NDWI is useful to assess water content in a normalised way. This index increases with vegetation water content or from dry soil to free water. The SWIR reflectance indicates changes in soil and vegetation water content, while the NIR reflectance is affected by internal structure of leaf and soil but not by water content directly. The combination of the NIR with the SWIR removes variations induced by internal structure of leaf and soil, thus improving the accuracy in retrieving the vegetation and soil water content