Underwater GPS

[Don Burke]

Submarines use mast mounted antennas for GPS, including periscope mounts. Yes, it is normally a single antenna, although some precision machines will use two to better pick up the two frequencies used. No one has been able to make a trailing wire work reliably at those frequencies.

LORAN, on the other hand, will penetrate a few inches of seawater. The wire and masts just below the surface will pick up the 100 kHz signals to some extent.

For diver navigation, those hand-held gadgets show some promise. I think they need considerably more development before they become more than a get-home beacon.

For deep submersibles, a field of transponders is set, surveyed, and used for local navigation. It's pretty time consuming.

With the advances in electronics, there should be a way to have beacons on the surface with GPS input so the field would be self surveying. The system would work much like an audio version of LORAN with the beacons also sending updates to the diver units so the varying positions of the beacons could be accounted for.

Anybody got a few million burning a hole in his pocket so we can do some R&D?

xxxxxxxxxxxx

I've seen the waterproof box that you put a handheld GPS in so you can send it to the surface from time to time. That strikes me as clumsy. I'd prefer to leave the GPS on the surface and have a link to a display the diver could hold. The link could be audio or even fiber optic, since the diver would have to tow the buoy around by something anyway. If the horizontal trail distance was an issue, the dive could pull the line as close to vertical as practical for relatively precision readings when needed.

This one would be much cheaper, but dragging that buoy doesn't have much appeal unless you are required to drag a marker anyway.

 

[JGB560]

Ok there is something called false GPS that one of the posts mentioned here. Its basically a GPS receiver mounted in a buoy. Attached to the buoy is a hard wired waterproof display that a diver carries showing the receivers position. The buoy is towed by a diver. It is called false GPS because it gives the position of the buoy, not the diver. The error is dependant on the amount of line from the float (buoy) to the diver and his vertical position from the center of the buoy. For deep dives in strong currents such as a tide or rip current it could be 100ft or more. The GPS satalites are sending (transmitting) there RF signal (1.5 GHz signal) down through free space ( line of site). The GPS uses multiple signals from several satalites to calculate its position. Now the first reason that regular GPS doesn't work underwater is because the 1.5 GHz signal is a high frequency radio wave. These waves do not penetrate solid or liquid media (water) very well. This is why your older 900MHz phones works a little better in your house then the 2.4Ghz phones even though the reverse is true ouside. However lower RF can penetrate solids and shallow water better. The navy uses ULF (ultra low frequency) comunication from ships to subs for this reason, but the sub still has to come up to a shallower depth (150ft or so) and float a buoy with an antenna. The second reason is that the system is data hungry in the sence that data is contiounsly be transmitted from the satalites.
There is a system being developed that uses acoustic waves (SONAR) that solves both of these problems using the GIB technology. First because sound travels 4 times faster in water then air, sound waves can move more easily through water. The GIB system uses multiple surface SONAR buoys in each major body of water. Second the sonar signals are sent from the buoy to the receiver only when a request for data is called for by the receiver, thus eliminating the continous downlink of data. And the data to individual receivers is time or frequency multiplexed. This allows for a large number of receivers to gather there individual positional data with out any signal conflicts.

 

[MaxAlegraD]

GPS underwater is something very far from reality mainly because of the error that is intrinsic to the GPS system + the error generated by using solutions such as attaching the GPS unit to line and letting it float.

Normally GPS units generates errors in measuring positions in the range of a minimum of 9ft. My experience has been between 18-45ft avarage.

Well to get coordinates of a wreck or some place that you want to return that error is ok.

If we add to that an error based on the depth and strong currents we can end up with errors above 60ft very easy.

If an avarage error of 60ft if ok than go for it ! You have a new toy in your gadget list for underwater exploration. But remember that when you plot the coordinates of the map you can get wrong reading on any direction (N,S,W,E). The map can get really messy.

For those who need more precise readings only the use of a single coordinate and the use of a fixed GRID can help. By doing that you reduce the error sampling by simply adjusting the coordinates of your grid to the base coordinate. Something like a Differential GPS.

 

[ba_hiker]

military uses inertial navigation for many things including subs. it predates gps by several decades. it does not require an outside refrence, just a precise knowledge of where you start, in precise measurements of the directions and distances traveled. gps is used to get the starting position.

the precise distance and direction measuring insterments used to be very complected and expensive, but now are being built on a few chips (mems).

 

[IslandHopper]

You should be able to get a used INS out of an old "retired" 727 ... get someone to make a housing for it and take it under with you.

Of course that old (read "affordable") model will probably require a housing the size of your kitchen sink and weigh on the order of 100 lbs .... but you'd have accurate underwater nav !!!!
... of course, the read-out simply gives Lat and Long ... no moving map or color screen

 

[NAM001]

I figure the Navy has to have developed somehing to assist with undewater navigation. I was thinking along the lines of of ULF wave triangulation. The problem with that is that those waves travel at different speeds through waters with differing salt content which would make the system fairly inaccurate without a very large number of reference points. Also ULF waves have been linked in a corrolary (not causal) fashion with disruption to marine life.

runvus4

you are right about the navy however the others are right also. LF coms is still radio and needs antenna on the surface or close to, as in the gps. to make a radio device work reliably is going to be expensive. your reasonable alternative is a sonar related device like suggested. if ou are any where adaquate at navagating (one minute = 1 mile n/s) you can use a sonic locator. the expensive one that gives direction and distance (not signal streignth) and plot from a known point. it has more than enough range to it as compared to air limitations and the distance you can go with that air. it would be far more accurate than the sonar ulf concept as the speed of sound variations will not give you the accuracy you would want let alone the loran similar issues that would have to be delt with by redundant signal sources that the environmentalists would not like.

regards

KWS retired submariner

 

[Bubble Blower 479]

My Garmin Rino 120 is waterproof for 30 minutes in up to 1 meter of water. You can't take it underwater, but you can keep it on a float above water. It can keep a record of where you have gone.

 

[archman]

My Garmin Rino 120 is waterproof for 30 minutes in up to 1 meter of water. You can't take it underwater, but you can keep it on a float above water. It can keep a record of where you have gone.

Most Garmin GPS units have this weatherproofing standard. I would be extremely wary of floating one on the surface however. Besides, I think the submerged waterproofing measure assumes that external power/data ports are not in use and plugged up. You'd need these open in order to say, run some sort of data screen on a submerged tether.

 

[BlueDevil]

The latest issue of of Scuba Diver (Australasia) has the following short piece:

"Chinese scientists have developed the first high precision underwater global positioning system (GPS). Tests have shown the new system can detect horizontal position within 5cm and depth precision within 30cm."

That is the only information given so I can't elaborate further.

 

[BlueDevil]

Further to my last post have a look at: http://news3.xinhuanet.com/english/2004-01/11/content_1269648.htm

Doesn't sound like something a diver could use.