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by Amezarak 3928 days ago
I have no idea what sonar frequencies are what, but to expand on your point, sonar is basically the only kind of sensor that works underwater. Radar and sight are basically useless.

Sonar is really all you have to see underwater, and is used heavily for scientific purposes, not only military purposes. Ocean-floor mapping is done with sonar. Active sonar of the kind that hurts whales is not in frequent use by deployed military vessels on military or surveillance missions because, while it gets you a good picture, it also announces "HERE I AM!!!" to the entire world.
1 comments
rustynails 3928 days ago
According to Wikipedia, the issue is with (low frequency, active) LFA sonar.

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

I read somewhere it's about 240db. For reference, a jackhammer at about 1m (3.3ft away) is 130db and is classified as Painful for humans,

http://www.asha.org/public/hearing/Noise/

I am not knowledgeable on acoustics, let alone acoustic dissipation or acoustics in water - but I can see logic behind the argument that LFA sonar causes a problem for whales.

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dantillberg 3927 days ago
I did a little digging, and it seems that it's not really appropriate to compare underwater decibel measurements with decibel measurements in air. For example, [0] discusses whales that generate clicks at 230 dB, and suggests that that is "equivalent to 170 decibels on land."

I'm not sure if it's even possible to get to 240 dB in air... Ah, an article on wikipedia sort of backs me up: [1] says that, at 1 atmosphere of pressure in air, the maximum loudness for undistorted sound is around 194 dB. Anything louder would be a shockwave.

[0]: http://news.nationalgeographic.com/news/2003/11/1103_031103_...

[1]: https://en.wikipedia.org/wiki/Sound_pressure

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nitrogen 3928 days ago
Also keep in mind that decibels are logarithmic, so 240dB is 10^(24-13) times as much sound power as 130.
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jleader 3927 days ago
No, you forgot that the d stands for deci (i.e., 1/10th).

So 240dB is 10^(2.4-1.3) times as much sound power as 130dB.

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vonmoltke 3927 days ago
No, nitrogen's math is correct. The conversion from linear to dB is

y = 10 * log(x)

and the conversion back is

x = 10 ^ (y/10)

Every change of 3dB is a doubling or halving of power. Every change of 10dB is an order-of-magnitude change in power.

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nitrogen 3927 days ago
Right, I did 24-13 instead of 240-130. That's 100 billion times the power.
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jleader 3927 days ago
D'oh! Thanks for catching my error!
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