DOCSLIB.ORG

Low-Frequency Sound Attenuation in the Deep Ocean R

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Low-Frequency Sound Attenuation in the Deep Ocean R Low-Frequency Sound Attenuation in the Deep Ocean R. J. Urick Citation: The Journal of the Acoustical Society of America 35, 1413 (1963); doi: 10.1121/1.1918705 View online: https://doi.org/10.1121/1.1918705 View Table of Contents: http://asa.scitation.org/toc/jas/35/9 Published by the Acoustical Society of America Articles you may be interested in Ray and Wave Invariants for SOFAR Channel Propagation The Journal of the Acoustical Society of America 46, 1259 (1969); 10.1121/1.1911850 Low-frequency ambient noise in the deep sound channel—The missing component The Journal of the Acoustical Society of America 69, 1009 (1981); 10.1121/1.385680 Transmission Characteristics of the SOFAR Channel The Journal of the Acoustical Society of America 48, 767 (1970); 10.1121/1.1912201 Sound channel in an exponentially stratified ocean, with application to SOFAR The Journal of the Acoustical Society of America 55, 220 (1974); 10.1121/1.1914492 Deep-Ocean Sound Attenuation in the Sub- and Low-Kilocycle-per-Second Region The Journal of the Acoustical Society of America 38, 648 (1965); 10.1121/1.1909768 Analytic Description of the Low-Frequency Attenuation Coefficient The Journal of the Acoustical Society of America 42, 270 (1967); 10.1121/1.1910566 THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA VOLUME 35, NUMBER 9 SEPTEMBER 1963 Low-Frequency Sound Attenuation in the Deep Ocean R. J. URICK U.S. Naval OrdnanceLaboratory, White Oak, Silver Spring, Maryland (Received24 May 1963) Signalsreceived from Sofar bombsdropped from an aircraft eastwardfrom Bermuda have beenstudied quantitatively. The energydensity of the signalsreceived at Bermuda, measuredin variousbands between 20 and 1600cps, can be accountedfor by cylindricalspreading beyond a "transitionrange" predicted approxi- mately by simpleconsiderations, plus an attenuationcoefficient in dB per megayardgiven by the linear expression1.5+8.2 f, wheref is the frequencyin kc/sec.At frequenciesbelow 1 kc/sec,this attenuationis far in excessof that which would be producedby absorptionalone. At very low frequenciesthe excessat- tenuation is postulatedto be due to the failure of the Sofar soundchannel to act as an acoustictrap. At frequenciesfrom about 50 to 500 cps, quantitative evidenceis presentedto indicate that the dominant attenuationprocess is scatteringby index-of-refractioninhomogeneities deep in the sea.Other characteristics of Sofar-transmitted signalsare described. INTRODUCTION tention.4.* However, the amplitude, duration, and spectralcharacteristics of Sofar signalshave not been Nsurfaces,the deep the ocean, attenuation farfrom of soundeffects at of frequenciesthe bounding be- studied extensively from a quantitativeviewpoint, even low 1 kc/sec is known to be of the order of only a small though these characteristicsare of dominant interest fraction of a decibelper mile. For example,the formula for long-rangeacoustic communication in the deep sea. This paperdescribes the resultsof a seriesof measure- a=0.033f• (a in dB per kiloyard,f in kc/sec)proposed ments made across the Atlantic Ocean between by Sheehyand Halley,• as a fit to their measurements, wouldindicate a coefficientof only 0.033dB per kiloyard Bermudaand the United Kingdom. The spreadinglaw and attenuation coefficient for this series of shots and at 1 kc/sec, with smaller values at lower frequencies. Measurementsof valuesas low as theserequire propa- the lossproduced by the Mid-Atlantic Ridge are de- gation paths that are measuredin hundredsof miles, scribed,and processesare postulatedto accountfor under conditionswhere reflection and scattering from the excessattenuation over that due to absorptionat the sea surface and sea bed are not involved. This low frequencies. implies,in turn, the useof the Sofarchannel for long- MEASUREMENT PROCEDURE distancepropagation, since the requiredpath lengths and freedom from boundaries cannot otherwise be ob- StandardNavy Sofar signals,containing the equiva- tained.In addition,the useof explosivesis dictatedby lent of 4 pounds of TNT, were dropped on a pre- the needfor high acousticsource levels. assignedtime scheduleby an aircraft as it flew between The existenceof a soundchannel in the deep seawas Bermuda and Great Britain via the Azores during predicted and demonstratedby Ewing and Worzel2 June1962. The locationof the dropsis shownin Fig. 1. about 20 yearsago. Named for its usefor soundfixing The maximumrange, from Bermudato the furthermost and ranging,it has receivedattention as a meansof drop,was 2516 miles. At eachlocation a pair of signals location of downed aviators and, more recently, of set to detonate at depths of 1500 and 3500 ft was missileimpacts? In consequence,the travel times for droppedalong with a sonobuoyfor observingthe Sofarchannel propagation have receivedabundant at- instant of detonation aboard the aircraft. At the Bermudaend, recordingswere made with hydrophones •M. J. Sheehyand R. Halley, J. Acoust.Soc. Am. 29, 464 4 R. A. Frosch,M. Klerer, and L. Tyson,J. Acoust.Soc. Am. (1957). 33, 1804 (1961). 2 M. Ewing and J. L. Worzel, Geol. Soc.Am. Mem. 27 (1948). 5 G. M. Bryan, M. Truchan,and J. Ewing,J. Acoust.Soc. Am. 3H. H. Baker, Bell Lab. Record39, No. 6, 195 (June 1961). 35, 273 (1963). 1413 1414 R. J. URICK Fro. 1. Location of Sofar bomb drops. at variousdepths; however, only the data from a As a result,Sofar signals received at a greatdistance hydrophoneat 3900ft, in water14 000 ft deep,are havea typicalenvelope that showsa gradualbuildup describedin thispaper. The taperecordings were later and reaches a sudden climax at the instant that the analyzedin theconventional way by playingback into axiallytraveling energy arrives. This abruptending is bandpassfilters, squaring, and integrating to obtainthe the characteristicthat makes them useful for triangu- energydensity of the receivedsignals in the various lation purposes. filter bands. Alongthe path of the dropsshown in Fig. 1, the transmission of sound in the Sofar channel is inter- SOFAR CHANNEL AND SIGNAL ENVELOPES ruptedby the Mid-AtlanticRidge, which forms an The Sofar soundchannel is an internal acousticduct acousticbarrier for deeppropagation across the Atlantic havingits axis, or depth of minimum velocity, at depths Ocean.Bathymetric charts ø shownumerous places in rangingfrom about 5000 ft in thetropics to nearthe thevicinity of the acousticpath where the crestsof the surfacein highlatitudes. Its existencedepends upon Ridgepierce the depthof the Sofaraxis and thuscut the fact that the velocityof soundincreases with both off near-axialrays carrying the principalportion of the transmittedenergy. The attenuatingeffect of the Ridge temperatureand pressure; at shallow depths, where the will be evident in the results to follow; in spite of it, temperaturedecreases with depth, the temperature effect is dominant and the velocity decreases;at great signalswere received 5 to 10 dB abovenoise at the depthswhere the sea is nearlyisothermal, the pressure maximum range (Drop 29), althoughthe dropsjust effectcauses the velocityto increaseagain. Figure 2, beyondthe Ridge(Drops 20, 21) appearto havebeen taken from the now-classicpaper on the subjectby cut off by the shadowingeffect of the crestsand were not received at Bermuda. Ewingand Worzel, •'shows a typicalvelocity profile in The sound-velocitystructure along the line of drops midlatit.udes•together with a ray diagramfor a source on theaais. Ray pathsnear the axis carry most of the 6 ChartsBC 0307N, BC 0308N, publishedby the U.S. Navy .energy•.n,.• .a.r,e •oc[ated with the longest travel time. OceanographicOffice. SOUND ATTENUATION IN THE DEEP OCEAN 1415 DO0 FIG. 2. Ray diagramof the Sofar soundchannel. [Reproduced from Ewing and Worzel.2-] was estimated from velocity data provided by the been done by Brekhovskikh,7 that for both sourceand National OceanographicData Center. Figure 3 is a receiver on the axis of a sound channel the difference in velocity contour cross section drawn from N.O.D.C. travel times along the axial ray and along the ray hydrographicdata for the month of Juneat stationsin leavingthe sourceat an angle00 is tOo2/6,where t is the the vicinity of the drop path. The feature most worthy axial travel time. The straightline in Fig. 5 showsthis of note is the decreasingvelocity at shallow depths calculatedduration for 00-12.2 ø for the ray of maxi- toward the right, reflectingthe lower surfacetempera- mum inclination propagating without reflection at tures toward the northeast along the drop path. How- either the seasurface or seabed. The agreementis sur- ever, the depth of the Sofar axis is approximatelycon- prising, consideringthat the Sofar channelhas by no stant, although at the northeasterlyend its depth is means the linear gradient on either side of its axis re- made uncertainby the occurrenceof nearly isovelocity quired for this approximation.The absenceof a clear conditions. beginningto the receivedsignal is perhapsdue to the Figure 4 showssignal envelopes in the band 50-150 contributionby rays which leave the sourcebeyond cpsfor a shotat 3500 ft as receivedby the hydrophone 12.2ø and which sufferrepeated reflection at either or at 3900 ft at Bermuda. The vertical scale shows the both seaboundaries. Beyond the Ridgeat abouta range band level in decibelsrelative to the intensity of a plane of 1800 miles, the durations based on the above cri- wave of 1 dyn/cm2 rms pressure.The envelopesexhibit terionare muchshorter because the early portion of the the expectedlengthening and weakening with increasing signalsare buried in noise,and becausethe near-axial
Load more

Recommended publications
  • Lagrangian Measurement of Subsurface Poleward Flow Between 38 Degrees N and 43 Degrees N Along the West Coast of the United States During Summer, 1993
    CORE Metadata, citation and similar papers at core.ac.uk Provided by Calhoun, Institutional Archive of the Naval Postgraduate School Calhoun: The NPS Institutional Archive Faculty and Researcher Publications Faculty and Researcher Publications 1996-09-01 Lagrangian Measurement of subsurface poleward Flow between 38 degrees N and 43 degrees N along the West Coast of the United States during Summer, 1993 Collins, Curtis A. Geophysical Research Letters, Vol. 23, No. 18, pp. 2461-2464, September 1, 1996 http://hdl.handle.net/10945/45730 GEOPHYSICAL RESEARCH LETTERS, VOL. 23, NO. 18, PAGES 2461-2464, SEPTEMBER 1, 1996 Lagrangian Measurement of subsurface poleward Flow between 38øN and 43øN along the West Coast of the United States during Summer, 1993 CurtisA. Collins,Newell Garfield, Robert G. Paquette,and Everett Carter 1 Departmentof Oceanography,Naval Postgraduate School, Monterey, California Abstract. SubsurfaceLagrangian measurementsat about Undercurrentalong the coastsof California and Oregon. We 140 m showedthat the pathof the CaliforniaUndercurrent lay are using quasi-isobaric(float depth controlled primarily by next to the continentalslope betweenSan Francisco(37.80N) the pressureeffect on density)RAFOS floats (Rossby et al., and St. GeorgeReef (41.8øN) duringmid-summer 1993. The 1986) to make these measurements. A RAFOS float consists meanspeed along this 500 km pathwas 8 cms-1. Theflow at of a hydrophonemounted in a glasstube that is about2 meters this depth was not disturbedby upwelling centersat Point long. These hydrophonesreceive signals from three sound Reyesor CapeMendocino. Restfits also demonstratethe abil- sources that were moored 400 km offshore between 34.3øN and ity to acousticallytrack floats located well above the sound 40.4øN.The sound sources emit 15 W, 80 s signalsa•t 260 Hz channelaxis along the California coast.
    [Show full text]
  • University Microfilms, Inc., Ann Arbor, Michigan the SYNTHESIS of POINT DATA
    This dissertation has been microfilmed exactly as received 68-16,949 JOHNSON, Rockne Hart, 1930- THE SYNTHESIS OF POINT DATA AND PATH DATA IN ESTIMATING SOFAR SPEED. University of Hawaii, Ph.D., 1968 Geophysics University Microfilms, Inc., Ann Arbor, Michigan THE SYNTHESIS OF POINT DATA AND PATH DATA IN ESTIMATING SOFAR SPEED A DISSERTATION SUBMITTED TO THE GRADUATE DIVISION OF THE UNIVERSITY OF HAWAII IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN GEOSCIENCES June 1968 By Rockne Hart Johnson Dissertation Committee: William M. Adams, Chairman Doak C. Cox George H. Sutton George P. Woollard Klaus Wyrtki ii P~F~E Geophysical interest in the deep ocean sound (sofar) channel centers on its use as a tool for the detection and location of remote events. Its potential application to oceanography may lie in the monitoring of variations of physical properties averaged over long paths by sofar travel-time measurements. As the accuracy of computed event locations is generally dependent on the accuracy of travel-time calculations, the spatial and temporal variation of sofar speed is a matter of fundamental interest. The author's interest in this problem has grown out of a practical need for such information for application to the problem of locating the sources of earthquake I waves and submarine volcanic sounds. Although an exten­ sive body of sound-speed data is available from hydrographic casts, considerably more precise measurements can be made of explosion travel times over long paths. This dissertation develops a novel procedure for analytically combining these two types of data to produce a functional description of the spatial variation of safar speed.
    [Show full text]
  • Overview of the Impacts of Anthropogenic Underwater Sound in the Marine Environment
    Overview of the impacts of anthropogenic underwater sound in the marine environment Biodiversity Series 2009 Overview of the impacts of anthropogenic underwater sound in the marine environment OSPAR Convention Convention OSPAR The Convention for the Protection of the La Convention pour la protection du milieu Marine Environment of the North-East Atlantic marin de l'Atlantique du Nord-Est, dite (the “OSPAR Convention”) was opened for Convention OSPAR, a été ouverte à la signature at the Ministerial Meeting of the signature à la réunion ministérielle des former Oslo and Paris Commissions in Paris anciennes Commissions d'Oslo et de Paris, on 22 September 1992. The Convention à Paris le 22 septembre 1992. La Convention entered into force on 25 March 1998. It has est entrée en vigueur le 25 mars 1998. been ratified by Belgium, Denmark, Finland, La Convention a été ratifiée par l'Allemagne, France, Germany, Iceland, Ireland, la Belgique, le Danemark, la Finlande, Luxembourg, Netherlands, Norway, Portugal, la France, l’Irlande, l’Islande, le Luxembourg, Sweden, Switzerland and the United Kingdom la Norvège, les Pays-Bas, le Portugal, and approved by the European Community le Royaume-Uni de Grande Bretagne and Spain. et d’Irlande du Nord, la Suède et la Suisse et approuvée par la Communauté européenne et l’Espagne. 2 OSPAR Commission, 2009 Acknowledgements Author list (in alphabetical order) Thomas Götz Scottish Oceans Institute, East Sands University of St Andrews St Andrews, Fife KY16 8LB [email protected] Module 2, 8 Gordon Hastie SMRU Limited New Technology Centre North Haugh St Andrews, Fife KY16 9SR [email protected] Module 2, 8 Leila T.
    [Show full text]
  • Acceleration in Acoustic Wave Propagation Modelling Using Openacc/Openmp and Its Hybrid for the Global Monitoring System
    Acceleration in Acoustic Wave Propagation Modelling using OpenACC/OpenMP and its hybrid for the Global Monitoring System Noriyuki Kushida*1, Ying-Tsong Lin*2, Peter Nielsen*1, and Ronan Le Bras*1 *1 CTBTO Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization Provisional Technical Secretariat *2 Woods Hole Oceanographic Institution, USA Disclaimer: The views expressed herein are those of the author(s) and do not necessarily reflect the views of the CTBT Preparatory Commission. Background (Who we are) The CTBT (Comprehensive Nuclear-Test-Ban Treaty) bans all types of nuclear explosions. CTBTO operates a worldwide monitoring system to catch the signs of nuclear explosions with four technologies: Seismic Infrasound Hydroacoustic Radionuclide Atmospheric explosion Underground explosion Underwater explosion 2 Background (Underwater event and Hydroacoustic observation) ● Hydroacoustic: acoustic waves through the Ocean Seismometer Hydrophone Phase conversion Underwater explosion ● A big explosion in the Ocean can generate a sound wave ● We can catch such sounds with ○ microphones in the Ocean (hydrophone) ○ seismometers on the coast Photo/Video from CTBTO Website Background (Hydroacoustic stations in CTBTO) ● “H” icone: Hydrophone (H-phase). 6 stations ● “T” icone: Seismometer (T-phase). 4 stations ● Hydroacoustic waves can travel very long distances ○ Complex phenomena can be involved ● Seismic stations; 170 (50 primary + 120 auxiliary) to cover the globe An example: Argentinian submarine ARA San Juan 1/3 Last Contact
    [Show full text]
  • Oceanography
    Oceanography Course Outline Unit One Introduction to Oceanography 7 days Unit Two Structure of the Earth & Modern Navigational Techniques 7 days Unit Three Plate Tectonics 7 days Unit Four The Sea Floor and Its Sediments 9 days Unit Five Physical and Chemical Properties of Water 7 days Unit Six The Atmosphere and Circulation 5 days Unit Seven Ocean Structure and Currents 7 days Unit Eight Waves 5 days Unit Nine Tides 5 days Unit Ten Coasts, Beaches & Estuaries 12 days Unit Eleven Marine Biology 14 days School-wide Academic Expectations Addressed in Oceanography: Problem Solving Critical Thinking Collaboration Writing Skills School-wide Social and Civic Expectations Addressed in Oceanography: Honesty Responsibility Respect Safety Common Core Standards Addressed in Oceanography: Reading Standard for Science Literacy (RST): 2, 3, 4, 7, 8, 9 Writing Standards for Science Literacy (WHST): 1, 2, 4, 9 NGSS Standards Addressed in Oceanography: TBD Unit 1: Introduction to Oceanography Introduction: Oceanography is a multidisciplinary field in which geology, chemistry, physics, and biology are incorporated. This unit focuses on the historical perspective - the contributions of various individuals/groups and the advancement of technology in the development of our understanding of the oceans. CT State Standard(s): Energy in the Earth System. Common Core Standard(s): · Reading Standard for Science Literacy (RST): 2, 3, 4, 7, 8, 9 · Writing Standards for Science Literacy (WHST): 1, 2, 4, 9 School-wide Academic Expectations Addresses in this
    [Show full text]
  • WILLIAM MAURICE EWING May 12, 1906-May 4, 1974
    NATIONAL ACADEMY OF SCIENCES WILLIAM MAURICE Ew ING 1906—1974 A Biographical Memoir by ED W A R D C . B ULLARD Any opinions expressed in this memoir are those of the author(s) and do not necessarily reflect the views of the National Academy of Sciences. Biographical Memoir COPYRIGHT 1980 NATIONAL ACADEMY OF SCIENCES WASHINGTON D.C. WILLIAM MAURICE EWING May 12, 1906-May 4, 1974 BY EDWARD C. BULLARD* CHILDHOOD, 1906-1922 ILLIAM MAURICE EWING was born on May 12, 1906 in W Lockney, a town of about 1,200 inhabitants in the Texas panhandle. He rarely used the name William and was always known as Maurice. His paternal great-grandparents moved from Kentucky to Livingston County, Missouri, at some date before 1850. Their son John Andrew Ewing, Maurice's grandfather, fought for the Confederacy in the Civil War; while in the army he met two brothers whose family had also come from Kentucky to Missouri before 1850 and were living in De Kalb County. Shortly after the war he married their sister Martha Ann Robinson. Their son Floyd Ford Ewing, Maurice's father, was born in Clarkdale, Mis- souri, in 1879. In 1889 the family followed the pattern of the times and moved west to Lockney, Texas. Floyd Ewing was a gentle, handsome man with a liking for literature and music, whom fate had cast in the unsuitable roles of cowhand, dryland farmer, and dealer in hardware and farm implements. Since he kept his farm through the *This memoir is a corrected and slightly amplified version of one published by the Royal Society in their Biographical Memoirs (21:269-311, 1975).
    [Show full text]
  • Long-Term Autonomous Hydrophones for Large-Scale Hydroacoustic Monitoring of the Oceans Jean-François D’Eu, Jean-Yves Royer, Julie Perrot
    Long-term autonomous hydrophones for large-scale hydroacoustic monitoring of the oceans Jean-François d’Eu, Jean-Yves Royer, Julie Perrot To cite this version: Jean-François d’Eu, Jean-Yves Royer, Julie Perrot. Long-term autonomous hydrophones for large- scale hydroacoustic monitoring of the oceans. Yeosu 2012, May 2012, Yeosu, North Korea. pp.1-6, 10.1109/OCEANS-Yeosu.2012.6263519. insu-00817948 HAL Id: insu-00817948 https://hal-insu.archives-ouvertes.fr/insu-00817948 Submitted on 22 May 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Long-term autonomous hydrophones for large-scale hydroacoustic monitoring of the oceans Jean-François D’Eu, Jean-Yves Royer, Julie Perrot Laboratoire Domaines Océaniques CNRS and University of Brest Plouzané, France [email protected] Abstract—We have developed a set of long-term autonomous hydrophones dedicated to long-term monitoring of low-frequency A. Monitoring ocean seismicity at a broad scale sounds in the ocean (<120Hz). Deploying arrays of such Seismicity in the ocean is usually recorded with the help of hydrophones (at least 4 instruments) proves a very efficient seismometers, such as Ocean Bottom Seismometers (OBS), approach to monitor acoustic events of geological origin placed in the proximity of active areas.
    [Show full text]
  • Sound Speed in the Mediterranean Sea: an Analysis from a Climatological Data Set
    c Annales Geophysicae (2003) 21: 833–846 European Geosciences Union 2003 Annales Geophysicae Sound speed in the Mediterranean Sea: an analysis from a climatological data set S. Salon1, A. Crise1, P. Picco2, E. de Marinis3, and O. Gasparini3 1Istituto Nazionale di Oceanografia e di Geofisica Sperimentale–OGS, Borgo Grotta Gigante 42/C, I-34010 Sgonico–Trieste, Italy 2Centro Ricerche Ambiente Marino, CRAM-ENEA, S.Teresa, Localita` Pozzuolo di Lerici, I-19100, La Spezia, Italy 3DUNE s.r.l., Via Tracia 4, I-00183 Roma, Italy Received: 9 April 2002 – Revised: 26 August 2002 – Accepted: 18 September 2002 Abstract. This paper presents an analysis of sound speed served in the northwestern Mediterranean (Send et al., 1995) distribution in the Mediterranean Sea based on climatologi- and in the Greenland Sea (Pawlowicz et al., 1995; Morawitz cal temperature and salinity data. In the upper layers, prop- et al., 1996). Ocean acoustic tomography has also proved to agation is characterised by upward refraction in winter and be a methodology for the observation of currents and internal an acoustic channel in summer. The seasonal cycle of the tides (Shang and Wang, 1994; Demoulin et al., 1997). These Mediterranean and the presence of gyres and fronts create a successful applications propose ocean tomography as a tool wide range of spatial and temporal variabilities, with rele- for large-scale monitoring of the oceans in the frame of the vant differences between the western and eastern basins. It development of Global Oceans Observing Systems (GOOS). is shown that the analysis of a climatological data set can In spite of this growing interest in acoustic inversion, an help in defining regions suitable for successful monitoring by analysis of the sound speed field in the Mediterranean Sea is means of acoustic tomography.
    [Show full text]
  • Underwater Acoustics - Gee-Pinn James Too
    OCEANOGRAPHY – Vol.III - Underwater Acoustics - Gee-Pinn James Too UNDERWATER ACOUSTICS Gee-Pinn James Too National Cheng Kung University, Taiwan Keywords: Underwater Acoustics, Underwater Communication, Underwater Detection, Sound Velocity Profiles, Surface Duct, Shadow Zone, SOFAR (Deep Sea) Channel, Acoustic Ray Model, Normal Mode Model, PE (Parabolic Wave Equation) Models, Temperature, Pressure, and Salinity. Contents 1. An Acoustical View of Oceanography 2. The History of Research on Ocean Acoustics 3. Measurement of Speed of Sound 3.1. The Sound Speed Profile 3.2. Propagation Theory 3.3. Applications of Underwater Acoustics 4. Other Applications Bibliography Biographical Sketch Summary Underwater acoustics is an important science with significant practical application, especially for the application in ocean. Electro-magnetic waves, which are strongly absorbed by water, have their limits in propagation range in water. Therefore, acoustic waves play an important role on the navigation, underwater communication, underwater detection, and investigation in ocean research. The ocean is an inhomogeneous medium with various sound velocity profiles that vary with depth because of changes in temperature, hydrostatic pressure and salinity. Due to these sound velocity profiles, acoustic wave propagation in ocean results in several interesting phenomena such as surface duct, shadow zone, SOFAR (deep sea) channel, etc. These phenomena all have practical application in underwater communication and detection. Theoretical models and their numerical algorithms for wave propagation are developedUNESCO to describe the complicated ocean– phenomenaEOLSS of wave propagation. Some of these models, such as: acoustic ray model, normal mode model, PE (parabolic wave equation) models are described in this section. SAMPLE CHAPTERS Sonar equations comprise a group of parameters, which considers the phenomena and effects of the underwater sound.
    [Show full text]
  • Indian Ocean Hydroacoustic Wave Propagation Characteristics
    INDIAN OCEAN HYDROACOUSTIC WAVE PROPAGATION CHARACTERISTICS Pierre-Franck Piserchia, Pierre-Mathieu Dordain CEA/DIF – Département Anlayse, Surveillance, Environnement, France Sponsor Commissariat à l’Energie Atomique (CEA), France ABSTRACT The channeling efficiency of the Deep Sound Channel (often referred as the Sofar channel) allows long range propagation of hydroacoustic waves over a few thousands of kilometers. Strong T-waves, referring to a third arrival on seismic waves, are commonly observed on underwater receivers (hydrophones stations) and on coastal receivers (T-phase stations), when an oceanic earthquake or an underwater explosion occurs, even for small events. Consequently, to insure the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT), the hydroacoustic network of the International Monitoring System (IMS) uses five T-phase stations and six hydrophones. At the end of 2001, three hydrophone stations -HA1 at Cape Leeuwin, HA4 at Crozet, and HA8 at Diego Garcia will continuously send their data to the IMS. These data will also be available at National Data Centers. Then, using these data it will be possible 1) to refine the network detection capability 2) to estimate the network localization precision and 3) to estimate the transmission loss of the hydroacoustic propagation and the hydroacoustic-to-seismic conversion at the T-phase stations. To prepare this evaluation, we are studying the underwater propagation in the region of the Indian Ocean and in the South Atlantic Ocean using modeling approaches. The first part of this paper gives a general view of the variation of the bathymetry, the sound speed propagation and the Sofar channel axis in the Indian Ocean.
    [Show full text]
  • Some Effects of Large-Scale Oceanography on Acoustic Propagation
    GUTHRIE~ SHAFFER & FITZGERALD: Effeats of oaeanography on aaoustia propagation SOME EFFECTS OF LARGE SCALE OCEANOGRAPHY ON ACOUSTIC PROPAGATION by A.N. Guthrie, J.D. Shaffer, and R.M, Fitzgerald Naval Research Laboratory, Washington, DC 20375 ABSTRACT A propagation experiment was conducted along a great circle track in the North American Basin, beginning at a point 400 km north of Antigua, W.I. and ending at the Grand Banks of Newfoundland. Shallow explosive sources were detonated at half hour intervals and shallow-13.89 and 111.1 Hz cw sources were operated continuously. The acoustic fields were detected by a deep sound channel hydrophone located near Antigua. The shot signatures were aligned in time and range forming a pattern which was dependent on and could be inter- preted in terms of large-scale oceanography, Major features of the transmission loss curves for the two continuous wave sources are similarly interpretable in terms ,of averaged oceanographic parameters. SACLANTCEN CP-17 26-1 GUTHRIE~ SHAFFER & FITZGERALD: Effects of oceanography on acoustic propagation INTRODUCTION Ocean acoustic modeling for prediction of propagation of sound in the ocean is a most complicated problem. Transmission from a source to a receiver is a multipath process with a relatively large number of acoustic paths. In traveling these paths the signals are modified in complex ways by interaction \oJi th the ocean surface and bottom, and with the sound speed gradients in the water. Further modifications result from loss of energy by absorption and from scatt~ring by various agen~s encountered along the paths. The =Qcifications that result depend on the signal frequency, the ~razing angles at the surfaces, and a n~~er of other parameters.
    [Show full text]
  • A Global Network of Hydroacoustic Stations for Monitoring.…
    A GLOBAL NETWORK OF HYDROACOUSTIC STATIONS FOR MONITORING THE COMPREHENSIVE NUCLEAR-TEST-BAN TREATY PACS: 43.10.Qs Marta Galindo Arranz Hydroacoustic Officer, Hydroacoustic Monitoring, IMS Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) Vienna Austria E-mail: [email protected] ABSTRACT Hydroacoustics is one of the four monitoring technologies of the International Monitoring System (IMS) established under the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The hydroacoustic network, designed to monitor the major world oceans, contains eleven stations located with an emphasis on the vast ocean areas of the Southern Hemisphere. Two different sensing techniques are employed; hydrophone sensors, which effectively cover large ocean areas, but are quite complex and expensive, and seismic detectors on small islands which are less effective, but considerably simpler and cheaper. The hydroacoustic stations transmit data in real time via satellite to the International Data Centre (IDC) located in Vienna, Austria. The IDC analyses the hydroacoustic data in combination with the other three technologies to produce bulletins of detected events for the States Party to the T RESUMEN El Tratado de Prohibición Completa de los Ensayos Nucleares (TPCE) es una piedra angular del régimen internacional para la no proliferación de armas nucleares y la base para perseguir el desarme nuclear. La Comisión Preparatoria de la Organización del Tratado de Prohibición Completa de los Ensayos Nucleares (OTPCE), ubicada en Viena, es una organización internacional establecida por los Estados Signatarios del Tratado del 19 de noviembre de 1996. El principal objetivo de la Comisión es el establecimiento de 337 instalaciones que forman el Sistema de Vigilancia Internacional y el Centro Internacional de Datos.
    [Show full text]