Underwater GPS

[DrDuktayp]

A friend of mine that doesn't dive thought I should make some kind of floating antenna for a GPS. I just dismissed the idea as nuts.

DrDuktayp

 

[Jmaserati]

Check out the divergps site at MSN as mentioned above, and also check out this site guys:

http://www.geodiving.com/

I'm into Geocaching too! www.geocaching.com

 

[Scubacastor]

Hi,

I already used a GPS underwater. In fact the GPS receiver remains in surface and transmit information to some sort of display device with embedded electronic map. Targets can be selected while underwater and the positions are logged and then uploaded in a desktop computer. The link may be a electric or optical cable. I know some people are developping the same systems but using ultrasonic transducers. This kind of technology is quite far from what hobbyists do. I have also heard about a commercial unit in the US called Scubanav.

I won't tell more details as I am involved in one of these projects

ps: By the way, I say hello to "DIY divers". I am new in this forum but I have built some DIY stuff. Have a look at http://eocean.free.fr/projects/ (unfortunately all is in French)

 

[The Kraken]

Jonnythan wrote:
"Why on earth would you want to do this?"
??? Ever done any underwater archaeology and wanted to come back to the exact same small spot without having to use up several tanks searching for it ???

Hidiver1 wrote:
"One of these days, someone will market a surface float/GPS antenna, a reel with line having a metal conductor cord core, and a GPS in an Otter box or underwater housing."
--- Alread been done. Forget the name of the company, but they sell something just like that. The antenna sets in a waterproof case on the surface in a ring buoy type of device. An antenna cable is run below the surface to the GPS unit which is enclosed in a water tight housing. The down side is having to tow the antenna unit about with ya.

 

[Scubacastor]

Yes, it's ScubaNav : http://www.longbeachdive.com/welcome.htm

 

[Desa]

What is your most efficient method for compass reading on your scooter? I have to stop to read mine because of the magnetic field from the Scooter?

not wanting to hijack this thread, but I thought I would address this issue:
The magnetic field remains constant. If you play with your compass and scooter you can come up with a degree of error that will always be the same.

In layman terms: If you hold your compass in the same place (with respect to the scooter) each time and you know it is off by, say 3 degrees west, then you can adjust this on the fly while underwater.

Only excetion to this rule is if the field locks the north seeking arrow up. In this case you will be Libra Oscar Siera Tango (lost)

As to using the gps unit in a sealed bag and pulling it on the surface, it works. When you get home you can download to a nautical mapping software and start "painting a picture" or a roadmap of the local dive area. Usefull when giving dive briefings.

Just my 2 cents worth.... :11ztongue

 

[scubanav]

The only problem with that the towed GPS, if you are say in lets say 65 feet of water, with currents you will need twice that in line thus making your position far less accurate. Sure it may get you within 70ft or so but not good enough to do what you want. I am a offshore surveyor and all I deal with is acoustics and GPS. I am currently working on developing one myself. I Have a few ideas that could make it work.

 

[Warthaug]

I've thought about GPS-like underwater navigation many times before, and there is always the problem of radio wave propagation through water. Either they don't make it, or their wavelength is so long as to be functionally useless. But there may be a way, with sound, although it would require setup before a dive.

I'm not sure how many people here are familiar with aviation navigation, but there is a form of radio navigation (VOR) which could potentially be modified for use with sound. Basically you have a rotating sonar beam, which makes a 360 degree in a set period of time. Every time the beacon passes a set point (say magnetic north) it emits a pulse on a second frequency. By measuring the time between the pulse and the sweep you can determine your bearing relative to the station.

Use two stations far enough apart and you can triangulate.

Easy in theory, but implementation...

Bryan

 

[Scubacastor]

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.

 

[Warthaug]

Unfortunately, these method is dependant of an emitter underwater.

But it would be a simple matter to have a transponder permanently mounted on a boat (if boat diving). Even setting up a couple of transmitters on anchored buoys would be just as easy (and probably safer) as having to drag a surface line throughout a whole dive.

It is possible to do this with a single transmitter, although you now need a diver-mounted pinger. Would make the system even simpler to setup, although the complexity of the divers unit (and it's cost) obviously goes up.

At the end of the day you’re stuck with the choice of towing a surface station of some sort, or setting up some sort of marker system. Both are a pain, and the surface tether has the potential of being a hazard to the diver. It’s an interesting problem, although to be honest, I’ve never felt the need for such a system myself. A map & compass is all I’ve ever needed.

Bryan