Can GPS work underwater?

[Born2bwire]

Originally posted by: dmcowen674
There is a system that tranlates GPS underwater but it is top secret technology.

 

[CycloWizard]

Originally posted by: Born2bwire

Not sure how he got in here, but I'm hoping it was a one-time thing.

 

[RESmonkey]

Isn't there a way to get GPS itself underwater? Like, refracted waves could be translated back and forth? Or is GPS not even EM, but the other wave form (longitudinal?)?

 

[Born2bwire]

Originally posted by: RESmonkey
Isn't there a way to get GPS itself underwater? Like, refracted waves could be translated back and forth? Or is GPS not even EM, but the other wave form (longitudinal?)?

The conductivity of water kills off the GPS signal on the order of inches to feet. Even soil is conductive enough to make GPS unusable underground. I've worked on subsurface navigation systems and GPS is way too high of a frequency to expect it to penetrate a conductive medium.

 

[lawton3920]

mark 19 an mark 23 gyro-compasses.

 

[SilthDraeth]

if it means anything the gps on my phone poops out in the Chesapeake Bay tunnel

You poor soul. How long have you been trapped in there?

 

[Lemon law]

The way I analyze the problem, regardless if the high tech sub is one of ours or the enemy, a boomer or a sub hunter, being undetectable is job one. Which means traveling super slow to avoid making no prop noise is totally vital. Because low frequency sounds propagate super well underwater in ranges well over a thousand miles. While high frequency GPS signals are unlikely to penetrate more than a few feet of water.

So suppose such a sub has to communicate with home base, its still an easy to solve problem. Just release a 99% the density of water radio transmitter and let it float noiselessly to the surface. Give the sub adequate time to get away. As the drone suddenly transmits a coded message lasting only milliseconds to home base, and then transmit its reply at low frequency through the water, back to the sub. Sure everyone and their brother in law may know where the drone is, as for the sub, it may be 200 miles away by then. As for the drone, once the received message is transmitted, it lets out its retained air, and sinks to the ocean bottom.

Just my theory of how to solve the problem, if a pea brain like me can think of that solution, chances are smarter people figured it out years before. Which is not to say its the only way to skin that cat.

 

[herm0016]

Once upon a time, they wanted to build a submarine antenna in the UP of Michigan. It was for 18KHz. It was soethin glike 50 miles in length.

It was at least delayed for a while beause they were afraid it'd make the cows sterile, but I believe it was ultimately built (~15-20 years ago).

ULF / LF can penatrate the Earth and the oceans. However, the data rate is so small, they are restricted to small letter groups that are coded for specific actions (like 'AA' = "Surface RFN and get a real important message via UHF / SAT")

FWIW

Scott

http://www.hep.wisc.edu/~prepost/ELF.pdf

its there. I have seen the gate. if you have some google fu you can pull it up on the sat images.

east of republic near long lake.

 

[Modelworks]

GPS has already been discussed as not working beyond a couple feet at best, subs have buoys for that. The military did use ELF for communication which is really low about 80hz, it was possible to send a signal in the USA and receive it thousands of miles away because the waves themselves are 2000 miles + long, the reason for the closure of the programs is because of the amount of power it takes and the complicated antenna setups, antennas were several miles long , then you also needed lots of power to send a single message, think 10-20KW for a single transmission because you couldn't build an antenna to match the frequency, it would be an antenna almost 1000 miles long.

 

[Mark R]

GPS is radio waves at 1.6 GHz. Water (or any conductive material - including concrete, rock, soil, etc.) will result in very severe attenuation of the signal within a few centimeters.

As it is, GPS signals are preposterously weak at the earth's surface - around about 1000-10000 times weaker than the signal strength that will cause a cell phone to lose service.

The GPS timing pulses repeat 1000 times per second - but the receiver will often need to take 10000 averages or more, just to be able to pick it out above the background noise. Once you've got the signal and know when to expect the next pulse, finding it is a bit easier, and can usually be done with only a few hundred averages.

 

[maciekish]

How do submarines navigate?

I always thought they used GPS, though I could definitely be wrong.

Sorry to get slightly off topic OP

They use INS just like airplanes on translatlantic routes before GPS was invented. It uses high precision accelerometers and gyroscopes to integrate all changes in speed and direction to calculate a position.

 

[pitz]

The system that the military uses to communicate with submerged submarines is called "TACAMO". It basically uses an antenna a few miles long strung from either a E-6B or an E-4B aircraft (modified Boeing 707 and B747s respectively). Because its very low frequency, the symbol rate is extremely low. But its high enough to transmit very cryptic coded Emergency Action Messages to the submarines (which would presumably contain the balance of the cryptographic keys necessary for a Trident launch).

Basically the antenna needs to be held vertical or near vertical, so that means that the E-6B/E-4B aircraft has to fly a very tight bank angle, sometimes for hours. Talk about vomit-inducing, to be flying 360's in the sky literally for hours. The aircraft's auto-pilots apparently have been retrofitted with logic that automates this process.

As others have pointed out, GPS is easily attenuated by submersion, and inertial navigation is used in its place, with eventual updates from GPS and/or stellar (star-sighting) navigation.

Actual SLBM's launched from nuclear submarines carry out a manoeuvre in their post-boost phase where an optical camera comes into view of the stars, and software is used to calculate a precise navigational fix prior to final manoeuvres and separation of the (multiple independently-targetable) re-entry vehicles.

 

[John Connor]

How many time is INS going to be mentioned? INS isn't used exclusively in transatlantic, transpacific crossings. It's used all the time in aircraft. For example, the 737 has two gyros and a GPS.

DARPA is working on a miniature INS for augmentation. http://www.darpa.mil/Our_Work/MTO/Programs/Micro-Technology_for_Positioning,_Navigation_and_Timing_%28Micro-PNT%29.aspx

 

[dkozloski]

Solid state Ring Laser Gyro INS systems the size of a hockey puck are used to track the cars and stabilize GPS tracking in a Sprint Cup race and their positions are reported to internet watchers using the RaceView tool on the NASCAR web site. Pure GPS won't do the job because the satellite signals are heavily attenuated by the catch fences at the tracks. Early ballistic missile submarine INS systems were the size of a garbage can. Current systems with an order of magnitude better accuracy will fit in your pocket.

 

[pcgeek11]

SINS ( Ships Inertial Navigation System ) Navigation and MARDAN Computers were used on the old FBM Submarines for navigation and to give the missiles the navigation data up to the moment of launch.

http://www.ion.org/museum/item_view.cfm?cid=2&scid=4&iid=4

http://www.tendertale.com/tttj/tttj2-5.html

 

[sonitravel09]

AS an alternative you could use sound waves - obviously not from a satellite - which could create a triangulation system. We read that whale song can run hundreds of miles - presumable an artifical analogue could be created. Not sure why one would want to though - and it might further confuse the whales and dolphins who already have to put up with terrible sound pollution.

 

[SOFTengCOMPelec]

I was going to post my own answer, but my source link seems easily good enough.

Source

If you read How GPS Receivers Work, you realize that GPS signals are fairly weak. They are coming from satellites orbiting at 11,000 miles. By the time the signals get to earth, they are so weak that even heavy tree foliage can block them.
Therefore, the only way for a submarine to use GPS signals is to come to the surface or to tow a buoy that is floating on the surface. There is no way for GPS signals to penetrate the water.
So how do submarines navigate when they are underwater? The most important tool is the inertial navigation system. An INS uses precise accelerometers and gyroscopes to keep track of every change in the submarine’s speed and direction. A computer monitors all the changes and therefore knows where the submarine is. Obviously over time small errors add up, so the submarine will come to the surface periodically to get a GPS reading and recalibrate the system from a known point.

 

[dkozloski]

AS an alternative you could use sound waves - obviously not from a satellite - which could create a triangulation system. We read that whale song can run hundreds of miles - presumable an artifical analogue could be created. Not sure why one would want to though - and it might further confuse the whales and dolphins who already have to put up with terrible sound pollution.

Directional oil drilling uses "mud thumping" with the drilling mud that is pumped down the drill hole to communicate with the drill bit to determine bit location and direction of travel and to send steering info.