IR = (R - G)/(R + G)
It uses the following data: channel green (G) and channel red (R).
The soils with a very light gray outcropping gypsum crust (low IR), the
soils with aeolian sail, composed of reddish quartz sand (high IR).
When; under the combined effect of agricultural practices, the wind, and
their deposits move, the composition of the soil surface is modified and
their color as well. By following the variations in the redness index,
it is then possible to follow these modifications (Escadafal and al.,
1991). The soils and mineral surface materials are the dominant
components of arid surfaces; the interpretation of images acquired by
satellites over these regions requires knowing and taking into account
the corresponding spectral properties. Information of a geological and
ecological nature can be drawn from it, by detecting the presence of
outcrops of clear materials (limestone, gypsum, salts, etc.), or sand.
Only a knowledge of the environment and its different aspects according
to the level of degradation makes it possible to use the index IR to
diagnose a possible evolution of the state of the environment, positive
or negative (Escadafal and Huete ,1991).