Underwater GPS

[Falcon99]

3-Dimentional positioning of the diver underwater using sonar trilateration seems like a great idea, but it is way too expensive for me. However, I am interested in sonar devices such as Neverlost, Eye Sea, and XIOS which provide bearings back to the boat. They are still expensive, but I have read some interesting threads that describe their operation. see: http://www.scubaboard.com/t26321.html If you keep the batteries charged and dry, they beat dead reckoning.
Chris

Ahh! Now you have something! You have solved the last variable. IF you can obtain a bearing (in either a boresight LOS, or Magnetic) from the "box" to the boat AND receive the boat's GPS position, AND obtain the point-point diver-boat distance (sonic transponder), you have everything you need. You can now provide the exact 3D position of the diver with surprizing accuracy. The unit has all the variables it needs to calculate the exact coordinates. It can now do anything a normal GPS can do as well - log position, times, depth, ect....

No need for differential here. Differential would be hard to do with the boat anyway. You don't know its exact position with better accuracy than GPS, so there will be no benefit. You could use a very similar method, but for the point-point calculations - as I said above, get an angle and the distance, everything else is elementary.

Most differential GPS systems are post-processed now anyway

You da man!

(It doesn't take much to get an Engineer like me excited - I work with Inertial and GPS stuff at my "normal" job

James

 

[Don Burke]

(It doesn't take much to get an Engineer like me excited - I work with Inertial and GPS stuff at my "normal" job

Here's a system that has some possibilities:

http://www.underwater-gps.com/3uwgps/ugps1.html

A master buoy and two slave buoys would seem to be all you'd need to form the net.

 

[Falcon99]

Here's a system that has some possibilities:

http://www.underwater-gps.com/3uwgps/ugps1.html

A master buoy and two slave buoys would seem to be all you'd need to form the net.

Yep. It looks like they use two bouys for a spherical solution to calculate the diver's range. I still think it can be done without a tether, though.

 

[darkmoon3d]

Whoops... Forgot to post the link!

Here it is -- http://www.plsm-instrumentation.com/

I found this site a while back. A bit pricy but and not sure if it uses gps or not; but it allows for underwater measurements and modeling very precisly.

Can't wait until this product becomes cheaper for consumer rather than profesional use...

 

[Helmet]

I get questions about underwater GPS all the time in classes. What anyone who uses GPS knows is that they aren't always accurate down to the foot. In fact, the satallites can be "detuned" during times of international conflict. Mariners often travel many miles and use GPS to get within 50 to a few hundred feet of a destination. Divers usually travel a few hundred feet max underwater. What good would a system be that was only accurate to a few hundred feet at any given time? A good ol' compass and proper navigation training and practice make totally adequate tools for getting to where you want to underwater. Having underwater GPS would be overkill. It would be like having GPS to go down to the basement of your house or to navigate around your backyard.

-Helmet

 

[archman]

In fact, the satallites can be "detuned" during times of international conflict.

I have been informed that such "detuning" is only implemented within GPS constellations over areas of conflict. Divers shouldn't be in such areas, needless to say.

As for accuracy, well if you have enough satellites in a non-obstructed sky, you should have errors limited to less than 20 feet. With WAAS implemented (and many nearshore dive areas in the U.S. are in range of this), you can pin that down to less than ten feet. I've used it quite a bit in the lower Keys to locate small reef features less than 15 feet across, and it's never let me down. I use a Garmin MkV.

 

[Don Burke]

I get questions about underwater GPS all the time in classes. What anyone who uses GPS knows is that they aren't always accurate down to the foot. In fact, the satallites can be "detuned" during times of international conflict. Mariners often travel many miles and use GPS to get within 50 to a few hundred feet of a destination. Divers usually travel a few hundred feet max underwater. What good would a system be that was only accurate to a few hundred feet at any given time? A good ol' compass and proper navigation training and practice make totally adequate tools for getting to where you want to underwater. Having underwater GPS would be overkill. It would be like having GPS to go down to the basement of your house or to navigate around your backyard.

-Helmet

If you take a GPS receiver around your back yard and record the raw positions and times, you can get precision corrections for those positions and know where every shrub in your yard is within a couple of feet.

Such a capability would be pretty handy for a reef survey, although I do see your point relating to wreck dives. The original question was related to shore dives in fairly shallow water and geo position would be a handy thing to know there since a diver can go quite a distance under those conditions.

 

[got4boyz]

WAAS is not available in all dive locations. So the accuracy of the system is probably about 50 ft 95% of the time.

In North America WAAS will be available at most dive sites. Afterall, when you are diving you are usually out in a big lake or the ocean so you have no obstructions to block the sattelites. With my external antenna I get WAAS inside my house and I'm not near any windows!!!

Helmet - You are a bit behind on the capabilities of GPS. Newer GPS units are WAAS capable now, which means they are typically accurate to 9 feet, 95% of the time. And in time it will only get better. Check out this link if you are interested in learning more about WAAS.

http://www.garmin.com/aboutGPS/waas.html

 

[Cabo31]

Submarines use Inertial navigation to navigate underwater. Thus at a certain point in time they know where they are, ie just before they submerge, then the Inertial navigation system is used until they surface again.

 

[Don Burke]

Submarines use Inertial navigation to navigate underwater. Thus at a certain point in time they know where they are, ie just before they submerge, then the Inertial navigation system is used until they surface again.

I've run those systems. They aren't the magic solution many would lead you to believe, especially in shallow water.