Underwater GPS (sorta)

Posted Mar 13th 2008 2:01AM by Will O'Brien
Filed under: gps hacks

Since water blocks the radio frequency used for GPS triangulation, GPS is considered pretty useless for SCUBA divers. Apparenlty some of them are finding it useful to waterproof off the shelf units for tracking the beginning and end of dives. (Dives in open water often involve currents that can really move you along.) To avoid any wiring, a floating case is used. When the diver wants to grab a waypoint, he/she lets the gps surface for a short while to acquire a fix. Then the diver can pull it back down and mark the waypoint or record the coordinates.

Reader Comments

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1. As a scuba diver myself, i think that this is an excellent idea... a way to know where you are in relation to your surroundings (although you really should know already, but nobody is perfect).

Posted at 2:33AM on Mar 13th 2008 by Abbott

2. many gps units can accept an external antenna...how useful/difficult would it be to have a buoy and tether with gps antenna up top for continuous tracking? possible tangle hazard? what about measuring the water pressure and inserting a negative altitude value in the NMEA stream, hooking into a waterproof camera, now you can track the whole dive and place photos on the path.

Posted at 3:36AM on Mar 13th 2008 by macegr

3. @macegr
The problem with a tether and buoy system is if any slack is in the tether then the buoy can drift away on a surface current most likely in a direction other than your own. Loose tether = random buoy movement.

Posted at 8:11AM on Mar 13th 2008 by Nick.B

4. As a diver and a geek (lvl 70 Pally)I have to say WTF.
I have done dives in oil (tanker hulls) and I had a pretty good idea of where I was. Off hand I can't think of an application for this other than " we do what we must because we can". I would rather see a portable waterproof sonar device for tracking big beasties. Charcharodons for example.

Posted at 11:26AM on Mar 13th 2008 by Ackphlat

5. @ackphlat

Too much like the alien movies for me... I'm the paranoid type. Every blip would be coming to eat me.

Posted at 1:26PM on Mar 13th 2008 by Spadefinger

6. ha! when i first glanced this story on my feed list i thought it said underwear gps. can somebody get working on this?

Posted at 1:28PM on Mar 13th 2008 by paul

7. @ackphlat

First, I am not a diver, but...

I don't think the idea is for something like a ship dive. In the description he brings up open water dives with current involved. In those instances, I can see it being useful. Also say you come across a point of interest. Wouldn't it be more convenient to be able to send up the GPS and take a point, so next time you can easily start there?

Posted at 2:05PM on Mar 13th 2008 by pt

8. I, too, am a diver and I agree with @ackphlat and others - being able to mark a point of interest on a long dive is an excellent idea.(rebreathers are good for up to 10 hours)The problem with floating antennas is described above and whoever can up with the simple solution of temporarily floating the GPS to the surface was brilliant! One has to wonder what you do with the 100' of line after you retrieve the GPS unit, though. Do they make corrosion-resistant fishing reels?

Posted at 5:11PM on Mar 13th 2008 by SciFiDiver

9. i havnt read the link yet, but I would guess that a good use for it would be mapping and locating "items of interest" on the seafloor, etc. I cant imagine that dive maps are %100 accurate nore all inclusive. GPS would be of deffinate use to sport divers who dive the same areas often.

Also, very usefull for marking accurately the placement of experiments.

anyway, I would think that, as mentioned, 100 feet of bouy line would be a pain in the ass for a diver to manage. How about a corrosive resistant compact electric powered fast winch to pull this thing back down to the diver again?

Posted at 11:41PM on Mar 13th 2008 by MRE

10. LOL, now underwear GPS is something I can see many uses for! For a shallow dive I suppose it would prevent going to the surface to mark a waypoint but no way will it work on a deeper dive in a stiff current for several reasons. One, the current will pull the device off the mark so if you are at 80' the device may surface 60' upstream of your location. If you tried you could not make it surface directly overhead. Two, no way am I dealing with 200' of line at 100' with a current. The 15' on my Mares is enough to deal with. Three, God invented compasses for open water dives. For points of interest, I do know where I am without a GPS. Now start working on the underwater sonar and the underwear GPS!

Posted at 10:02AM on Mar 14th 2008 by Ackphlat

11. Managing the required line?

Nobody heard about http://www.diverite.com/products/catalog/reels reels?

Posted at 10:07AM on Mar 14th 2008 by João Silva

12. Just to note, gps is accurate to 50ft/15meters. So a tethered antenna surfacing 60' from your point wouldn't matter much.

Posted at 5:38PM on Mar 16th 2008 by cde

13. As a diver who isn't perfect, this sounds really good to me also.

It might also be good for marking spots to which you hope to return in the future.

Posted at 8:36PM on Mar 21st 2008 by Tom

14. I have used this for years as a diver. I am working on getting the antenna and a calculation for the error on the floating antenna based on the diver depth. I'll let you know once I have it figured out.

Happy diving...

Posted at 8:32PM on Mar 22nd 2008 by DiveMichigan

15. As you can see someone is already making an underwater gps. The main reason I know of using this is for underwater surveying.

The comment about the accuracy of gps's is wrong. I average 10ft (3 meters) when in waas mode. This varies on coverage too. This is with a garmin fortrex 101.

Posted at 6:06PM on Mar 26th 2008 by eco diver

16. Why not use three or more buoys randomly placed on the surface, each with their own GPS and a transponder to do "LPS" based on the buoy positions. Think of the buoys as being local GPS satellites themselves, on different frequency that will penetrate hundreds of feet of water easily. They could then report back to the main buoy node connected to the dive boat which would report the location information as calculated by all the differential signal timing information - exactly like GPS does it globally - and offset the known GPS surface points by the relative distances from each buoy location.

Eventually dive clubs could install semipermanent buoys in popular areas for public use. Call it "DPS" (dive positioning...)

Posted at 5:39PM on Apr 7th 2008 by Spudz76

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