I have been looking into coming up with a low budget underwater positioning system for when out scuba diving. Knowing that a GPS signal will never break much below the surface of the water, I was wondering if there were any alternatives that anybody has heard of. Just spitballing here, but since scuba divers are required to have a floating buoy flag tethered to themselves to alert boaters, I'm wondering if it would be possible to: (1) mount an Arduino with GPS shield above water on the buoy in a waterproof case and then (2) run some form of wire casing with low cost sensors that can measure "bend" / joint angle at fixed points along the tether wire down to the diver.
Of course, a very simple solution would be to just have a waterproof button wired alongside the tether and center the buoy overhead and "capture" the GPS point -- however, sometimes visibility doesn't permit that. I know there is addressable LED tape on the market that is fairly inexpensive in lengths up to 40-60' and that you can send info into, just was wondering if there might be some equivalent for getting joint angles sent back to an Arduino board.
Any ideas/thoughts/etc on this would be great! Thanks!
Before the days of GPS we used to use what was called a taut-wire system for maintaining position of our floating offshore oil platform. An anchor point was fixed to the seabed and a wire was kept under constant tension to the platform. The angle was measured between the anchor and the platform, plus a measure of water depth. From these a calculation was made of platform position relative to the anchor. OK an interesting story but of no use to a scuba diver.
One of the "normal" ways for doing underwater position sensing is to place at least three sonar transmitters at "known" reference positions on the seabed then triangulate your position on a receiver which measure time differences between signal arrival times. You could turn the whole idea upside down. Three fixed floating buoys each with a sonar transmitter. One the basis that the sea is level (not crashing waves) then you can triangulate your position from the time it takes signals to arrive. Note that all sonar transmitters will have to be synchronised so that they transmit at identical times.
Now I leave it to someone else to do the hard bits !!
@jackrae - That actually is great information to have for the taut-wire system. Do you think it would be possible to, instead, reverse the idea of the taut-wire system? For example, have the depth sensor down with the diver as well as a waterproof trigger and then pull the tether taut and somehow register the angle at which the tether goes into the water from the buoy. Relatively new to this area with the Arduino so I'm not sure if there is a type of "ball-joint" sensor that can register this type of information but it seems do-able. Thank you again for your input on this and let me know if you have any knowledge on that type of sensor! I'll continue to search online for one and post back here if I find one.
That buoy is achored or could you pull it towards your position?
If its achored you could just use some wire and a gyro/accelerometer and keep the wire/cable under some force.
With the buoy position, wire lenght(like those dog wires) and angle you could determine your position.
But the waves and the motion in the wire will add many problems for a measurement. Maby a second gyro just to caculate the waves
If your buoy is not anchored it will just move towards you. Maby you could pull the wire and wait untill the buoy is right above you and pull a trigger to save that position / wire lenght of the buoy.
But that could be pretty slow
But now you could also add like in the flying examples swimming ardboat-buoy´s that keep their position and measure like said above.
Underwater IR is absorbed really quick. Ultrasonic will irritate animals i read somewhere.
All other options i think require more than one transmitter/reciver or could irritate animals like electric fields from 2-3 buoy´s ...
There is a underwater navigation called tamin i found.. but seems expensive
Its not cheap, in fact its very expensive but we sometimes use USBL for tracking ROV's subsea, more details here:
In theory its just a subsea acoustic transceiver and transponder beacon so a homemade one could be made to operate over smaller distance the scuba diver will operate in.
