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In 2009, Two Nuclear Submarines Collided Under the Sea (2016)

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Re: In 2009, Two Nuclear Submarines Collided Under the Sea (2016)

#71

Post by trhway »

baobabKoodaa wrote: post #6

So the submarines can't use active sonar, because their number one priority is to avoid detection... but then these subs are all parked in the same "parking spots" in the ocean. If the favored parking spots for submarines are so rare and small that collisions happen more than once, surely that undermines their stated number one priority of remaining hidden? If someone wanted to locate enemy submarines, surely they co…

USSR concept of naval bastions

https://en.wikipedia.org/wiki/Bastion_(naval)

>If someone wanted to locate enemy submarines, surely they could just send a bunch of underwater drones to swim through these parking spots?

back then it were US attack submarines which USSR tried to actively track and push out of the bastions.

Re: In 2009, Two Nuclear Submarines Collided Under the Sea (2016)

#72

Post by lnwlebjel »

uga4012 wrote: post #3

Are they really not detectable from space?

Not sure if they are, but I do know that the US Navy funded a lot of oceanographic research into predicting and understanding bioluminescence of marine organisms for this very reason. The surface waters of the North Atlantic have massive spring blooms of phytoplankton, which are sometimes bioluminescent, and could certainly give away the presence of a large subsurface vessel, possibly from space.

Re: In 2009, Two Nuclear Submarines Collided Under the Sea (2016)

#73

Post by Galxeagle »

One really fascinating aspect of sonar that leads to risks/collisions like this, is that there are ‘blind spots’ in the ocean. Because sound waves pass differently through water of different temperature and salinity and both of those change on gradients in the ocean, there are mathematical solutions to where a sub would be totally undetectable given a ship’s position and radar frequency. Because these locations are obviously useful for subs, two+ can sometimes end up in the same warm pocket, which obviously increases collision chances from a naive hundred-cubed-km search space

https://m.youtube.com/watch?v=AqqaYs7LjlM

Re: In 2009, Two Nuclear Submarines Collided Under the Sea (2016)

#74

Post by sealeck »

nradov wrote: post #30
baobabKoodaa wrote: post #6

So the submarines can't use active sonar, because their number one priority is to avoid detection... but then these subs are all parked in the same "parking spots" in the ocean. If the favored parking spots for submarines are so rare and small that collisions happen more than once, surely that undermines their stated number one priority of remaining hidden? If someone wanted to locate enemy submarines, surely they co…

There are no parking spots. Ballistic missile submarines conducting deterrence patrols are assigned to large areas covering hundreds of square nautical miles. The sub then maneuvers inside that patrol area to remain as hidden as possible. They almost never stop as it's easier to maintain depth control with at least a few knots of steerageway. So a collision in open ocean is theoretically possible but highly unlikely.…

Royal Navy subs have been known to surface directly underneath sailing boats in the Firth of Clyde (in Scotland).

Re: In 2009, Two Nuclear Submarines Collided Under the Sea (2016)

#75

Post by kragen »

omni wrote: post #25
earthbee wrote: post #14

Earlier quoted context omitted.

Then you could hear them coming and avoid them

If you can hear them, they've already found you

The path loss for active sonar is, logarithmically, twice the path loss for passive sonar. If the signal is 0 dB at 1 meter, it will be -40 dB at 10 km away (barring SOFAR, a regions these submarines probably try to avoid, and ignoring the reflections off the surface and seafloor), and the reflection (assuming an isotropic reflector) will be -80 dB. At 100 km, it's -50 dB and -100 dB.

So, if both sides can detect a -50 dB signal, the passive-sonar target will be able to detect the active-sonar probe 100 km away, while the active-sonar target will be able to detect the reflection from the passive-sonar reflector 0.316 km away. Or maybe 0.315. And that's assuming perfect discrimination.

(By transmitting a signal you can barely detect, you can reduce this discrepancy: if you reduce the signal amplitude by 30 dB at 1 m in this example, the probe can detect the target at 10 m, or maybe 11 m, but the target can't detect it until they're within 100 m.)

However, this massive advantage for passive sonar only really true if it's just as easy for the target to recognize the signal as it is for the probe. In fact, the probe has a huge advantage: it knows what the signal was. If it's just an ordinary chirp, this is of no help, because that's easy to recognize, unless you confuse it for a humpback whale song or something. But if it's Gaussian white noise, it's impossible for a single hydrophone to distinguish from the background noise of the ocean, except by amplitude. Advantage: probe.

But that's a single hydrophone. In fact, though, a point source of white noise is the easiest thing for a phased-array beamforming passive-sonar system to localize. The Triomphant is 138 m long, so if you stuck hydrophones all along its length, you could detect directional sources of sound with an angular precision of about λ/d, the one-dimensional Airy limit. The λ for your active sonar needs to be chosen to be small with respect to the targets you're looking at so it doesn't just diffract around them, so this is probably on the order of 0.1 radians, about 5 degrees.

Two can play that game, though, or thousands. The network of tiny drones can form a single ocean-sized phased array by squirting data back and forth over short-range ultrasound or laser links.

But guess who already has ocean-sized phased arrays of hydrophones for passive sonar?

sca4 posted this very worthwhile link, which talks a bit more about the scene: https://www.aspistrategist.org.au/prospects-for-game-changer...

Re: In 2009, Two Nuclear Submarines Collided Under the Sea (2016)

#76

Post by kragen »

idoh wrote: post #38
zoomablemind wrote: post #34

Earlier quoted context omitted.

> ...They're basically swimming blind. It did appear just like that. Shouldn't there be some proximity sensors to avert collisions with massive bodies? After all in the aftermath both subs were rendered mission incapable.

How would the proximity sensors work? The can’t go active sonar…

Ultrasound, magnetic, eddy-current metal detection, conductivity detection by conducting current through water, red light, VNIR, antineutrino detectors...

Re: In 2009, Two Nuclear Submarines Collided Under the Sea (2016)

#77

Post by kragen »

cryptonector wrote: post #62
jaywalk wrote: post #4

Earlier quoted context omitted.

Why do you think they would be detectable from space? That doesn't make any sense.

These subs are large, metallic, full of electric equipment, and heavy . They have magnetic and gravitational effects on their surroundings. They also have electromagnets to help hide their magnetic signatures. A network of very sensitive satelites with very precise clocks could be used to detect gravitational anomalies -- maybe, I'm not sure what kind of precision would be needed, or if that is achievable.

They're the same density as the water they're floating in, even though they contain some metal that is much denser.

Re: In 2009, Two Nuclear Submarines Collided Under the Sea (2016)

#78

Post by [deleted] »

daveslash wrote: post #70

Re >> "the French Ministry of Defense reported that the submarine had suffered a collision with an “an immersed object (probably a container).”" and Re >> "At some point, the two navies compared notes" I get that ballistic submarines want to stay secret and use passive sonar, instead of active sonar. But I also would have thought - if a submarine mysteriously ran into something under water that they did not expect to…

[deleted]

Re: In 2009, Two Nuclear Submarines Collided Under the Sea (2016)

#79

Post by traeregan »

bambax wrote: post #35
sca4 wrote: post #28

Earlier quoted context omitted.

Lot of dismissive reactions to these questions, but there actually are non sound related signals we use to detect submarines and there is absolutely research on how to do that from space. This article is great, but just read the "Signal Processing" section if you're interested in space. https://www.aspistrategist.org.au/prospects-for-game-changer...

Interesting article. Also, we are now able to reconstruct a conversation by analyzing the movement of the glass on a window to the room where people are talking. It doesn't seem absolutely out of reach that we could some day detect huge underwater vessels from analyzing surface perturbations.

> reconstruct a conversation by analyzing the movement of the glass on a window to the room where people are talking

May I please have a link to more information? I wasn't able to find anything, and this is very interesting.

Re: In 2009, Two Nuclear Submarines Collided Under the Sea (2016)

#80

Post by puglr »

traeregan wrote: post #79
bambax wrote: post #35

Earlier quoted context omitted.

Interesting article. Also, we are now able to reconstruct a conversation by analyzing the movement of the glass on a window to the room where people are talking. It doesn't seem absolutely out of reach that we could some day detect huge underwater vessels from analyzing surface perturbations.

> reconstruct a conversation by analyzing the movement of the glass on a window to the room where people are talking May I please have a link to more information? I wasn't able to find anything, and this is very interesting.

"reconstruct conversation glass vibration" brings up a lot of relevant results from a 2014 story from MIT. Sounds like it works in principle with any medium that can have its visible vibrations monitored (bag of chips is the main example, but they talk about other options such as plants or a glass of water).
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