Thanks for this insight. I love how the SDMB has so many knowledgeable people, whereas I have little knowledge but lots of curiosity.
Yeah, you’ll find a million self-proclaimed “experts” online–I’ve found that SDMB is one of the few places where people bring receipts and are honest and forthcoming about the things they know and don’t know.
That’s the fundamental element here.
That and the awful puns.
We’d implode without them.
Maybe they have a timestamp for that moment in the video that they can compare to the time that the US Navy heard the implosion. If the times line up, they go with Occam’s Razor.
I would be curious to know if it is theoretically possible that the message from the sub was transmitted at a frequency that caused it to take a more circuitous route through the various layers of water. Because isn’t it correct that sound waves don’t necessarily take a straight path through water, particularly when traversing layers of varying temperature, pressure, and salinity? The thermocline and whatnot?
But then of course I’d wonder how, if the implosion really was so great that it could cause acoustic effects at the surface or on the mother ship’s hull that it didn’t also render any other kind of signal from the sub to the ship completely indiscernible. Because isn’t that a concern with sonar, too? That explosions and such can render it temporarily ineffective?
Unfortunately, it’s been a long time since I had to know about these things, and it was never my specialty, so I really am asking.
I can’t imagine they’d be able to get that precise, considering that the Navy sonar would have detected the sounds from hundreds (thousands?) of miles away and, as noted, the speed of sound varies in water with things like depth and salinity. Maybe they could get it on the range of a minute or at least minutes, but here we’re talking potentially milliseconds of precision needed to get a useful comparison.
As it happens, I work in a quasi-related field, analyzing subsea seismic signals, and we do a fair amount of water velocity analysis on a regular basis.
At any rate, the function is not exactly linear. I wouldn’t expect the velocity of sound in water to get too much above 1500m/s at depth. The pressure effect only goes so far.
It’s a bit cold up there in the north, but I’d still expect the fastest velocity near the surface (first ~100m) which, depending on the season could range from 1500 to 1550m/s (fastest in the summer, of course), hitting a minimum around 1480, give or take, at ~1000m depth, and then slowly increasing to about 1500, again give or take, and not getting too much above that. I shouldn’t think it hits 1530 unless there’s some local layer of warm or extremely saline water.
But at any rate, assuming a constant 1500m/s won’t be far off for most purposes.
I’ll preface this by saying that most of my hydroacoustics knowledge is from 25 years ago when I was an actual working sonarman so I can give you the Navy answer but I’m not a physicist.
Generally, no–the interaction of sound with layers is speed-dependent and not frequency-dependent. I want to say there might be some small frequency dependency in refraction, but it’s insignificant enough to be ignored. (And definitely insignificant at tiny ranges like these.)
Yeah, explosions can cause a lot of reverb in the water that elevates the noise floor and might impact performance for a bit… but it’s generally pretty short-lived and doesn’t cause many problems with most modern systems. (Obviously though–nothing was coming from Titan after the implosion anyway.)
Ah, great! I was hoping someone would check my work haha.
Like I mentioned above, it’s been years since I’ve had to deal with most of that stuff. My work is all between the hydrophone and glass now–so I’ll admit I’m a bit rusty.
Great discussion here. I’m expecting that documentary on Wednesday to be really good.
Can confirm. Unless there’s some ridiculous heterogeneity in salinity in the water column, there should not be any frequency dependent velocity effects, and it should primarily be temperature/salinity related, which will mainly be a function of depth. Note, this is not true once you hit the dirt under the water. There’s plenty of frequency dependence in sound velocity once you get to rocks.
There are thermoclines that can act as waveguides but usually not in a frequency discriminatory way.
This is basically how oil and gas companies search in the ocean. Instead of submersibles, they set off compressed air guns (dynamite, often used above water, is contra-indicated), and those things are designed to be detected by recording nodes set on the ocean floor. So, we have reverse this situation (the impulsive source was at the bottom and they were listening up top) and usually shallower depths (1-2km rather than 3km depth) but nothing fundamentally different in an acoustic sense. And to determine the nature of the subsurface, getting that sort of thing right is critically important or else they’d drill a lot of dry (and ridiculously expensive) wells.
And the submersible set off a larger bang than that, so the idea of a detecting an impulsive signal at that distance is among the least surprising things I’ve read.
ETA: The idea of one sound “overtaking” the other is bunkum, though. I can buy some kind of computer processing delay but not the idea that one acoustic signal traveled faster than another in sea water. That doesn’t make a lot of sense.
That said, I’m not going to comment on the “what was that?” There’s a lot of questions about what exactly they heard and when, and the quality of science reporting in general is poor. I also hope for clarity out of the doc.
Could it be herring?
I have nothing to contribute to this discussion, other than that fabulous story from the 90s and some darkish humour.
So you’re saying that, when it comes to the distance the sound of the implosion had to travel to get to the surface, they could have cut it down with… a herring?
The background noise was very faint so I turned the volume way up, and when the implosion came I jumped in my chair. The implosion and the reverb sounded like large bombs. The violence that tore that thing apart must have been incredible.
They could have, but the engineers declared that they would do no such thing!
I wouldn’t be so sure. You know how loud a kettle can get just before it boils? That is the sound of microscopic bubbles collapsing. I can easily imagine that the implosion, essentially the collapse of an extremely large bubble, would be unimaginably loud.
Of course, this is proctology conjecture. So take from it what you will.
Heh, you’d be surprised at the number of things we’ve heard in the ocean that we couldn’t determine the origin of for literal decades.
The Minke Whale probably has to be my favorite:
After a two-hour Twitter outage earlier this week, Elon Musk announced that he was going to be spending more time on his companies, including Twitter and SpaceX.
Regarding the Twitter outage, Musk said “The failover redundancy should have worked, but did not.”
I think that was what Stockton Rush was starting to say when the Titan implosion occurred.
It showed here last night.
(Doesn’t really add much tbh.)