a reply to: DigginFoTroof
The biggest question which I don't recall seeing in your project is fresh or salt water? If you know how to read engineering graphs, this picture is
worth a thousand words by showing two different curves for how much electromagnetic signal is lost per meter in salt water (top line) versus a
specific body of fresh water (bottom line).
The GPS frequencies are off the right hand side of the chart, like way off the chart. So GPS signals don't do well underwater, and even the lower
frequency example shown of 1.8 MHz doesn't fare will in seawater.
What the chart shows is that lower frequencies fare better, but some of these frequencies may not be readily available for a number of reasons. Even
if you could use those frequencies, the other problem you could run into is that lower frequencies can't carry as much information so to use them in
some kind of homemade GPS might mean getting very low quality signals that won't give much accuracy.
If you can get a fix on your original position at the surface using regular GPS, you should be interested in how other subs navigate without using any
underwater GPS, they use a inertial navigation systems which incorporate a gyroscope, accelerometer, and a computer. RLGN is replacing ESGN.
"ESGN (Electrostatic Gyroscopic Navigation)
operates in a near perfect vacuum
rotor is solely supported by an electrostatic field
resets only required once every 30 days
Wearing out and failures are increasing, so being replaced by RLGN
RLGN (Ring Laser Gyroscopic Navigation)
Operates without moving parts
Two (or more) lasers travel around object
As ship moves, laser takes slightly more time to travel
Time delay causes a phase difference that is used to calculate movement"
I have no idea how much they cost, but they don't sound cheap.
If there are features on the bottom, and the sub can ping those, it can navigate by those features but it's not too accurate.
edit on 20181224 by Arbitrageur because: clarification