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Mike's Muses occasional articles...
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mikealder
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Joined: Jan 14, 2005
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Location: Blackpool , Lancs

PostPosted: Sun Mar 18, 2007 1:41 pm    Post subject: Reply with quote

p800 that is similar to the methods a few of us have mentioned, however I am a little concerned as to the explaination of why GPS won't work underwater!
Quote:
GPS doesn't work underwater, as the signal cannot reach the satellite from a submersible

The GPS is the receiver not the satellite, but I guess the rest of it is accurate - Mike
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40apple40
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PostPosted: Fri Mar 23, 2007 6:54 am    Post subject: we use pingers Reply with quote

alncc1701 wrote:
Don't know much about the technicals but these guys claim they have underwater GPS

http://www.underwater-gps.com


Al


hi,

here's some info that may be of interest.

i'm a subsea engineer / R.O.V pilot. R.O.V stands for remotely controlled vehicle. the vehicles are fitted with cameras, sonar & beacons (pingers).
the vehicles are used to go down to as much as 3000m water depth, to lay, bury & repair telecoms cables, power lines & pipelines.

positioning of the cables & pipelines is critical, as is the location of the vehicle. this is ascertained by a similar method to the quote above - the R.O.V is launched from a surface vessel equiped with Differential GPS (a more accurate form of GPS accurate to a metre or so) & an accoustic receiver/transmitter.

during a dive, the ship will transmit an accoustic ping on a channel specific to the pinger (also called beacon or transponder) on the R.O.V at a settable rate of maybe once a second.
this causes the R.O.V pinger to be interagated & it will respond by emitting a reply signal. this reply signal is decoded by the receiver on the ship (using the time delay & known speed of accoustics) to give an accurate position relative to the ship & depth (to just a few metres but i'm not sure of exact figures - normally, cotracturally this needs to be within 10m though).

obviously, the ships positon is known. during diveing ops a navigation screen is used that displays graphically the location of ship, R.O.V & work site so while flying the R.O.V it can be a bit like playing a computer game (a crappy one that is).

if there were enough surface gps receivers then under water positioning would be generally possible if the person under water had a receiver to decode the surface ping signal.
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40apple40
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PostPosted: Fri Mar 23, 2007 7:04 am    Post subject: we use pingers Reply with quote

forgot to mention that the receivers used on ships are directional, so is knows the bearing of any transmitted signal.

i'm not sure about all the technicalities but because only 1 receiver & one beacon is required with these systems to get an accurate 3D position of range, bearing & depth.

hope i didn't waffle on too much.
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40apple40
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PostPosted: Fri Mar 23, 2007 7:14 am    Post subject: we us pingers Reply with quote

hello again - here's a link that explains things better than i can:
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gascap
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PostPosted: Sun Sep 21, 2008 2:39 am    Post subject: underwater gps Reply with quote

Underwater GPS

I have an idea that I have been working on for underwater gps its alittle crude but I think for all practical purposes it should do the trick. It will work on 2 parts one from a dive boat transmitting a ping for sonar and update the next is a cute little dive computer that will send out periodic pings to find the boat or bouy transponder and update a position with depth and profile even update current position and adjust for current and depth a downloadable scan of the ocean bottom from a larger piece of boat mounted equipment and you can have a visual map on your dive giving you original position and boat position against the backdrop of a topographical map. anyway its a work in progress. Still waiting on some financial backing to move things alittle faster.
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