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Patent Filed for Underwater GPS
Matthew Sparkes writes "GPS doesn't work underwater, as the signal cannot reach the satellite from a submersible, but researchers have now patented an add-on to the system that could provide GPS navigation for submarines. A base station is tethered to the sea bed at a known depth and GPS location. A submersible anywhere in the area sends out a sonar pulse to which the base station replies with a signal, giving a GPS position and depth as well as the bearing angle from which the submersible's request arrived. The submersible then uses its own depth, which is easily measured, plus the round trip pulse time and the bearing angle sent by the base, to calculate its own position."
Little nit pick ... GPS signals go from the satellite to the receiver not the other way around.
What is the current mechanism of position-fixing used for subs? Or is it more of the 'traditional' type of navigation where you know where you started, what direction you travelled, how fast and how long?
Subs have highly accurate inertial navigation systems. I've seen one on of the labs at Stanford where they develop the sensors, and it's amazing. It's kind of like a warehouse, with one of those huge 20 or 40 ton cranes. They use the crane to haul large masses around, and the sensors are able to detect the variations in the gravitational field caused by those objects.
On top of that, the navy has all sorts of charts of the sea floor, many of which are probably classified to some degree or other. Subs can use "landmarks" on the sea floor to determine their position. Since highly precise navigation is usually only important in coastal waters, this works pretty well.
Filing a patent application does not mean that you have "patented" something. The link in the summary takes you to a patent application publication. Patent applications typically publish 18 months after they are filed (or in this case, 18 months after the earliest application to which priority is claimed). With USPTO backlogs, it will probably be 5-7 years before anyone at the USPTO even looks at this application and "patents" this invention.
This thing is not GPS. It is sonar ranging that just happens to also includes the GPS locations of the bouys to help give a true position. Doing sonar positioning requires that you know where the bouys are and GPS provides a very good way of doing this.
Engineering is the art of compromise.