Being decidely land-dwelling creatures -- our only real underwater experiences were some nasty childhood dunking incidents at the local pool -- we've got no real use for determining our location beneath the waves, but apparently the folks who drive around all day in submarines do, so the US Office of Naval Research has whipped up a relatively simple method for "geophysical positioning" when satellite GPS data is inaccessible. You'll recall that we recently saw another patent
which claimed to offer the same functionality for above ground, indoor locations, but that involved using surface-level receivers and ceiling-mounted repeaters -- a setup not possible when satellite signals can't penetrate deep underwater. The ONR's solution is to anchor an undetermined number of transceivers -- whose exact spatial location is already known -- to the ocean floor, and then by comparing the angle and distance of broadband acoustic signals sent back and forth to moving craft, using some basic geometry (sounds like our man Pythagoras comes into play here) to determine where in the world that sub happens to be. Seems pretty obvious when you think about it, but maybe that's we're covering this tech secondhand instead of trying to hack it as naval engineers, marine cartographers, or whoever the heck it is that comes up with this stuff.
[Via New Scientist