Electromagnetic Absorption in the Ocean

[RobbyQ]

The recent rescue operation of a sub in the ocean made me wonder how difficult it is to communicate with underwater vessels. Is it that all parts of the EM spectrum gets absorbed at extreme depths that things like GPS is not possible. I wondered what wavelengths of the spectrum were absorbed first eg at a certain depth all visible must be absorbed as the the sub is in complete darkness.

 

[Vanadium 50]

The attenuation length is proportional to wavelength - i.e. 1 wavelength down you are down a factor of x, two wavelengths down x² and so on. So you want to go to very low frequencies.

Unfortionately, the maximum data transmission rate is proportional to frequency. So the deeper you go, the less communication you have with the outside world.

GPS odes not work on submerged vessels. There are other navigation methods. (And people were able to suvvessfully navigate ships before GPS - honest!)

 

[RobbyQ]

GPS odes not work on submerged vessels. There are other navigation methods. (And people were able to suvvessfully navigate ships before GPS - honest!)

Thanks for the clarification. I was thinking more about GPS position being relayed to the outside world (not so much their own navigation) in terms of the rescuers being able to locate them. But I see this isn't possible from your information.

 

[Vanadium 50]

"Rescuing" a disabled submarine is more Hollywood than reality. It's happened a handful of times, like the USS Squalus. This was in the 30's and amazingly more than half the crew survived.

If this is about the Titanic submersible, the problem isn't that we don't know where it is. The problem is that we know where it is. It's in 2-1/2 miles of water. Now what do we do? Can you swim 2-1/2 miles? On one breath?

 

[RobbyQ]

"Rescuing" a disabled submarine is more Hollywood than reality. It's happened a handful of times, like the USS Squalus. This was in the 30's and amazingly more than half the crew survived.

If this is about the Titanic submersible, the problem isn't that we don't know where it is. The problem is that we know where it is. It's in 2-1/2 miles of water. Now what do we do? Can you swim 2-1/2 miles? On one breath?

Not suggesting anyone could swim to that depth or any Hollywood connotations. And it's not just the depth it's the area. Let's stick to the original question about locating it and EM degradation.

 

[berkeman]

Let's stick to the original question about locating it and EM degradation.

EM is useless underwater, so scanning sonar is the best bet for finding the lost sub. If there were an attack sub in the area, they could likely search the bottom with their scanning sonar, although I have no idea what kind of resolution they might have with that system. The Seawolf class subs would be able to go down to 490m max, so that's still a long way from the bottom. I also don't know how good their scanning sonar resolution is when looking way down below the sub like that.