinel-2 (20 m) limits spatial detail compared to the green band (10 m).
History & Background
Published by Hanqiu Xu in 2006 in the International Journal of Remote Sensing as a direct improvement to McFeeters' 1996 NDWI. Now the standard choice for urban water mapping.
Analyze MNDWI data with LYRASENSE
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