Normalized Difference Water Index (NDWI)
Index name: Normalized Difference Water Index (NDWI) and Land Surface Water Index (LSWI).
Ease of use: Green.
Origins: Developed from work done by Gao in the mid-1990s at the National Aeronautics and Space Administration (NASA) Goddard Space Center in the United States.
Characteristics: Very similar to the NDVI methodology, but uses the near-infrared channel to monitor the water content of the vegetation canopy. Changes in the vegetation canopy are used to identify periods of drought stress.
Input parameters: Satellite information in the various channels of the near-infrared spectrum.
Applications: Used for monitoring of drought affecting agriculture as a method of stress detection.
Strengths: High resolution and good spatial coverage over all terrains. Different to NDVI, as the two indices look at different signals.
Weaknesses: Stress to plant canopies can be caused by impacts other than drought, and it is difficult to discern them using only NDWI. The period of record for satellite data is short, with climatic studies being difficult.
Resources: The methodology is described in the literature as are the calculations based on the MODIS data being used, http://www.eomf.ou.edu/modis/visualization/.
Chandrasekar, K., M.V.R. Sesha Sai, P.S. Roy and R.S. Dwevedi, 2010: Land Surface Water index (LSWI) response to rainfall and NDVI using the MODIS vegetation index product. International Journal of Remote Sensing, 31:3987–4005.
Gao, B.C., 1996: NDWI—a Normalized Difference Water Index for remote sensing of vegetation liquid water from space. Remote Sensing of Environment, 58(3):257–266.
Note: The NDWI concept and calculations are very similar to those of the Land Surface Water Index (LSWI).