I'm not aware of any specifically, but one of the instruments that can be used as a data point to further reduce error when navigating in a zero-GPS/zero-radio-

I'm not aware of any specifically, but one of the instruments that can be used as a data point to further reduce error when navigating in a zero-GPS/zero-radio-signal environment is an INS. The very highest precision ones are quite classified and used on submarines. https://en.wikipedia.org/wiki/Inertial_navigation_system https://en.wikipedia.org/wiki/Inertial_navigation_system