The NDISIndwi operator algorithm computes the Normalized Difference Impervious Surface Index with NDWI from a given product.

The NDISIndwi results from the following equation:

NDISIndwi = (T - (((G - N) / (G + N)) + N + S1) / 3.0) / (T + (((G - N) / (G + N)) + 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 'ndisindwi_flags' with the following bit coding:

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