The NDISIg operator algorithm computes the Normalized Difference Impervious Surface Index Green from a given product.

The NDISIg results from the following equation:

NDISIg = (T - (G + N + S1) / 3.0) / (T + (G + N + S1) / 3.0)

, where:

The bands are:

- G is the Green band
- N is the NIR band
- S1 is the SWIR 1 band
- T is the Thermal band

Also the processor computes an additional flags band called 'ndisig_flags' with the following bit coding:

Bit Position	Description
Bit 0	The computed value for NDISIg is NAN or is Infinite
Bit 1	The computed value for NDISIg is less than -1 (minus one)
Bit 2	The computed value for NDISIg is greater than 1 (one)