Where, T
s
is the earth’s surface temperature of a given pixel in a featured space; NDVI is the normalization vegetation index value of the pixels; T
s max
and T
are the surface temperatures of the dry and wet edges corresponding to the NDVI, respectively; and a
1
, b
1
and a
2
, b
are the slope and intercept of dry and wet edge equations, respectively, which can be obtained by linear fitting. The TVDIs calculated by using this formula are the normalized values, between 0 and 1. Larger TVDI values indicate low soil moisture and high degrees of drought, whereas smaller TVDI values
2
s min