Normalised Difference Water Index (Gao, 1996)

The NDWI is sensitive to the change in the water content of leaves and it is computed using the near infrared (NIR - band 8A) and the short wave infrared (SWIR - band 11) reflectance. NDWI is also used to measure biomass and LAI (without saturation issues typical of e.g. NDVI), as the amount of canopy water is proportional to vegetation structure.

The index formula is defined as:
(B8a - B11) / (B8a - B11)