Almost 25% of world’s seafloor now mapped

Re:Almost 25% of world’s seafloor now mapped by walrus01 on Monday October 17, 2022 @06:19PM (#33240247)

military submarines do not as a matter of practice run around in general navigation pinging things, because that kind of defeats the purpose of hiding where you are

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Re:Almost 25% of world’s seafloor now mapped by jcampbell1 on Monday October 17, 2022 @06:52PM (#33240564)

The passive sonar from their own prop noise would easily show a mountain. There is a reason about 30 people were demoted due to the incident. Bottom line is they weren’t paying attention to their sonar.

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Re:Almost 25% of world’s seafloor now mapped by laverya on Monday October 17, 2022 @09:44PM (#33242009)

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.

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Re:Almost 25% of world’s seafloor now mapped by maxwindiff on Monday October 17, 2022 @11:05PM (#33242499)

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

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Re:Almost 25% of world’s seafloor now mapped by laverya on Tuesday October 18, 2022 @12:50AM (#33243095)

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?

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Re:Almost 25% of world’s seafloor now mapped by walrus01 on Tuesday October 18, 2022 @12:17AM (#33242918)

> 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.

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Re:Almost 25% of world’s seafloor now mapped by laverya on Tuesday October 18, 2022 @12:49AM (#33243089)

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

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Re:Almost 25% of world’s seafloor now mapped by morsch on Tuesday October 18, 2022 @01:35AM (#33243342)

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.

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Re:Almost 25% of world’s seafloor now mapped by laverya on Tuesday October 18, 2022 @10:40AM (#33247932)

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.

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Re:Almost 25% of world’s seafloor now mapped by CryptoBanker on Tuesday October 18, 2022 @11:50AM (#33249275)

The sound of the water rushing pass your bow would deafen any passive sonar arrays when operating at flank speed…

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