Sonar Pings - can you hear them?

[Neko_Oni]

Okay, I was watching an anime yesterday (Full Metal Panic) and a sub gets pinged by an attack sub. Inside the sub the crew can hear the ping hit. Now this occurs in other shows/movies as well.

My question is, isn't sonar beyond human hearing and if so why would you be able to hear it? Or is this a brain bug of directors?

[Mr Bean]

Active Sonar you can hear, and oh boy will you HEAR it.

Want to know what its like? You can hear it at home kids!

Get a metal garbabe pail. Get a spoon, put the pail over your head, now hit the pail REAL hard with the spoon. Thats what it feels/sounds like.

[Neko_Oni]

So is it more the hull ringing from the ping, as opposed to the ping itself that you hear?

[Adrian Laguna]

On a related note: when I see a submarine or sonar screen on TV it is ussually accompanied by this high-pitched sound that goes: ping... ping... ping... ping... Does it have any bearing on real life?

[TheDarkOne]

So is it more the hull ringing from the ping, as opposed to the ping itself that you hear?

They're basically the same thing...If you hear sound through something, for instance a window or a wall, do you think "oh that's not actually the sound, it's the window ringing from the sound'.

[Admiral Valdemar]

Watch The Hunt For Red October. Near the end, Ramius and Ryan are on separate boats and communicate via sonar pings for yes or no. The strange ominous sound that accompanies each "ping" of the sonar is what you'd hear typically. Since active sonar is rarely used for stealth reasons, you tend to just rely on hydrophones picking up passive sound, though if a torpedo is in the water and goes active with its own sonar, you should pick it up quite readily.

Don't forget, people stopped using frogmen to attack boats openly when they found out a sonar ping could kill any nearby organisms, or at least give them a headache they'll never forget.

[CaptJodan]

On a related note: when I see a submarine or sonar screen on TV it is ussually accompanied by this high-pitched sound that goes: ping... ping... ping... ping... Does it have any bearing on real life?

I think I know what you're refering to. A lot of times, especially in older movies and in most cartoons, the way they denote a submarine is by this consant pinging sound inside the sub even while under way, far away from enemies or other allies. Almost as if the sub itself is sending out active pings to "see" where it's going.

This is completely and totally unrealistic, most especially in combat conditions. You want to avoid making ANY noise, and thus such noises would ONLY be external, and wouldn't necessarily be constant. (For example, WWII destroyers had a cone of sound that they blasted out. Once the destroyer passed overhead of the sub, the pinging stopped because they didn't use active behind them. Generally speaking, you still don't send an active signal down the bearing of your prop wash anyway)

I play too much Silent Hunter III and Dangerous Waters.

[Stark]

Do modern pings sound like just single-note 'pings' or is it a more complex noise?

[Admiral Valdemar]

Why would you need a complicated concerto when a single acoustic return is what you require? It's like beaming out an episode of Who Wants To Be A Millionaire? over your radar dish rather than a simple flash of RF energy. A single note will suffice, not Yankee Doodle Dandy.

[kheegster]

Why would you need a complicated concerto when a single acoustic return is what you require? It's like beaming out an episode of Who Wants To Be A Millionaire? over your radar dish rather than a simple flash of RF energy. A single note will suffice, not Yankee Doodle Dandy.

Wrong...there are wave properties such as interference etc that cannot be exploited with simple monochromatic pulses.

I do not know much about sonars, but as an example I do know of, space-borne radar altimeters usually emit their pulses in varying sequences of differing frequencies in order to maximise measurement precision. Another example that pops to mind is side-ways looking airborne radar (SLAR): they use high frequency 'chips' to create interference patterns in the reflected signal to vastly improve spatial resolution.

[kheegster]

Correction: I just realised that in the case of radar altimeters, there usually isn't any clever pattern of pulses used (although they have to account for transmission through the atmosphere and ionosphere when choosing the frequency), but it is important to use a very short pulse, or else the reflection would be washed out.

My point about SLAR still stands though.

[kheegster]

Eek...just noticed a typo in my first post...it should be high-frequency 'chirps not 'chips'!

[Admiral Valdemar]

Wrong...there are wave properties such as interference etc that cannot be exploited with simple monochromatic pulses.

I do not know much about sonars, but as an example I do know of, space-borne radar altimeters usually emit their pulses in varying sequences of differing frequencies in order to maximise measurement precision. Another example that pops to mind is side-ways looking airborne radar (SLAR): they use high frequency 'chips' to create interference patterns in the reflected signal to vastly improve spatial resolution.

That's equivalent to ironing out the interference in atmospheric distortions picked up by telescopes that use adaptive optics. I was dispelling with the assumption that a melody of sorts would be used rather than a concise and tailored pulse, regardless of harmonics. Typically, sonar is not as complex as that; to correct for any disruption, multiple echoes are done sequentially to filter noise. At least, that is how it tends to go from what I've seen. Radar can receive a lot more bandwidth than it outputs as a signal, therefore, the SNR is effect is not really much of an issue with sonar as it is with radar. The fact that radar operates at a large frequency (the multiple "chirps" you mention) to get a significant return from the target compared to sonar having only a single pulse makes the distinction (millimetric radars of a phased nature can output a lot of juice and, because of the speed of light, average the returns for a clear picture. Sonar and by extension sodar cannot do this).

[Admiral Valdemar]

I should add, the closest you would get to radar with sonic based systems is ultrasonics which work at very short range anyway, but far higher frequencies to give more information over many pulses or "pings" than would be possible with a military hunter-killer sonar suite. Doppler effects would be more useful in ultrasonics naturally than standard sonars.

[Exonerate]

Don't forget, people stopped using frogmen to attack boats openly when they found out a sonar ping could kill any nearby organisms, or at least give them a headache they'll never forget.

Really? How exactly does the sound kill them?

[SCRawl]

Don't forget, people stopped using frogmen to attack boats openly when they found out a sonar ping could kill any nearby organisms, or at least give them a headache they'll never forget.

Really? How exactly does the sound kill them?

Sound pressure levels of over 150dB are lethal to humans. As for the mechanism, I don't know, but active sonar easily exceeds this level.

[Dangermouse]

Don't forget, people stopped using frogmen to attack boats openly when they found out a sonar ping could kill any nearby organisms, or at least give them a headache they'll never forget.

Really? How exactly does the sound kill them?

Sound pressure levels of over 150dB are lethal to humans. As for the mechanism, I don't know, but active sonar easily exceeds this level.

From what I can tell, there are couple of ways.

1) High pressure levels at active sonar frequencues can induce resonance vibrations within the lung or other internal organs such as the liver leading to hemorrhage. Air filled structures have a large impedance mismatch to normal tissue (more or less water) so the lungs are particularly vulnerable.

2) Marine mammals have small microbubbles in their tissues. Some studies speculate that sonar can lead to bubble growth causing a form of "the bends." See here for details .

Acoustic energy from high intensity sources can cause damage rather quickly. Even ultrasound can cause temperature rises of 30 degrees C or more in tissue as well cavitate cells.