How it works
How underwater GPS works
Underwater GPS relies on a series of base stations, which are tethered to the sea bed at known depths and GPS locations.
A submersible, or diver, is equiped with a device which emits a sonar request pulse designed to communicate with the base stations. If a base station picks up the pulse it replies with its own signal containing the following information:
* the base stations GPS
* the base stations depth
* the bearing angle from which the signal was received
Upon receiving this information, the device takes a reading of its own depth, along with the round trip pulse time, and a simple calculation pin points its own position.
See the diagram on the Underwater GPS homepage