GPS is a powerful navigation technology, but it doesn’t work as well inside buildings, underground or underwater. Now engineers in Japan have developed and tested an alternative technology that uses cosmic rays to track movement beneath a building with precision of a few meters.
Interesting idea, but if I understand this concept correctly you need an RF link between the four base stations at the top and the underground unit to correlate muon detection events. This might limit the usefulness/range due to RF interference and obstruction. At the same one could just use normal correlated RF signals from all stations to pin point the underground relative position.