VARI was originally designed for satellite imagery. It is a vegetation index the uses only light waves from the visible light  section of the spectrum (Red, Green, Blue). It puts a quantitative value on vegetative fraction estimation (VARI = (Green – Red) / (Green + Red – Blue). The index is only affected by atmospheric conditions a small bit so it can be applied in a wide variety of environments.

Reference:

(Last Edit 6 Feb. 2023, Kellee)