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last message about ocean noisewriting

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1994-03-22 · 7 min read · Edit on Pyrite

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last message about ocean noise

``` Date: 31 Mar 1994 02:27:09 GMT From: Pim van Meurs, root@pvanmeur.extern.ucsd.edu Subject: Re: ocean noise experiment will kill marine life by the thousands In article <2ndcdt$4io@network.ucsd.edu> Pim van Meurs, root@pvanmeur.extern.ucsd.edu writes: > > >Let me again post the deposition made by Dr John Potter during the hearing. I >hope this will clear up some of the persistant misunderstandings and >misrepresentations of the ATOC experiment. > >Pim van Meurs >======================================================= > >The ATOC office can be called on (619) 534 2368 and they will provide much >more info. re the marine mammal observation plan (a $3 million effort) and >other relevant info. > >Dr. John R. Potter, Scripps Inst. Oceano. (619) 534 8151 > - 1 - Deposition to the ATOC permit hearing, March 22 1994 > > >Deposition made by Dr. J.R. Potter to the Public Hearing on permit >applications submitted for ATOC, 22 March 1994, Washington D.C. >Tel: (619) 534 8151. Fax: (619) 534 7641. Email johnp@mpl.ucsd.edu > >I am a physical oceanographer and marine acoustician by training, with 15 >year's research experience in these areas. I am a member of the Acoustical >Society of America's committee on the effects of noise on marine mammals >and co-organiser of two conferences, one on ocean variability and acoustic >propagation, the other being the third international conference on Sea >Surface Sound. My current work is on passive acoustic imaging in the ocean >and on marine mammal vocalizations. I am not involved with the ATOC >project and do not derive income or grant support from the ATOC program. I >am motivated to contribute to this public hearing by my personal sense of >commitment to protecting the earth's ecosystem and improving mankind's >attitude towards the environment. I have followed the criticism of the >ATOC experimental program with considerable interest, and it seems to me >that the discussion has been clouded by an insufficient understanding of >the physics of sound propagation in the ocean. I wish to present some >material that I hope will clarify the issue and remove some of the >impediments to an accord between the proponents of the ATOC program and >those concerned individuals who are justifiably calling for an account of >the expected impact on marine mammals. > >There are a number of physics-based issues that I would like to stress with >regard to useful units and measures with which to gauge the potential >acoustic impact of the ATOC program. > >1) The term "dB" is not a unit, but a ratio of values. The values often >chosen for comparison are those of pressure. This is unfortunate, because >pressure alone gives a poor understanding of the effects of a linearly >propagating sound wave. All physiological hearing requires sound energy to >be coupled into body tissues by inducing motion which stimulates auditory >nerves, providing the sense of hearing. The energy available for the >senses is not simply related to pressure. In a given fluid, pressure and >energy are directly related, but when different media are compared (such as >air and water) energy must be used as the comparative unit to remain >meaningful. dB values of pressure in air (referenced to 20 microPascals) >must be increased by some 61.5 dB if they are to be compared to dB pressure >levels in sea water (referenced to 1 microPascal). > >2) Unlike sound in air, which radiates almost as a spherical wave and >suffers high attenuation with range, sound can be arranged to propagate in >water with very little attenuation and in a 'ducted' channel, i.e., in a >confined conduit much like light pulses in an optical fiber. Just as we >are able to use optical fibers to communicate over great distances without >the use of powerful light sources, so we can use sound in the ocean to >communicate over ocean basin scales without the source being extremely >loud. Nevertheless, the ATOC source level is comparable to other separate >contributors in the oceans over the 10-100 Hz frequency band such as >individual ships, volcanoes, storms, polar ice fields, earthquakes, etc. > >3) The ATOC signal processing uses a proven and powerful technique known as >pulse-compression that effectively improves the detectability of the >received signal by a factor of 20-100 times, depending on the coherence of >the transmission. The technique requires exact knowledge of the >transmitted pulse sequence, which must be as long as possible consistent >with coherence scales of the transmission path. This technique enables the >receivers to reliably detect the signal even when it would be completely >masked by other noise sources to a 'casual observer'. It is thus possible >to receive a useful signal which marine mammals would find impossible to >detect. > > >To provide a better appreciation of the sound levels involved, Table I >presents an approximate comparison of some characteristic sound field >pressure and energy levels integrated over 60-90 Hz bandwidth. Some of the >data were provided by Dr. Anne Bowles, the remainder being culled from >publications in the open literature. The table should not be taken to >suggest that hearing sensations can be directly translated from one species >to another. Approximate ATOC integrated pressure levels have been >calculated allowing for initial spherical, then cylindrical spreading with >volume attenuation. > >______________________________________________________________________ >IN AIR Energy > IN SEA WATER >______________________________________________________________________ >Observations SPL in dB Energy flux SPL in dB > Observations > //[20 microPa] [watts/m2] //[1 microPa] >______________________________________________________________________ >Inaudible to humans 0.0 9.5 E-13 61.5 >Absolute minimum ocean >noise in absence of shipping >& less than 7 kts wind >Quiet desert, >human threshold 20.0 9.5 E-11 81.5 >Very quiet ocean ambient > 34.0 2.4 E-9 95.5 >Typical deep ocean noise >ATOC source @ 3500 km >Nighttime quiet in home 40.0 9.5 E-9 101.5 >Near-shore ocean noise level >ATOC source @ 1500 km >Normal received >human speech 58.5 6.7 E-7 120.0 >Approx. 50% mysticetes react. >ATOC source @ 30 km >Safe limit for intermit- >tent human exposure 90.0 9.5 E-4 151.5 >Suggested safe limit for fish >possible temporary hearing >threshold shift in whales. >ATOC source @ 150 m range >Loud music 110.0 9.5 E-2 171.5 >USN continuous safe limit for >humans. >ATOC source @ 15 m range >Military jet flying >at 100 m range 120.0 9.5 E-1 181.5 >USN impulse safe limit for >humans. >ATOC source @ 4.7 m range >Impulse damage >threshold for humans 148.0 6.0 E+2 209.5 Seismic >airgun noise @ 4 m >Rocket noise at 500m 160.0 9.5 E+3 221.5 Seismic >airgun noise @ 1m > >Table I > >Since the ATOC sources will be deployed at some 900 m depth, and source >levels will be ramped up over a period of 5 minutes, Table I indicates no >significant risk of physiological impact on marine mammals, providing that >they make use of the opportunity to swim away in the unlikely event that a >deep-diving mammal should find itself within 150 m or so of a source at >initiation of a transmission. > >Before coming to any conclusions, I would like to reiterate that these >calculated levels and comparisons are approximate and may be in error by >3-6 dB. Certainly my crude calculations of ATOC source strengths will be >inferior to the extensive propagation modelling performed by the ATOC >group, although I am not aware of any substantial discrepancies between >their calculations and my own. > > >It is important to recognise that the ATOC sources will illuminate the deep >ocean sound channel, not the near-surface. The ducted propagation and mode >cut-off will prevent significant sound levels from reaching deep onto the >continental shelf. Only deep-diving marine mammals offshore will be >influenced. In addition, from Table I I have drawn the following >conclusions: > >1) The ATOC experiment is very unlikely to inflict physiological damage on >marine mammals. >2) Given the (very limited) information available on marine mammal >responses to noise, ATOC sources are likely to produce a significant >reaction in marine mammal behaviour at ranges of up to some 30 km. This >affects an area of some 0.002% of the Pacific Ocean, for up to 8% of the >time (the ATOC maximum duty cycle). >3) In order for marine mammals to be able to detect that the (intermittent) >ATOC sources are on, the source level will have to exceed the natural >variability due to periodic volcanic action, storm systems, shipping >variability, etc. This background variability has been estimated to be >typically 6 dB. It is therefore unlikely that any marine mammals will be >able to detect the ATOC sources outside a range of 1500 km, or about 5% of >the Pacific Ocean. >4) The ATOC sources will be undetectable (without prior knowledge of the >exact transmitted wave form) beyond a range of approximately 3500 km, >affecting some 25% of the Pacific Ocean. >5) The ATOC sources are insignificant compared to many other known >anthropogenic noise pollutants in the ocean. The sources are certainly not >the loudest single contributors to anthropogenic noise pollution. A single >large tanker radiates much more power over a wider frequency range, 24 >hours a day when at sea, for some 80% of its lifetime (assuming it spends >20% of its time in port or dry dock), and generally lasts over 10 years. > >It appears that the ATOC sources will not 'flood' the ocean with sound, but >I believe that it is possible that deep-diving marine mammals with good >hearing sensitivity in the 60-90 Hz bandwidth will, in principle, be able >to detect a change in the statistical nature of the ambient noise in >approximately 5% of the Pacific Ocean when the sources are transmitting. > > > > > >------------------------------------------- >Pim van Meurs >pim@nepac.ucsd.edu ```

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