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Passive sonar shows "things making noise". It doesn't show things that do not make noise. Mountains do not, as a general rule, make noise, and do not show up o

Passive sonar shows "things making noise". It doesn't show things that do not make noise. Mountains do not, as a general rule, make noise, and do not show up on passive sonar. In addition, when running at flank speed the efficiency of passive sonar is greatly degraded by flow and machinery noises. The way a submarine avoids running into seamounts is a combination of very good maps, very good dead reckoning, (IIRC) gravitational anomaly detection (tied to more great maps), and if all else fails high-frequency (short-range) active sonar. It's a really interesting system! But I don't think passive sonar ties into it.

maxwindiff 4y ago
I'm curious why this reply got downvoted so much. Can someone explain if the content is correct or not and why?
- laverya 4y ago
  I've got no clue about the downvotes either. Maybe because the first version of the comment was a little snarky, and didn't include how submarines actually avoid crashing into things?
walrus01 4y ago
> very good maps, very good dead reckoning There's a whole series of highly classified inertial navigation units used in aviation and submarine applications. The ones for use above the ocean's surface have many DoD applications in a theoretical GPS-jammed environment in warfare against an equal-tech adversary.
- laverya 4y ago
  Yeah, I should have said "very good inertial measurement systems" instead of dead reckoning. It doesn't leave quite the same impression!
morsch 4y ago
Mountains do make noise when they reflect the sound your prop makes. I took the gp to refer to that. Whether you can use that for collision avoidance, no idea.
- laverya 4y ago
  There's a few problems with this. For one, your prop noise is going to be almost entirely masked directly ahead of you, because there's a whole submarine in the way. Isolating "sound of our propellers from in front of us" from "our propellers behind us" is certain to be extremely difficult if it's not completely impossible too. I've got no idea where jcampbell pulled their information from, but I've never seen anything to even suggest it's possible to use your own prop and machinery noises like that.

maxwindiff 4y ago

I'm curious why this reply got downvoted so much. Can someone explain if the content is correct or not and why?

laverya 4y ago
I've got no clue about the downvotes either. Maybe because the first version of the comment was a little snarky, and didn't include how submarines actually avoid crashing into things?

walrus01 4y ago

> very good maps, very good dead reckoning There's a whole series of highly classified inertial navigation units used in aviation and submarine applications. The ones for use above the ocean's surface have many DoD applications in a theoretical GPS-jammed environment in warfare against an equal-tech adversary.

laverya 4y ago
Yeah, I should have said "very good inertial measurement systems" instead of dead reckoning. It doesn't leave quite the same impression!

morsch 4y ago

Mountains do make noise when they reflect the sound your prop makes. I took the gp to refer to that. Whether you can use that for collision avoidance, no idea.

laverya 4y ago
There's a few problems with this. For one, your prop noise is going to be almost entirely masked directly ahead of you, because there's a whole submarine in the way. Isolating "sound of our propellers from in front of us" from "our propellers behind us" is certain to be extremely difficult if it's not completely impossible too. I've got no idea where jcampbell pulled their information from, but I've never seen anything to even suggest it's possible to use your own prop and machinery noises like that.