Normalized difference water index (NDWI)

"Known to be strongly related to the plant water content. It is therefore a very good proxy for plant water stress. It is a satellite-derived index from the Near-Infrared (NIR) and Short Wave Infrared (SWIR) channels. The SWIR reflectance reflects changes in both the vegetation water content and the spongy mesophyll structure in vegetation canopies, while the NIR reflectance is affected by leaf internal structure and leaf dry matter content but not by water content. " (European Commission, 2011)

Sources

European Commission. NDWI: Normalized Difference Water Index. 2011. Version 1. DESERT Action - LMNH Unit. Accessed March 13, 2019. Available at: http://edo.jrc.ec.europa.eu/documents/factsheets/factsheet_ndwi.pdf