Sonar use is restricted around whales

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Andrew Crane

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Sonar use is restricted around whales
« on: 24/05/2011 04:30:03 »
Andrew Crane  asked the Naked Scientists:

 I'm Andrew and I am a sailor in the royal australian navy where I use sonar to find submarines. We have restrictions on when we can use sonar around whales.

Now an important point to make is that humans have a frequency range in their ears of 20Hz to 20kHz. Whales however, depending on the species, have a lower frequency range in their "ears".

Now sound being played outside of the water will be mostly be reflected, scattered by the surface and absorbed by the air. There is a small amount that will be refracted into the water. This sound in the water will be attenuated by the water by either spherical absorbsion or cylindrical absorbsion which reduce the power of the sound. If there are speakers under the water this would of course change the equation.
In summary whales will not be deafened because the sound is at too high a frequency and the absobsion (transferring sound energy into heat). I hope this answers the question.

Also sound travels about 1500m/s in sea water (at 20degrees C and 35 parts per thousand salinity)
600m/s in air
5000m/s in metal

What do you think?
« Last Edit: 24/05/2011 04:30:03 by _system »


Offline CliffordK

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Sonar use is restricted around whales
« Reply #1 on: 24/05/2011 08:36:01 »
I lost the question.

I thought part of the problem with active sonar was the the sonar pules were sent out with much higher intensity than the whales normal sounds. 

Perhaps sonar is changing, or that there will eventually be low intensity sonar.