Sound travels hundreds of miles under water

[Saboburns]

Sound travels hundreds of miles under water. Actually, I believe sound travels thousands of miles underwater. I am no expert on this matter, but have read that submarines, during the cold war, picked up underwater signals from hundreds of miles away. That the real trick to underwater SigInt is not getting the right signal, but is eliminating all the clutter from thousands of other underwater signals.

So what I'm getting at is, how it takes so long too get these pings in deep ocean water? I just think that military expertise in this matter would make picking up a pinging object under water is not that difficult.

But apparently it is.

What am I missing?

[lumberjack_jeff]

1. It can travel long distances... within a thermocline.

If a hydrophone detects a sound at a given depth, the source of that sound is within that thermal layer. In practice this means "at approximately this depth, in this body of water" You won't hear sounds deep in the south china sea in the deep Indian ocean because of the intervening shallow water.

Since the black box is on the bottom somewhere, and you know at what depth the sound was detected, you should be able to narrow the search by concentrating efforts on places where the seafloor is at approximately that depth.

[Submariner]

2. Ships passing the Rock of Gibraltar could be detected

by submarine sonar in the Bahamas. In the 60s the sub I was on, a WWII era diesel-electric boat, could pick up ship traffic going into or out of the Med when ships passed the Rock. I suspect the sonar is even more sensitive now.

[SidDithers]

3. Depends on the frequency...

very low frequency sounds will travel farther than high frequency sounds.

But the ocean is a very, very big place.

Sid

[Motown_Johnny]

4. In addition to the above posts...

I would like to suggest that the position of the source of the sound at the ocean's bottom has an effect.


The topography of the sea bed could obstruct the sound. Essentially like trying to listen through a wall.

Along with the problems mentioned earlier with thermal layers, the sound can be blocked in all directions and you would need to get close enough to avoid the obstructions.

[Glassunion]

5. In the case of a black box within two miles

IIRC a black box ping can be heard up to about two miles. It sends out what I'd describe as a click.