Underwater GPS

[alo100]

The principle of multi-pingers is already used in the oceanographic industry. In fact, the receiver estimates its relative position to the different pingers. Assuming the precise position of each pinger is known (lat/lon), is not very complicated to triangulate the lat/lon position of the receiver.

Unfortunately, these method is dependant of an emitter underwater. A real underwater GPS would be independant of any emitter except the satellites. A solution would be to have a surface calibration with lat/lon and then measure the displacement underwater. Not at all simple but some offshore/military solutions exist with the same principle.

I have seen the on land versoin of it using both pingers and GPS.
For GPS to work, we need to recieve relatively clear signals from 3 satellites which is not always possible, when this happen, the system would then switch to use the pingers -- measuring the relative strengths from the closest pingers to approx. the locatoin of the target instead.

 

[TerryInFlorida]

There are a number of things this would open the door for.

One you could track your boat while diving, there could be an anchor drag alarm set to work between the boat and your underwater unit, could be handy...

Two, the person on the boat could track the divers and possibly have a remote setup for emergency contact between boat and diver for various reasons...

Future inventing could consist of an alarm setup warning other boaters of divers down and location, so as to not tread on divers while speeding around... Kind of a gps diver down flag...

I don't know how far fetched the ideas are relative to gps? I had the idea of having the gps stationed on the boat and then using some type of sonar to send information of location and such to and from the boat, with alarms that you could set to warn you when you were wondering too far from the boat or distressed and such...

 

[thedaddy]

check this web site before you spend a lot of money
http://groups.msn.com/divergps

I really like the idea of being able to mark and return to a spot.
I talked to Mark and read his work. It is practically effective and economical (KISS). I didn't implement his whole design, but an otterbox, a handheld, and reel will get you a long ways for cheap. I have a magellan sportrak that works decent (also waterproof to a degree). A pause with the unit at the surface will give you a track marker for an implicit waypoint, although you need to figure out how to sort and correlate all your data on the surface (it is easy to lose track of more than a few datums). If you do a good job of taking notes on each deployment in a given dive, then you can create your waypoints file after the fact using software. If you want to get really fancy, you can go the whole 9 yards and put in the buttons to navigate the input screens and menus on your gps in realtime underwater on each deployment of the gps.

I still haven't seen a good way to overcome the current drift issue, other than recording line length, depth, and approximate current bearing from the small surface track you get when the gps deploys. Basic geometry will get you a fairly close approximation for submerged position relative to the actual surface position of the gps. That's a lot of bookkeeping under task load and less than optimal conditions; but if you need to get a fix on an underwater location, it's effective (should get you within ten yards of your target). Search skills will be needed from there...

Mark's is about the most practical setup I have seen, if you don't mind setting it up yourself.

 

[Jmaserati]

I love all the ideas expressed here - lately I've been using GPS at work and it's starting to give me ideas for more practical applications for divers. When I've really thought them out, I'll share them here.

I also plan on using my contacts with the GPS industry support folks to ask them what they think about diving applications.

(I'm currently working as a land surveyor)