Different VIs such as NDVI, ANDVI, MSAVI and SAVI may have
different linkages with LST providing the design basis of the VITT.
Sandholt et al. (2002)pointed out that the simplified triangle space
of LST–NDVI may exhibit the soil moisture contours reflecting the
spatial patterns of the VITT. It led to the definition of the TVDI as
expressed below: