How far does sound travel in the ocean? | Hacker News Reader

How far does sound travel in the ocean?

oceanservice.noaa.gov

57 pointspanabee47 comments

I think a more approachable resource on (a superficial but fundamental level) is Smarter Every Day's SONAR episode. He discusses and illustrates the complexities involved in sound, how it doesn't even travel in a predetermined path, and the variables involved in its distance/trajectory: https://www.youtube.com/watch?v=AqqaYs7LjlM

That whole series is really good, life on a submarine is so interesting

I spent two and a half years on one.

No it is not.

Just because you're over being in a submerged tube doesn't mean other people can't find it fascinating. I find the silent service totally fascinating, and would happily buy you beers to hear stories you are not allowed to tell.

Well how about I tell you the stories I can tell, for free?

I have to go get a car battery replaced, but when I come back, I'll share a few tales.

Sometimes, I would stare into the Reactor Compartment through the glass (there's a large-ish - around 6" - 8" if I recall correctly) porthole that allows you to look right into the reactor compartment at the nuclear reactor. I never stared for long... maybe 5-10 seconds at most, but staring at nuclear fission occurring is truly an awesome experience.

There's no Cherenkov radiation emitted, so you're just staring through glass at a bunch of metal, but you still know its occurring... and that was enough for me.

I think it is like a lot of unusual things. Looks fascinating from the outside, but it gets really boring really quick.

Everything military is a good example. Who doesn't like the idea of working on secret, state of the art technology? Truth is, the secret part mostly gets in the way, because of the "right to know", you don't really know what you are working on, and you may not even have internet access on your computer. As for the "state of the art", it tends to be pretty underwhelming. Besides military-specific constraints like stealth, it tends to lag behind civilian technology, probably related to the already mentioned secrecy that gets in the way.

Same thing happen when you get to work with really expensive equipment. Sounds great because who doesn't want a machine almost no one can afford? In reality, you are unlikely to get to play with it. Because it is an expensive machine, your company is going to make sure it is used to make money and not just for your own curiosity. Personal use is likely to get you fired.

> I spent two and a half years on [a submarine].

Hah! I spent a week aboard a fast attack, on TAD just before nuclear power school; the experience gradually convinced me that I should be a surface nuke. (My tuber buddies at nuke school joked that by making the switch, I raised the average IQ in both communities.)

That sounds like a submariner's joke alright.

I used to hear that "Navy nuclear submarine personnel are the top 10% of the Navy!" They would repeat that shit over and over to us at Sub School. After a year onboard the USS Honolulu, I remember thinking, "If this is the top 10%, I'd fuckin' hate to see the bottom 90..."

I did end up spending some time with the bottom 90%, briefly. After the Hono, I was transferred to Patrol Coastal Crew Charlie. At the time we were still attached to SOCOM, so it was a really great, if hard, life. The last 6 months or so of my time in the Navy, we got folded into "Big Navy". Not fun. At the time, each crew simply flew to an available PC boat, usually to relieve another crew, as 3 PC crews generally operated out of Bahrain and Kuwait at any given time. It was cheaper to ferry most of the PC boats over by large ship instead of trying to sail them, as you generally need to refuel a PC boat every 7 days, give or take.

Having to actually do maintenance on our equipment instead of spending hours every week at the range shooting and hours at sea practicing on the twin-50s and the 25mm autocannon was a real drag. I'm glad I got out when I did. It was all of the fun with none of the work, and then become all of the work and 5% of the fun.

I spent 6 years in the Navy, 4 of those on a fast attack. I would say that it was an exercise in the extremes. There were times of extreme boredom and extreme stress. I leaned a ton of interesting things. The crash course in real world systems and how they work together is something that I'm not sure I could have gotten in any other environment. But on the other hand, I easily cleaned more than I have in the rest of my life.

Another interesting thing, is to see how people react in these situations. Some people can't take the high stress, some the long hours, some the long stretches of boredom. And they deal with it in different ways. And it can bring out the best and worst in people. And everyone comes out of the experience changed.

Spent 3 years on a fast attack sub and can attest that though difficult and frustrating at times, life on a sub is indeed interesting.

One of my favorite tools onboard was our sound speed profiling software. While it was often wildly inaccurate compared to what we were "seeing" in sonar in real-time, it was fascinating trying to predict what we would and would not hear.

We definitely picked up MODUs (Mobile Offshore Drilling Units) form thousands of km away.

Also, there are many older submarines still out at sea, and many of them don't use sound dampening tech (i.e. rubber grommets) on their noisy gear (pumps). Pretty loud too.

I worked briefly in this field. The key concept is the “sonar equation,” but it needs to be modified to include the factors of the specific area of ocean (depth, cylindrical/spherical propagation characteristics, temp, shipping traffic, etc). There are not a lot of public sources on the topic, but here’s one I found, if you want a starting point to learn more: https://fas.org/man/dod-101/navy/docs/fun/part08.htm

What a crappy article. Apparently the answer is "it depends" but they're pretty sure it is "many kilometers".

> In fact, hydrophones, or underwater microphones, if placed at the proper depth, can pick up whale songs and manmade noises from many kilometers away.

This seems like a contradiction, but it isn't. Sound attenuation in sea water is extremely dependent on frequency. It is roughly a power law. Very low frequencies can easily travel extreme distances (0.001dB/km for 0.1Hz or so), but higher frequencies are attenuated more drastically. Whale song and man made noises have much higher frequencies. A quick Google search claims whale songs are around 80Hz to 4kHz. Absorption is around the 10 to 100dB/km range for 100Hz to 1kHz. So both statements in the article are true.

Disagree! The article explains something extremely cool: that there’s a layer in the ocean that acts like a megaphone, where sound that passes into it gets caught and propagates way further. That’s cool and specific.

Megaphones Amplify sound. Your analogy doesnt work. In no layer of the ocean is sound amplified.

Electric megaphones amplify sound. Acoustic megaphones direct sounds, much like what the article describes.

Yeah, I was thinking about the old fashioned cheerleading things, without any electricity involved. I even thought about being explicit in case someone was going to be pedantic ... there’s even an emoji for it

An example would have been nice. It's old technology now, but here's an example of listening across the Atlantic.

https://en.m.wikipedia.org/wiki/SOSUS

https://youtu.be/R462zEQ6RQA

It depends is the real answer for any things. Understanding what it depends on is an important part of the discussion. Most people have no understanding of sound in the ocean. There is a ton of information at: https://dosits.org - Discovery of Sound in the Sea.

-Full disclosure, I am affiliated with that website.

The article doesn't actually answer the question. How many kilometers and what is the depth of the sound channel? Where does the pressure/temperaure ratio cause sound to difract?

After reading such an article I feel none the wiser, as the words are barely defined and no specifics given. Is there anywhere else to find better info?

IIRC, "Principles of Underwater Sound" by Robert Urick [0] is considered pretty good.

A textbook that's helpful for actually implementing ocean acoustics models is "Computational Ocean Acoustics" by Jensen et al [1].

[0] https://www.amazon.com/Principles-Underwater-Sound-Robert-Ur...

[1] https://www.amazon.com/Computational-Acoustics-Modern-Signal...

Thank you for these. The First [0] link looks particularly interesting.

Blue Whale is the world largest (30m/100ft) and also the second loudest (189 underwater dB) animal, has been reported to communicate for about 1600 miles or 2600 km away. This distance is approximately the distance of Puerto Rico to the shores of Newfoundland [1]. The loudest animal goes to Sperm Whale with 230 underwater dB, and it's louder than the sound of jet engine at take-off. According to experts, whale's consciousness and sense of self is based on sound, not sight.

They communicate using sound types namely repeated songs (each song quantum duration of 15-20 seconds) and D calls (down-swept short pulse) [2].

I think that the longer repeated songs are for communication while the short D calls are for echo-location for determining sea depth, icebergs, islands and troupe of shrimps (their staple foods). The latter is similar to the mechanism being used by bats or blind human [3].

[1]http://news.bbc.co.uk/2/hi/science/nature/4297531.stm

[2]https://dosits.org/galleries/audio-gallery/marine-mammals/ba...

[3]https://www.youtube.com/watch?v=lAtVOK04XvA

Not sure how it's nowadays, however during the cold war, those serving in Soviet submarines often wore slippers to avoid making any loud noises so their counterpart won't pick it up with their equipment.

I saw an older show about submarines that said they had to use exercise bikes instead of treadmills. Repetitive running was easy to pick up.

This doesn't surprise me.

In general, underwater sound attenuates more quickly as you increase its frequency. Foot-fall thumping has a pretty strong low-frequency component. It's also repetitious, which (I'm guessing but don't know for sure) probably makes it easier for a sonar operator to notice.

Sonar operators are pretty cool. I saw a clip where they identified another ship (or sub) because they heard a valve open or close. It sounded and looked like static to me but they said it was pretty clear to the trained ear.

And then the sonar operator records the sound onto a cassette tape and plays it at 10x speed for the captain to convince them that they really are chasing another submarine.

I love that movie so much...

A low repetition thump is not the same as a low frequency sound.

A thump can be a pulse of high frequency sound.

Right, but IIUC it's the difference between a "transient" [0] and a "tonal" [1], which AFAIK is an important distinction for sonar operators.

[0] https://en.wikipedia.org/wiki/Transient_(acoustics)

This is not true.

Source: I've used a treadmill on a submarine.

The uniform hasn't changed so slippers are there, guys in Northern fleet usually don't have conditions to wear those.

And the US built a global network of microphones to track them called SOSUS.

https://en.wikipedia.org/wiki/SOSUS

The lack of detail is disappointing, but not entirely surprising given the historical context. The SOFAR channel in the ocean transmits low frequency sound waves for thousands of miles. Its existence and applications were kept classified until the 90s.

https://en.wikipedia.org/wiki/SOFAR_channel

There's a great episode from the Cosmos series where Carl Sagan talks about how the range of whale communication was inhibited by the development of steam engine ships: https://youtu.be/UwzukFBWxu4?t=765

100km in some circumstances, and 40km easily? https://www.cgg.com/technicalDocuments/cggv_0000027562.pdf That's a pretty loud "noise" though.

If I were to guess, I think the temperature differential within the water layers make for sound to refract and diffuse quickly and not really travel in a straight line for too long.

Sperm whales click at up to 230 decibels, so yes - the oceans can be quite loud.

Slightly related, but I remember NOAA used to have hydrophones streaming live to the internet and I would listen to them to fall asleep. One day one of the hydrophone lines was cut, and they stopped the stream and never restarted it.