Underwater GPS

[Inspector#2]

About 3 years ago one of the LDS had a 2 or 3 piece set that I believe was a gps navigation set. The "floater" was the receiver for the gps. Somehow it communicated with a carried device the diver would have. Can't find it on the net anywhere but at one time it existed. If my memory is intact it was around $800.

Dave

Found a similar system but I don't remember the cable.

http://www.longbeachdive.com/product-concept-swich.htm

 

[Al Mialkovsky]

That is the buoy that you tow to use a gps underwater. You rich? It's a waste and I'm not a tow boat.

I am also a geocacher and have found underwater caches using a gps. But the coordinates took me to a site on the beach. From that spot I had to snorkle directly towards the northern tip of Lanai and when spotting the cache site from the surface drop down and log it.

King Kahekili

 

[kayakdiver]

have been using a simple approach for over 3 year
(published in Underwater Mag. nov/dec 02
info at http://groups.msn.com/divergps
**No power cable/antenna set-up is needed
I gain "updates"...Only as needed ...to keep an eye on the anchor position...and to mark points of interest
Problem? very....very....very..few divers will try something new
before they see scores of others using it.
I'm promoting this as an academic project
*Not a theory...used constantly with fantastic results

 

[pggeek]

I was thinking of putting in some underwater catches Glad to see someone has done it.

Dam now I have to find a underwater case for my Garmin V. so I can swim to the spot, then dive to the catch.

Jason@programmergeek.com

 

[DA Aquamaster]

I have a Magellan sport track that is waterresistant to 10 ft. and accurate within 3 m or so under ideal conditions (when a WAAS sattelite is available). I will attach it to my dive float (it gets better reception if mounted upright) and tow it along on the dive. Assuming I keep the line tight it remains more or less above me and I can mark sites in a manner of speaking as long as I make a sharp 90 degree course change at the object and swim 50 ft or so from the object so that I can see clearly see it's location on the track after the dive. You can then scroll back along the track and mark the spot from the surface after the dive.

It at least lets you know where to park the boat on the next dive but is not of any use in navigating once you are underwater.

I don't see why a housed GPS would not work as long as you used a remote antenna on the surface and ran the wire down to you on (or as) your flag line. You would need to keep it tight though to keep the float above you. (lets see... $300 for the GPS, REALLY big $ for the custom Ikelite housing...)

 

[jplacson]

DA Aquamaster once bubbled...
I don't see why a housed GPS would not work as long as you used a remote antenna on the surface and ran the wire down to you on (or as) your flag line. You would need to keep it tight though to keep the float above you. (lets see... $300 for the GPS, REALLY big $ for the custom Ikelite housing...)

You have to understand how a GPS receiver works to begin with... but with your idea of keeping a tight line to the surface..you're kidding right? Not even a metal rod could hold a straight line up at depth... unless you only plan to dive down to 10 feet or so... or have a metal tube that's about 10' in diameter. Any length of cable, wire, rope will be towed behind you...no matter how tight you get it.

Now back to how GPS receivers work... running A remote antenna will work... IF a GPS only used ONE antenna. The only way an idea like that would work is the way UnderWater GPS works... the buoys have GPS receivers each... then each buoy must relay it's position down to the underwater GPS, which must then recalculate it's position based on it's relative position to the bouys (at least 3 must be used for proper triangulation) then adjust to calculate proper GPS position based on buoy positions.

You're idea of running an antenna relay would work... IF you ran 12 (a modern GPS receiver has a 12-channel parallel antenna...meaning it can track 12 satellites for positioning... and MUST have a MINIMUM of 4) lines to the surface... and have separate relays for each antenna... but that wouldn't give you YOUR position, it would give you the position of the buoy or floating antenna.

 

[jeremyrfoster]

Wait a minute, John. I realize that modern GPS's have arrays of antennas, but they are packaged in a single unit... are they not? You can purchase an antenna (array) for your car/boat that you slap on the roof as a single unit. It's not like you have to have 4 wires going from your receiver unit to your roof.

 

[jplacson]

Actually the antenna extension has 12.

And when you do attach the antenna to your car or boat... the GPS display tracks the BOAT/CAR... not the unit itself anymore... the GPS will track the point where the satellite signals hit the antenna... not the unit that calculates it.

Now I think it's kind of pointless to have a GPS system that doesn't track your location...and just tracks a floating buoy don't you? You're better off with a normal buoy and buy a NeverLost system to find your way back.

Accurate GPS readings will be off since the floating antenna relay will ALWAYS trail behind you... or to your side...or whichever direction the current takes it... not to mention potential snag problems... cuz unlike a guideline, which doesn't move... you will HAVE to drag this antenna buoy around to get your position right? Since the GPS is tracking the buoy/relay and not you. If you go to the UnderwaterGPS site, you'll see that this is basically what they do... except they deploy 3 - 4 relays at different locations to act like satellites themselves... then teh GPS calculates based on triangulations from the 3-4 buoys.

trailing a non-fixed antenna relay will give you very inaccurate locations readings... maybe as far as a 60 foot radius... or at BEST 25 foot radius if WAAS is available.

 

[Charlie99]

jplacson once bubbled...
You have to understand how a GPS receiver works to begin with...

... IF a GPS only used ONE antenna.

... IF you ran 12 (a modern GPS receiver has a 12-channel parallel antenna...meaning it can track 12 satellites for positioning... and MUST have a MINIMUM of 4) lines to the surface... and have separate relays for each antenna... but that wouldn't give you YOUR position, it would give you the position of the buoy or floating antenna.

Even a 12 channel GPS has 1 and only 1 antenna. The GPS system uses code division multiplexing where the different satellites are detected using correlation techniques similar to that of the CDMA celluar system. A single coaxial cable is sufficient to connect the antenna with the main GPS unit.

 

[jeremyrfoster]

Charlie99 once bubbled...
Even a 12 channel GPS has 1 and only 1 antenna.

Now that sounds right! Thanks, Charlie99.