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."

Which way do those signals go?

[goofy183]

Little nit pick ... GPS signals go from the satellite to the receiver not the other way around.

GPS is passive

[Anonymous Coward]

GPS doesn't work underwater, as the signal cannot reach the satellite from a submersible

GPS is a passive system, the device never sends a signal to the satellite. Of course that mistake is widespread, as TV and Movies always show 'GPS trackers' that do just that.

Re:Stupid question ....

[tbo]

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.

Re:Which way do those signals go?

[Anonymous Coward]

Yes, GPS signals go from the satellite to the receiver - the receiver in this case is the buoy, which uses the satellite signal to compute the buoy's location. The buoy sends its own computed location (along with bearing angle information) to the sub (or whatever pinged it). The sub uses the buoy's location, the bearing angle, the sub's depth, and the elapsed round-trip signal time to calculate its own position.

This isn't patented....summary wrong

[kansas1051]

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 is not GPS!

[EmbeddedJanitor]

I didn't RTFA (that's cheating), but the summary is a crock.

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.

Re:Stupid question ....

[Anonymous Coward]

As of the mid-80's, the Lafayette class FBMs used SINS (ships inertial navigation system) that used some sort of strain gauge to measure movement relative to some seriously hefty gyros spinning at crazy speeds. Even with that system, there were still times when we'd come near the surface to run out a trailing wire antenna and get a satellite fix to be certain of location.

If you mess up your location calculation by even a little bit at the time you launch the missiles, the error tends to be a bit larger after two or three thousand miles where the missile goes boom. It's always a good idea to have a couple of position references just to be sure the boom occurs where the boom was intended to occur.

An old FBM (floating ballistic missile platforms) could not use the system described because they simply did not ping unless there is was critical need or a functional test is required. We had about a dozen passive sonar systems but only one active navigational sonar system and the power switch that controlled the high voltage required to use it had a padlock on it. It could not even be powered up unless the OOD unlocked it. I saw it used once in four years, the captain thought it would be fun to try and locate a shipwreck in the channel while we were transiting on the surface.

Newer boats may have improved equipment for doing discrete pings but pinging in general is a very bad thing to do since it gives away location. If the locations of the GPS buoys/beacons are known then it would basically be giving away the whole show as undoubtably someone would drop some microphones in the area to listen in and learn about any potential traffic patterns.

As long as the boats don't ping, there will always be only two kinds of ships in the Navy. Submarines and targets.