Snow and ice classification

i’m working with snow masks extract from LQSF file. I’m having some difficulties to find out the algorithm on which the classification is based. Is it based on the so called ODSI index? Or it uses also data from SLSTR sensor to implement a classificator of the snow similar to the one used by SPOT VGT?

The best document which describes the classification is this one:
Sentinel-3 OLCI Alternative Atmospheric Correction ATBD

It is said that ONSI is used for the classification of snow/ice.