GPS underwater

In the case of snow this is due both to the small particle size and to
the fact that the water is frozen. In the experiment I described before
in this thread, a layer of water only a few millimeters thick stopped
reception of the GPS signals. Placing the same plastic lid filled with
water in the freezer and then repeating the experiment with a layer of
ice instead of liquid water showed very little reduction in signal
strength (actually SNR). When bound in a solid, the water molecules
are not as free to rotate and absorb energy from the EM field.

 

Garmin GPS 12 WILL work underwater. Its a matter of execution. put the gps
in a water tight seal casing ala underwater camera case. have an external
connection (water-proof type) for antenna. ensure the antenna is out of
water. and voila! gps works underwater.

 

Having the antenna out of the water has been discussed previously.