gps

[Bruce3]

im not sure how depth effect gps signals but im thinking of sealing my gps reciever into one of those vac bags that heat seals the opening shut. i dont think operating the bottons would be a problem cause they're pretty big and spaced apart. has this been done before?

 

[laserdoc]

My hand held GPS has a hard time in the woods around the pine trees. It may not work so well at depth. I heard of someone taking a transponder and floating it at the surface but not so sure it really worked well. Try your idea and see if it works.

 

[Tamas]

Signal will not penetrate the water (rather "bounce" off the surface) so you will not have any signal underwater -- but feel free to try.

There are some DIY surface buoys that use a receiver on the surface and then have a line going down to the unit, but calculations for the line angle/tension/depth have to be made to get locations

 

[Bill51]

The best I've gotten in tests is to pick up a signal under 3-4" of water. Anything more and the signal won't penatrate.

 

[dbombtek]

Its a waste of time the signal is not strong enough to penetrate the water if you want to track your position then attach to your float like you would raise or lower a flag that way you can mark your position without a surface interval.

 

[herman]

Besides the fact it will not work under more than a few feet of water, the water pressure in more than a foot or 2 will press the bag against all the buttons at the same time and keep them pressed makng the gps useless even if the signal would get to it.

 

[H2Andy]

yeah, what everybody said

GPS doesn't work under water. Navy tried for years, and unless it's still super-top-secret, they didn't have any success

they use ship's inertial navigation system (SINS) which keeps track of their position relative to a fixed point.

then they come up to periscope depth and get a GPS loacation, calibrate the SINS, and away they go again.

 

[mirrocraft]

everyone here is correct even the navy has to send a unit to the surface for satelite com. and gps signal. its really hard to do things like that under water. what will disapate even a wireless signal thats under water with you very quickly. for example wireless under water comm. if you get more than a 10 or 15 ft away your more than likely not going to receive a signal.

 

[Flatliner]

Seems like there is an old post by someone with a handheld GPS in a clear waterproof container. Floats it up, drags it down and it shows the point it was when it lost signal. I have thought about seeing if I could use a thin antenna wire in my marker bouey when I am diving from shore.

 

[Flatliner]

In looking at my "ideas" file, I copied the original post:

"I'm the above-mentioned person using Magellan GPS underwater. (You may have seen my
recent article in Underwater Magazine). A free eBook is available at:
http://groups.msn.com/divergps *(a non-commericial site...nothing for sale).
I use one of 3 possible deploment methods, depending on depth and conditions. Lately, I've been "towing" a clear housing (Otterbox 9000) on the surface...the housing is only pulled below briefly to "mark" a point, or to gain awareness of the boat's position.
Here's the set up... The housing floats on the surface with an attached nose cone (to reduce drag)...this is followed (on the surface)--by about 25 ft. of bouyant poly-line....which is attached to a unique "no drag" dive flag. I simply tug lightly (to get the housing to move forward to the desired position)--then, pull down in a hand-over-hand position...gain data...drop the housing (which returns to the surface).
I've been using different variations of this method for about 6 years with good results.
As stated...the above-mentioned web site will provide further details, and further methods of deployment. *Be sure to see the photo section. **To answer a frequently asked question: It's often asked if this method allows the housing to drift to a distant point (rendering a mark innacurate)...not a problem, in this applicaton...it's where the housing is pulled below (losing signal) that matters. This is easily controlled by the diver. Most divers are not in the water enough to bother, but researchers and the most avid divers can have plenty of fun with this! You can test the basic theory on land: Take a Magellan gps and set up a land simulation. You simply cover the antenna with alluminum foil (to simulate periods of signal loss underwater). In real world applications (after significant periods of signal loss)...it takes about 60 seconds to get a fresh signal. However, in the above described surface-tow method, the wait is avoided, and data is available in mere seconds. Constant signal?---towed antenna??...that's fine if you want to go to the trouble, but I'm trying to use the most basic method possible."

Hope this helps
Robert