Ocean acoustic tomography

Last updated
The western North Atlantic showing the locations of two experiments that employed ocean acoustic tomography. AMODE, the "Acoustic Mid-Ocean Dynamics Experiment" (1990-1), was designed to study ocean dynamics in an area away from the Gulf Stream, and SYNOP (1988-9) was designed to synoptically measure aspects of the Gulf Stream. The colors show a snapshot of sound speed at 300 metres (980 ft) depth derived from a high-resolution numerical ocean model. One of the key motivations for employing tomography is that the measurements give averages over the turbulent ocean. Tomography atlantic.png
The western North Atlantic showing the locations of two experiments that employed ocean acoustic tomography. AMODE, the "Acoustic Mid-Ocean Dynamics Experiment" (1990-1), was designed to study ocean dynamics in an area away from the Gulf Stream, and SYNOP (1988-9) was designed to synoptically measure aspects of the Gulf Stream. The colors show a snapshot of sound speed at 300 metres (980 ft) depth derived from a high-resolution numerical ocean model. One of the key motivations for employing tomography is that the measurements give averages over the turbulent ocean.

Ocean acoustic tomography is a technique used to measure temperatures and currents over large regions of the ocean. [1] [2] On ocean basin scales, this technique is also known as acoustic thermometry. The technique relies on precisely measuring the time it takes sound signals to travel between two instruments, one an acoustic source and one a receiver, separated by ranges of 100–5,000 kilometres (54–2,700 nmi). If the locations of the instruments are known precisely, the measurement of time-of-flight can be used to infer the speed of sound, averaged over the acoustic path. Changes in the speed of sound are primarily caused by changes in the temperature of the ocean, hence the measurement of the travel times is equivalent to a measurement of temperature. A 1 °C (1.8 °F) change in temperature corresponds to about 4 metres per second (13 ft/s) change in sound speed. An oceanographic experiment employing tomography typically uses several source-receiver pairs in a moored array that measures an area of ocean.

Contents

Motivation

Seawater is an electrical conductor, so the oceans are opaque to electromagnetic energy (e.g., light or radar). The oceans are fairly transparent to low-frequency acoustics, however. The oceans conduct sound very efficiently, particularly sound at low frequencies, i.e., less than a few hundred hertz. [3] These properties motivated Walter Munk and Carl Wunsch [4] [5] to suggest "acoustic tomography" for ocean measurement in the late 1970s. The advantages of the acoustical approach to measuring temperature are twofold. First, large areas of the ocean's interior can be measured by remote sensing. Second, the technique naturally averages over the small scale fluctuations of temperature (i.e., noise) that dominate ocean variability.

From its beginning, the idea of observations of the ocean by acoustics was married to estimation of the ocean's state using modern numerical ocean models and the techniques assimilating data into numerical models. As the observational technique has matured, so too have the methods of data assimilation and the computing power required to perform those calculations.

Multipath arrivals and tomography

Propagation of acoustic ray paths through the ocean. From the acoustic source at left, the paths are refracted by faster sound speed above and below the SOFAR channel, hence they oscillate about the channel axis. Tomography exploits these "multipaths" to infer information about temperature variations as a function of depth. Note that the aspect ratio of the figure has been greatly skewed to better illustrate the rays; the maximum depth of the figure is only 4.5 km, while the maximum range is 500 km. Rays test.gif
Propagation of acoustic ray paths through the ocean. From the acoustic source at left, the paths are refracted by faster sound speed above and below the SOFAR channel, hence they oscillate about the channel axis. Tomography exploits these "multipaths" to infer information about temperature variations as a function of depth. Note that the aspect ratio of the figure has been greatly skewed to better illustrate the rays; the maximum depth of the figure is only 4.5 km, while the maximum range is 500 km.

One of the intriguing aspects of tomography is that it exploits the fact that acoustic signals travel along a set of generally stable ray paths. From a single transmitted acoustic signal, this set of rays gives rise to multiple arrivals at the receiver, the travel time of each arrival corresponding to a particular ray path. The earliest arrivals correspond to the deeper-traveling rays, since these rays travel where sound speed is greatest. The ray paths are easily calculated using computers ("ray tracing"), and each ray path can generally be identified with a particular travel time. The multiple travel times measure the sound speed averaged over each of the multiple acoustic paths. These measurements make it possible to infer aspects of the structure of temperature or current variations as a function of depth. The solution for sound speed, hence temperature, from the acoustic travel times is an inverse problem.

The integrating property of long-range acoustic measurements

Ocean acoustic tomography integrates temperature variations over large distances, that is, the measured travel times result from the accumulated effects of all the temperature variations along the acoustic path, hence measurements by the technique are inherently averaging. This is an important, unique property, since the ubiquitous small-scale turbulent and internal-wave features of the ocean usually dominate the signals in measurements at single points. For example, measurements by thermometers (i.e., moored thermistors or Argo drifting floats) have to contend with this 1-2 °C noise, so that large numbers of instruments are required to obtain an accurate measure of average temperature. For measuring the average temperature of ocean basins, therefore, the acoustic measurement is quite cost effective. Tomographic measurements also average variability over depth as well, since the ray paths cycle throughout the water column.

Reciprocal tomography

"Reciprocal tomography" employs the simultaneous transmissions between two acoustic transceivers. A "transceiver" is an instrument incorporating both an acoustic source and a receiver. The slight differences in travel time between the reciprocally-traveling signals are used to measure ocean currents, since the reciprocal signals travel with and against the current. The average of these reciprocal travel times is the measure of temperature, with the small effects from ocean currents entirely removed. Ocean temperatures are inferred from the sum of reciprocal travel times, while the currents are inferred from the difference of reciprocal travel times. Generally, ocean currents (typically 10 cm/s (3.9 in/s)) have a much smaller effect on travel times than sound speed variations (typically 5 m/s (16 ft/s)), so "one-way" tomography measures temperature to good approximation.

Applications

In the ocean, large-scale temperature changes can occur over time intervals from minutes (internal waves) to decades (oceanic climate change). Tomography has been employed to measure variability over this wide range of temporal scales and over a wide range of spatial scales. Indeed, tomography has been contemplated as a measurement of ocean climate using transmissions over antipodal distances. [3]

Tomography has come to be a valuable method of ocean observation, [6] exploiting the characteristics of long-range acoustic propagation to obtain synoptic measurements of average ocean temperature or current. One of the earliest applications of tomography in ocean observation occurred in 1988-9. A collaboration between groups at the Scripps Institution of Oceanography and the Woods Hole Oceanographic Institution deployed a six-element tomographic array in the abyssal plain of the Greenland Sea gyre to study deep water formation and the gyre circulation. [7] [8] Other applications include the measurement of ocean tides, [9] [10] and the estimation of ocean mesoscale dynamics by combining tomography, satellite altimetry, and in situ data with ocean dynamical models. [11] In addition to the decade-long measurements obtained in the North Pacific, acoustic thermometry has been employed to measure temperature changes of the upper layers of the Arctic Ocean basins, [12] which continues to be an area of active interest. [13] Acoustic thermometry was also recently been used to determine changes to global-scale ocean temperatures using data from acoustic pulses sent from one end of the Earth to the other. [14] [15]

Acoustic thermometry

Acoustic thermometry is an idea to observe the world's ocean basins, and the ocean climate in particular, using trans-basin acoustic transmissions. "Thermometry", rather than "tomography", has been used to indicate basin-scale or global scale measurements. Prototype measurements of temperature have been made in the North Pacific Basin and across the Arctic Basin. [1]

Starting in 1983, John Spiesberger of the Woods Hole Oceanographic Institution, and Ted Birdsall and Kurt Metzger of the University of Michigan developed the use of sound to infer information about the ocean's large-scale temperatures, and in particular to attempt the detection of global warming in the ocean. This group transmitted sounds from Oahu that were recorded at about ten receivers stationed around the rim of the Pacific Ocean over distances of 4,000 km (2,500 mi). [16] [17] These experiments demonstrated that changes in temperature could be measured with an accuracy of about 20 millidegrees. Spiesberger et al. did not detect global warming. Instead they discovered that other natural climatic fluctuations, such as El Nino, were responsible in part for substantial fluctuations in temperature that may have masked any slower and smaller trends that may have occurred from global warming. [18]

The Acoustic Thermometry of Ocean Climate (ATOC) program was implemented in the North Pacific Ocean, with acoustic transmissions from 1996 through fall 2006. The measurements terminated when agreed-upon environmental protocols ended. The decade-long deployment of the acoustic source showed that the observations are sustainable on even a modest budget. The transmissions have been verified to provide an accurate measurement of ocean temperature on the acoustic paths, with uncertainties that are far smaller than any other approach to ocean temperature measurement. [19] [20]

Repeating earthquakes acting as naturally-occurring acoustic sources have also been used in acoustic thermometry, which may be particularly useful for inferring temperature variability in the deep ocean which is presently poorly sampled by in-situ instruments. [21]

The ATOC prototype array was an acoustic source located just north of Kauai, Hawaii, and transmissions were made to receivers of opportunity in the North Pacific Basin. The source signals were broadband with frequencies centered on 75 Hz and a source level of 195 dB re 1 micropascal at 1 m, or about 250 watts. Six transmissions of 20-minute duration were made on every fourth day. KauaiArray2.GIF
The ATOC prototype array was an acoustic source located just north of Kauai, Hawaii, and transmissions were made to receivers of opportunity in the North Pacific Basin. The source signals were broadband with frequencies centered on 75 Hz and a source level of 195 dB re 1 micropascal at 1 m, or about 250 watts. Six transmissions of 20-minute duration were made on every fourth day.

Acoustic transmissions and marine mammals

The ATOC project was embroiled in issues concerning the effects of acoustics on marine mammals (e.g. whales, porpoises, sea lions, etc.). [22] [23] [24] Public discussion was complicated by technical issues from a variety of disciplines (physical oceanography, acoustics, marine mammal biology, etc.) that makes understanding the effects of acoustics on marine mammals difficult for the experts, let alone the general public. Many of the issues concerning acoustics in the ocean and their effects on marine mammals were unknown. Finally, there were a variety of public misconceptions initially, such as a confusion of the definition of sound levels in air vs. sound levels in water. If a given number of decibels in water are interpreted as decibels in air, the sound level will seem to be orders of magnitude larger than it really is - at one point the ATOC sound levels were erroneously interpreted as so loud the signals would kill 500,000 animals. [25] [5] The sound power employed, 250 W, was comparable those made by blue or fin whales, [24] although those whales vocalize at much lower frequencies. The ocean carries sound so efficiently that sounds do not have to be that loud to cross ocean basins. Other factors in the controversy were the extensive history of activism where marine mammals are concerned, stemming from the ongoing whaling conflict, and the sympathy that much of the public feels toward marine mammals. [25]

As a result of this controversy, the ATOC program conducted a $6 million study of the effects of the acoustic transmissions on a variety of marine mammals. The acoustic source was mounted on the bottom about a half mile deep, hence marine mammals, which are bound to the surface, were generally further than a half mile from the source. The source level was modest, less than the sound level of large whales, and the duty cycle was 2% (i.e., the sound is on only 2% of the day). [26] After six years of study the official, formal conclusion from this study was that the ATOC transmissions have "no biologically significant effects". [24] [27] [28]

Other acoustics activities in the ocean may not be so benign insofar as marine mammals are concerned. Various types of man-made sounds have been studied as potential threats to marine mammals, such as airgun shots for geophysical surveys, [29] or transmissions by the U.S. Navy for various purposes. [30] The actual threat depends on a variety of factors beyond noise levels: sound frequency, frequency and duration of transmissions, the nature of the acoustic signal (e.g., a sudden pulse, or coded sequence), depth of the sound source, directionality of the sound source, water depth and local topography, reverberation, etc.

Types of transmitted acoustic signals

Tomographic transmissions consist of long coded signals (e.g., "m-sequences") lasting 30 seconds or more. The frequencies employed range from 50 to 1000 Hz and source powers range from 100 to 250 W, depending on the particular goals of the measurements. With precise timing such as from GPS, travel times can be measured to a nominal accuracy of 1 millisecond. While these transmissions are audible near the source, beyond a range of several kilometers the signals are usually below ambient noise levels, requiring sophisticated spread-spectrum signal processing techniques to recover them.

See also

Related Research Articles

<span class="mw-page-title-main">Acoustics</span> Branch of physics involving mechanical waves

Acoustics is a branch of physics that deals with the study of mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical engineer. The application of acoustics is present in almost all aspects of modern society with the most obvious being the audio and noise control industries.

<span class="mw-page-title-main">Sonar</span> Acoustic sensing method

Sonar is a technique that uses sound propagation to navigate, measure distances (ranging), communicate with or detect objects on or under the surface of the water, such as other vessels.

In physics, attenuation is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable attenuation rates.

<span class="mw-page-title-main">Echo sounding</span> Measuring the depth of water by transmitting sound waves into water and timing the return

Echo sounding or depth sounding is the use of sonar for ranging, normally to determine the depth of water (bathymetry). It involves transmitting acoustic waves into water and recording the time interval between emission and return of a pulse; the resulting time of flight, along with knowledge of the speed of sound in water, allows determining the distance between sonar and target. This information is then typically used for navigation purposes or in order to obtain depths for charting purposes.

<span class="mw-page-title-main">Bioacoustics</span> Study of sound relating to biology

Bioacoustics is a cross-disciplinary science that combines biology and acoustics. Usually it refers to the investigation of sound production, dispersion and reception in animals. This involves neurophysiological and anatomical basis of sound production and detection, and relation of acoustic signals to the medium they disperse through. The findings provide clues about the evolution of acoustic mechanisms, and from that, the evolution of animals that employ them.

<span class="mw-page-title-main">Whale vocalization</span> Sounds produced by whales

Whales use a variety of sounds for communication and sensation. The mechanisms used to produce sound vary from one family of cetaceans to another. Marine mammals, including whales, dolphins, and porpoises, are much more dependent on sound than land mammals due to the limited effectiveness of other senses in water. Sight is less effective for marine mammals because of the way particulates in the ocean scatter light. Smell is also limited, as molecules diffuse more slowly in water than in air, which makes smelling less effective. However, the speed of sound is roughly four times greater in water than in the atmosphere at sea level. As sea mammals are so dependent on hearing to communicate and feed, environmentalists and cetologists are concerned that they are being harmed by the increased ambient noise in the world's oceans caused by ships, sonar and marine seismic surveys.

<span class="mw-page-title-main">SOFAR channel</span> Horizontal layer of water in the ocean at which depth the speed of sound is at its minimum

The SOFAR channel, or deep sound channel (DSC), is a horizontal layer of water in the ocean at which depth the speed of sound is at its minimum. The SOFAR channel acts as a waveguide for sound, and low frequency sound waves within the channel may travel thousands of miles before dissipating. An example was reception of coded signals generated by the Navy chartered ocean surveillance vessel Cory Chouest off Heard Island, located in the southern Indian Ocean, by hydrophones in portions of all five major ocean basins and as distant as the North Atlantic and North Pacific.

An acoustic doppler current profiler (ADCP) is a hydroacoustic current meter similar to a sonar, used to measure water current velocities over a depth range using the Doppler effect of sound waves scattered back from particles within the water column. The term ADCP is a generic term for all acoustic current profilers, although the abbreviation originates from an instrument series introduced by RD Instruments in the 1980s. The working frequencies range of ADCPs range from 38 kHz to several megahertz.

<span class="mw-page-title-main">Walter Munk</span> American oceanographer (1917–2019)

Walter Heinrich Munk was an American physical oceanographer. He was one of the first scientists to bring statistical methods to the analysis of oceanographic data. Munk worked on a wide range of topics, including surface waves, geophysical implications of variations in the Earth's rotation, tides, internal waves, deep-ocean drilling into the sea floor, acoustical measurements of ocean properties, sea level rise, and climate change. His work won awards including the National Medal of Science, the Kyoto Prize, and induction to the French Legion of Honour.

Gary Edward John Bold was a New Zealand physicist, as of 2009 an Honorary Associate Professor in physics at the University of Auckland. After gaining a PhD in 1961, Bold became a lecturer who taught across all courses in the physics department at the University. His research areas included underwater acoustics and application of physics theory to understanding human consciousness. He was highly regarded as a teacher and won the Prime Minister's Supreme Award at the 2004 Tertiary Teaching Excellence Awards. Bold had an interest in amateur radio and as an active member of the New Zealand Association of Radio Transmitters (NZART), won a prize for the quality of his columns in the organisation's newsletters.

<span class="mw-page-title-main">Underwater acoustics</span> Study of the propagation of sound in water

Underwater acoustics is the study of the propagation of sound in water and the interaction of the mechanical waves that constitute sound with the water, its contents and its boundaries. The water may be in the ocean, a lake, a river or a tank. Typical frequencies associated with underwater acoustics are between 10 Hz and 1 MHz. The propagation of sound in the ocean at frequencies lower than 10 Hz is usually not possible without penetrating deep into the seabed, whereas frequencies above 1 MHz are rarely used because they are absorbed very quickly.

The ASA Silver Medal is an award presented by the Acoustical Society of America to individuals, without age limitation, for contributions to the advancement of science, engineering, or human welfare through the application of acoustic principles or through research accomplishments in acoustics. The medal is awarded in a number of categories depending on the technical committee responsible for making the nomination.

<span class="mw-page-title-main">Sound</span> Vibration that travels via pressure waves in matter

In physics, sound is a vibration that propagates as an acoustic wave through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the reception of such waves and their perception by the brain. Only acoustic waves that have frequencies lying between about 20 Hz and 20 kHz, the audio frequency range, elicit an auditory percept in humans. In air at atmospheric pressure, these represent sound waves with wavelengths of 17 meters (56 ft) to 1.7 centimeters (0.67 in). Sound waves above 20 kHz are known as ultrasound and are not audible to humans. Sound waves below 20 Hz are known as infrasound. Different animal species have varying hearing ranges.

The POLYGON experiment was a pioneer experiment in oceanography conducted in the middle of the Atlantic Ocean during the 1970s. The experiment, led by Leonid Brekhovskikh, was the first to establish the existence of so-called mesoscale eddies, eddies at the 100 km (60 mi) and 100-day scale, which triggered the "mesoscale revolution". The existence of mesoscale eddies was predicted by Henry Stommel in the 1960s, but there was no way to observe them with traditional sampling methods.

<span class="mw-page-title-main">JASCO Applied Sciences</span>

JASCO Applied Sciences provides scientific consulting services and equipment related to underwater acoustics. JASCO operates from 7 international locations and provides services to the oil and gas, marine construction, energy, renewable energy, fisheries, maritime transport and defence sectors. The head office is located in Halifax, NS Canada. JASCO employs acousticians, bioacousticians, physicists, marine mammal scientists, engineers, technologists, and project managers.

<span class="mw-page-title-main">Kelly Benoit-Bird</span> Marine scientist

Kelly Benoit-Bird is a marine scientist and senior scientist at the Monterey Bay Aquarium Research Institute. Benoit-Bird uses acoustics to study marine organisms and was named a MacArthur Fellow in 2010.

Stanley Martin Flatté was a particle physicist and expert on wave propagation in atmospheric optics, ocean acoustics, and seismology.

<span class="mw-page-title-main">Christine Erbe</span> German-Australian physicist

Christine Erbe is a German-Australian physicist specializing in underwater acoustics. She is a professor in the School of Earth and Planetary Sciences and director of the Centre for Marine Science and Technology (CMST)—both at Curtin University in Perth, Western Australia. Erbe is known for her research on acoustic masking in marine mammals, investigating how man-made underwater noise interferes with animal acoustic communication.

<span class="mw-page-title-main">Seismic oceanography</span>

Seismic oceanography is a form of acoustic oceanography, in which sound waves are used to study the physical properties and dynamics of the ocean. It provides images of changes in the temperature and salinity of seawater. Unlike most oceanographic acoustic imaging methods, which use sound waves with frequencies greater than 10,000 Hz, seismic oceanography uses sound waves with frequencies lower than 500 Hz. Use of low-frequency sound means that seismic oceanography is unique in its ability to provide highly detailed images of oceanographic structure that span horizontal distances of hundreds of kilometres and which extend from the sea surface to the seabed. Since its inception in 2003, seismic oceanography has been used to image a wide variety of oceanographic phenomena, including fronts, eddies, thermohaline staircases, turbid layers and cold methane seeps. In addition to providing spectacular images, seismic oceanographic data have given quantitative insight into processes such as movement of internal waves and turbulent mixing of seawater.

<span class="mw-page-title-main">MERMAID</span>

MERMAID is a marine scientific instrument platform, short for Mobile Earthquake Recorder for Marine Areas by Independent Divers.

References

  1. 1 2 Munk, Walter; Peter Worcester; Carl Wunsch (1995). Ocean Acoustic Tomography. Cambridge: Cambridge University Press. ISBN   978-0-521-47095-7.
  2. ↑ Walter Sullivan (1987-07-28). "Vast Effort Aims to Reveal Oceans' Hidden Patterns". New York Times. Retrieved 2007-11-05.
  3. 1 2 "The Heard Island Feasibility Test". Acoustical Society of America. 1994.
  4. ↑ Munk, Walter; Carl Wunsch (1982). "Observing the ocean in the 1990s". Phil. Trans. R. Soc. Lond. A. 307 (1499): 439–464. Bibcode:1982RSPTA.307..439M. doi:10.1098/rsta.1982.0120. S2CID   122989068.
  5. 1 2 Munk, Walter (2006). "Ocean Acoustic Tomography; from a stormy start to an uncertain future". In Jochum, Markus; Murtugudde, Raghu (eds.). Physical Oceanography: Developments Since 1950. New York: Springer. pp. 119–136. ISBN   9780387331522.
  6. ↑ Fischer, A.S.; Hall, J.; Harrison, D.E.; Stammer, D.; Benveniste, J. (2010). "Conference Summary-Ocean Information for Society: Sustaining the Benefits, Realizing the Potential". In Hall, J.; Harrison, D.E.; Stammer, D. (eds.). Proceedings of OceanObs'09: Sustained Ocean Observations and Information for Society (Vol. 1). ESA Publication WPP-306.
  7. ↑ Pawlowicz, R.; et al. (1995-03-15). "Thermal evolution of the Greenland Sea gyre in 1988-1989". Vol. 100. Journal of Geophysical Research. pp. 4727–2750.
  8. ↑ Morawitz, W. M. L.; et al. (1996). "Three-dimensional observations of a deep convective chimney in the Greenland Sea during winter 1988/1989". Vol. 26. Journal of Physical Oceanography. pp. 2316–2343.
  9. ↑ Stammer, D.; et al. (2014). "Accuracy assessment of global barotropic ocean tide models". Reviews of Geophysics. 52 (3): 243–282. Bibcode:2014RvGeo..52..243S. doi:10.1002/2014RG000450. hdl: 2027.42/109077 . S2CID   18056807.
  10. ↑ Dushaw, B.D.; Worcester, P.F.; Dzieciuch, M.A. (2011). "On the predictability of mode-1 internal tides". Deep-Sea Research Part I. 58 (6): 677–698. Bibcode:2011DSRI...58..677D. doi:10.1016/j.dsr.2011.04.002.
  11. ↑ Lebedev, K.V.; Yaremchuck, M.; Mitsudera, H.; Nakano, I.; Yuan, G. (2003). "Monitoring the Kuroshio Extension through dynamically constrained synthesis of the acoustic tomography, satellite altimeter and in situ data". Journal of Physical Oceanography. 59 (6): 751–763. doi:10.1023/b:joce.0000009568.06949.c5. S2CID   73574827.
  12. ↑ Mikhalevsky, P. N.; Gavrilov, A.N. (2001). "Acoustic thermometry in the Arctic Ocean". Polar Research. 20 (2): 185–192. Bibcode:2001PolRe..20..185M. doi: 10.3402/POLAR.V20I2.6516 . S2CID   218986875.
  13. ↑ Mikhalevsky, P. N.; Sagan, H.; et al. (2001). "Multipurpose acoustic networks in the integrated Arctic Ocean observing system". Arctic. 28, Suppl. 1 (5): 17 pp. doi:10.14430/arctic4449. hdl: 20.500.11937/9445 . Archived from the original on September 10, 2015. Retrieved April 24, 2015.
  14. ↑ Munk, W.H.; O'Reilly, W.C.; Reid, J.L. (1988). "Australia-Bermuda Sound Transmission Experiment (1960) Revisited". Journal of Physical Oceanography. 18 (12): 1876–1998. Bibcode:1988JPO....18.1876M. doi: 10.1175/1520-0485(1988)018<1876:ABSTER>2.0.CO;2 .
  15. ↑ Dushaw, B.D.; Menemenlis, D. (2014). "Antipodal acoustic thermometry: 1960, 2004". Deep-Sea Research Part I. 86: 1–20. Bibcode:2014DSRI...86....1D. doi: 10.1016/j.dsr.2013.12.008 .
  16. ↑ Spiesberger, john; Kurt Metzter (1992). "Basin scale ocean monitoring with acoustic thermometers". Oceanography. 5 (2): 92–98. doi: 10.5670/oceanog.1992.15 .
  17. ↑ Spiesberger, J.L.; K. Metzger (1991). "Basin-scale tomography: A new tool for studying weather and climate". J. Geophys. Res. 96 (C3): 4869–4889. Bibcode:1991JGR....96.4869S. doi:10.1029/90JC02538.
  18. ↑ Spiesberger, John; Harley Hurlburt; Mark Johnson; Mark Keller; Steven Meyers; and J.J. O'Brien (1998). "Acoustic thermometry data compared with two ocean models: The importance of Rossby waves and ENSO in modifying the ocean interior". Dynamics of Atmospheres and Oceans. 26 (4): 209–240. Bibcode:1998DyAtO..26..209S. doi:10.1016/s0377-0265(97)00044-4.
  19. ↑ The ATOC Consortium (1998-08-28). "Ocean Climate Change: Comparison of Acoustic Tomography, Satellite Altimetry, and Modeling". Science Magazine. pp. 1327–1332. Retrieved 2007-05-28.
  20. ↑ Dushaw, Brian; et al. (2009-07-19). "A decade of acoustic thermometry in the North Pacific Ocean". Journal of Geophysical Research. Vol. 114, C07021. J. Geophys. Res. Bibcode:2009JGRC..114.7021D. doi:10.1029/2008JC005124.
  21. ↑ Wu, Wenbo; Zhan, Zhongwen; Peng, Shirui; Ni, Sidao; Callies, Jörn (2020-09-18). "Seismic ocean thermometry". Science. 369 (6510): 1510–1515. Bibcode:2020Sci...369.1510W. doi:10.1126/science.abb9519. ISSN   0036-8075. PMID   32943525. S2CID   219887722.
  22. ↑ Stephanie Siegel (June 30, 1999). "Low-frequency sonar raises whale advocates' hackles". CNN. Retrieved 2007-10-23.
  23. ↑ Malcolm W. Browne (June 30, 1999). "Global Thermometer Imperiled by Dispute". NY Times. Retrieved 2007-10-23.
  24. 1 2 3 Kenneth Chang (June 24, 1999). "An Ear to Ocean Temperature". ABC News. Archived from the original on 2003-10-06. Retrieved 2007-10-23.
  25. 1 2 Potter, J. R. (1994). "ATOC: Sound Policy or Enviro-Vandalism? Aspects of a Modern Media-Fueled Policy Issue". The Journal of Environment & Development. 3 (2): 47–62. doi:10.1177/107049659400300205. S2CID   154909187 . Retrieved 2009-11-20.
  26. ↑ Curtis, K. R.; B. M. Howe; J. A. Mercer (1999). "Low-frequency ambient sound in the North Pacific: Long timeseries observations" (PDF). Journal of the Acoustical Society of America. 106 (6): 3189–3200. Bibcode:1999ASAJ..106.3189C. doi:10.1121/1.428173 . Retrieved 2020-06-30.
  27. ↑ Clark, C. W.; D. E. Crocker; J. Gedamke; P. M. Webb (2003). "The effect of a low-frequency sound source (acoustic thermometry of the ocean climate) on the diving behavior of juvenile northern elephant seals, Mirounga angustirostris". Journal of the Acoustical Society of America. 113 (2): 1155–1165. Bibcode:2003ASAJ..113.1155C. doi:10.1121/1.1538248. hdl: 10211.3/124720 . PMID   12597209 . Retrieved 2020-06-30.
  28. ↑ National Research Council (2000). Marine mammals and low-frequency sound: Progress since 1994. Washington, D.C.: National Academy Press. doi:10.17226/9756. ISBN   978-0-309-06886-4. PMID   25077255.
  29. ↑ Bombosch, A. (2014). "Predictive habitat modelling of humpback (Megaptera novaeangliae) and Antarctic minke (Balaenoptera bonaerensis) whales in the Southern Ocean as a planning tool for seismic surveys". Deep-Sea Research Part I: Oceanographic Research Papers. 91: 101–114. Bibcode:2014DSRI...91..101B. doi: 10.1016/j.dsr.2014.05.017 .
  30. ↑ National Research Council (2003). Ocean Noise and Marine Mammals. National Academies Press. ISBN   978-0-309-08536-6 . Retrieved 2015-01-25.

Further reading

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.