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Powerful Sonar Causes Deafness In Dolphins
Hugh Pickens writes "Mass strandings of dolphins and whales could be caused because the animals are rendered temporarily deaf by military sonar, experiments have shown. Tests on a captive dolphin have demonstrated that hearing can be lost for up to 40 minutes on exposure to sonar and may explain several strandings of dolphins and whales in the past decade. Most strandings are still thought to be natural events, but the tests strengthen fears that exercises by naval vessels equipped with sonar are responsible for at least some of them. For example, in the Bahamas in March, 2000, 16 Cuvier's beaked whales and Blainville's beaked whales and a spotted dolphin beached during a US navy exercise in which sonar was used intensively for 16 hours (PDF). 'The big question is what causes them to strand,' says Dr. Aran Mooney, of the University of Hawaii. 'What we are looking at are animals whose primary sense is hearing, like ours is seeing. Their ears are the most sensitive organ they have.' In the experiment, scientists fitted a harmless suction cup to the dolphin's head, with a sensor attached that monitored the animal's brainwaves, and when the pings reached 203 decibels and were repeated, the neurological data showed the mammal had become deaf, for its brain no longer responded to sound. 'We definitely showed that there are physiological and some behavioral effects [from repeated, loud sonar], but to extrapolate that into the wild, we don't really know,' said Mooney."
"The deafness, though, was only temporary and the dolphin was not hurt in the experiment, said Mooney." So the experiment is still cruel but obviously no permanent damage. Deafness aside: Loud noise causes disorientation and nausea in humans, so why not in dolphins. BTW: A "singing" Whale produces a sound pressure level of up to 185 dB under water! (s. http://en.wikipedia.org/wiki/Sound_pressure_level#Examples_of_sound_pressure_and_sound_pressure_levels) So 200 sounds extreme but remember its not air we are talking about, but water. For comparison the hearing threshhold of a diver is 67dB at 1khz. The auditory threshhold through the air at 1khz is 0 dB.
WRT to all of the "203 decibels, OMG!" comments: water decibels aren't the same as SPL decibels.
A decibel is the logarithmic relationship between one quantity and a reference quantity. For sound pressure level, we use the RMS pressure of the sound wave compared to a reference pressure that represents the threshold of human hearing (20 microPa): 20*Log10(P/20e-6)
Other types of decibels use different reference quantities. For example, vibration velocity in the USA uses a reference quantify of 10^-6 in/sec. Sound intensity (sound power through a unit area) uses a reference quantity of 10^-12 W/m2. So comparing sad sound intensity decibels to vibration velocity decibels is meaningless without normalizing the units.
In the case of water decibels, we use pressure as we do for SPL in air, but the reference quantity is different: for water, the reference quantity is typically 1 microPa. Therefore the 203 dB in water is approximately equivalent to about 170 dB SPL in air. Of course you still can't directly compare water dB to SPL because the wavelengths of sound in water are so much longer than wavelengths of sound in air.
In any event, 203 dB in water is very loud (and obviously harmful to aquatic life as demonstrated in the articles), but not necessarily in the same way that 173 dB SPL is loud/harmful to us.
Unfortunately, neither you nor I can assess what "203 decibels" means. That is because that is a meaningless phrase. Here is the information that the AFP left out:
The difference between the reference range measurement and the receiver measurement, assuming spherical spreading (which we're likely to see at a 40m range), is 20 log r, where R is the ratio of the reference range and the receiver range. If the dolphin is 100 m away from a source emitting 203 dB at a 1 yard reference range, it will be hit with acoustic energy at 163 dB (203 - 20 log 100).
By the way, the sound pressure levels you're accustomed to reading about as an land-lubber are probably dB//20 uPa -- i.e., measured in multiples of 20 micropascals. In underwater acoustics we almost always use dB//1 uPa -- i.e., measured in multiples of 1 micropascal. To convert from the in-air numbers to under-water numbers, add 26 dB. A 203 dB sound to an underwater physicist would be a 179 dB to an atmospheric physicist.
Unfortunately I cannot find this article on the Biology Letters web site to check the facts.
Active sonar really doensn't give anything away since once you launch a torpedo, the target, or anyone else in the area, is going to know where the sub is anyway.
What are you basing that assumption on? Modern torpedoes can be programmed to run a lower (i.e: harder to detect) speed until they get close to the target and/or further away from the launch platform. The loudest part of a torpedo launch is the "launch transient", i.e: the sound of the compressed air that pushes it out of the torpedo tube. Some submarines (the Seawolf class) use larger torpedo tubes that allow the torpedo to "swim" out without requiring a blast of compressed air, thus negating most of the noise of a torpedo launch.
Assuming that you are going to detect the launch is a very dangerous assumption in modern naval warfare. Your first indication of incoming "fish" is just as likely to be when they turn on their active seekers at close range and go to full speed. In that scenario you are virtually SOL and don't even have the means to retaliate.
I want peace on earth and goodwill toward man.
We are the United States Government! We don't do that sort of thing.
I'd like someone to explain why active sonar is necessary, being that subs are most effective when their location is not known, and active sonar instantly gives away your location.
Err, active sonar isn't just the domain of submarines. Subs very rarely use it, but sub-hunting aircraft like the SH-60, P-3, Il-18, etc. use combinations of active and passive sonobuoys, as well as dipping sonars (for the helicopters) which have active and passive modes. Surface ships like destroyers will also use active sonar on occasion. Many modern submarines are quiet enough that they can't be heard at all on a passive set, particularly when operating in littoral areas or areas of mixed or disturbed water. If you're the side with the helicopters and destroyers trying to find that submarine, you might have no choice but to blast away on active.
The meek may inherit the earth, but the strong shall take the stars.
The thing of it is, submarines don't use, and don't need a super-powerful active sonar.
This is for surface vessels ("targets" in bubblehead vernacular) searching for subs, not subs hunting each other.
These hyper powerful sonar systems are for surface vessels to locate submarines that may be in the vicinity. When you get into costal areas, the noise of the surf, the temperature gradients (from the shallow bottoms) and the salinity gradients from the fresh water from the rivers, plays havoc with normal sound transmission.
This massive system is used to plow through all that, and still return a signal clear enough to spotlight the sub lurking around the area.
(former US Navy submarine Sonar Tech)
I'm not crazy,I'm actively irresponsible.
Passive sonar, decent stuff at least, is ALWAYS a towed array. Gets the hydrophones away from the ships hull, reducing self noise. That said, I'm not sure exactly which types of vessels carry a towed passive array... destroyers, cruisers, frigates, but i think that's about it. Plus the helo-dropped sonar bouys.
As for as potential enemy capabilities compared to ours, I'm not at liberty to comment one way or the other
I'm not crazy,I'm actively irresponsible.
Wrong. 20dB is 10x the power.
Measuring from 0dB? Are you sure?
From the link a few of us are too lazy to click:
The threshold of hearing is assigned a sound level of 0 decibels (abbreviated 0 dB); this sound corresponds to an intensity of 1*10-12 W/m2. A sound which is 10 times more intense ( 1*10-11 W/m2) is assigned a sound level of 10 dB. A sound which is 10*10 or 100 times more intense ( 1*10-10 W/m2) is assigned a sound level of 20 db. A sound which is 10*10*10 or 1000 times more intense ( 1*10-9 W/m2) is assigned a sound level of 30 db.
Don't tell me to get a life. I'm a gamer; I have LOTS of lives!