¿What is the NDWI Index?

The Normalized Difference Water Index (NDWI) compares the difference between the green and near-infrared wavelengths.

NDWI = (Green – NIR)/(Green + NIR) [McFeeters, 1996]

¿What is it used for?

It is an appropriate index for mapping water bodies and flooded areas, since water has a high absorption and low irradiation in the visible range of infrared. For this index, the water bodies present values greater than 0, while the soil presents values less than 0. It is not an indicator of soil moisture, but it does allow determining the time of the cycle when waterlogging or flooding occurs.

Symbology.

The more water there is on the surface, the more the color palette tends to purple.

Examples.

The following image compares NDVI / NDWI. The marked sector, allows to observe low values of NDVI indicating the possibility of a bare soil. However, the NDWI shows us that there is a flooding in the area.