These photos show the probes currently used on aircraft to detect icing. They’re some of the metal rods protruding from the planes. In one of the most widely used probes, the probe vibration frequency changes as ice accumulates in it. This method is the best technology available today, but it does not work well in some of the most severe icing conditions.
An IVS technology, originally developed for use in space, optically detects icing encounters that the current technologies can’t. This includes the more than 1 in 100 icing encounters that fall outside of the “classic” icing certification envelope (14 CFR Part 25, Appendix C).