Downloaded from orbit.dtu.dk on: Dec 17, 2017 Comparison of procedures for determination of acoustic nonlinearity of some inhomogeneous materials Jensen, Leif Bjørnø Published in: Acoustical Society of America. Journal Link to article, DOI: 10.1121/1.2020879 Publication date: 1983 Document Version Publisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Jensen, L. B. (1983). Comparison of procedures for determination of acoustic nonlinearity of some inhomogeneous materials. Acoustical Society of America. Journal, 74(S1), S27-S27. DOI: 10.1121/1.2020879 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. PROGRAM OF The 106thMeeting of the AcousticalSociety of America Town and CountryHotel © San Diego, California © 7-11 November1983 TUESDAY MORNING, 8 NOVEMBER 1983 SENATE/COMMITTEEROOMS, 8:30 A.M. TO 12:10P.M. Session A. Underwater Acoustics: Arctic Acoustics I William Mosely,Chairman Naval ResearchLaboratory, Washington, DC 20375 Chairman's Introductions8:30 Invited Papers 8:35 A1. Bottom-interactingacoustic signais in the Arctic channel:Long-range propagation. Henry W. Kutschale andTai Lee(Lamont-Doherty Geological Observatory of ColumbiaUniversity, Palisades, NY 10964) Hydroacousticsignals from underwaterexplosions that havepropagated over the Arctic abyssalplains commonlydisplay marked frequency dispersion in pulsesthat arebottom-interacting and that arriveafter the $OFAR signal.In theinfrasonic band of 2 to 20 Hz, the temporaldispersion for eachpulse that has interacted withthe fiat bottom of theplain can be nearly as strong as that observed in the$OFAR signalfor thefirst mode. However,the bottom-interactingpulses correspond to a coherentsummation of manyhigher-order normal modesin a channelbounded above by theocean surface and below by theupper 400 m of thebottom sediments, wherethe velocityincreases with depth.Using normal-mode theory and the Multiple ScatteringPulse Fast Field Program(MSPFFP), we haveanalyzed the dispersionand pulseshapes and havederived the acoustic propertiesof thebottom in the Pole,Barents, and Mendeleyev Abyssal Plains. The principalproperties of the bottomcontrolling the propagationare compressionalvelocity, density, and attenuation.In contrast,the ice layerhas a negligibleeffect on the dispersionof the observedwaves. The effecton pulsecompression of this frequencydispersion of the bottom-interactingsignals was simulated numerically, using predistorted wave- formsmatched to thedispersion of the SOFAR channelat specifiedranges. 9:00 A2. Ambientnoi•e in thecentral Arctic Ocean. Ira Dyer (Departmentof OceanEngineering, Massachusetts Instituteof Technology,Cambridge, MA 02139) Underwaterambient noise has been measured in thecentral Arctic Ocean on three separate occasions with theuse of a horizontaland a verticalarray. These data help to identifyvarious noise mechanisms. Of principal interestis noise caused by variousice cracking events which depend upon stress levels in theice and which seem to havevarying temporal and spectral characteristics. I review these mechanisms and show how the data relate to them.While spatial analyses have been carried out only at verylow frequencies, spectral analyses cover the rangefrom I to 10000 Hz. In this frequencyrange noise mechanisms other than packice are sometimes important,such as wind-generated noise and earthquakenoise. [Work supportedby ONR.] 9:25 A3. Seismic/acousticpropagation in the Arctic Ocean.Arthur H Baggeroerand GregoryL. Duckworth (Departmentsof Oceanand ElectricalEngineering, Massachusetts Institute of Technology,Cambridge, MA 02139} During the FRAM II and FRAM IV experimentsin the Pole AbyssalPlain and the BarentsAbyssal Plain of the Arctic Ocean24 channelhydrophone arrays approximately I km X I km in extentwere used to record digitallyboth seismic refraction and long-range acoustic propagation data. From these data the velocity versus depthfunction for the seismic structure along the FRAM II andFRAM IV drift trackswere estimated by high- resolutionvelocity spectral analysis and tau-slownessmigration methods. These indicate oceanic layers 2 and 3, but they are relatively thin. These techniqueswere also usedto identify internal and surface-reflected Sl J. Acoust.Soc. Am.Suppl. 1, Vol. 74, Fall 1983 108thMeeting: Acoustical Society of America multipathsas well as converted shear paths to obtaina detailedcharacterization of the seismic propagation. Thelong-range acoustic signals contained strong modal components and bottom interacting ones. Velocity spectraand autoregressive algorithms resolved the dispersive properties ofthe phase and group velocity of each mode.These were usedto estimatethe water columnsound velocity profile with an inversionalgorithm. DuringFRAM II thebottom interactions lasted up to 80s long and contained as much energy as the low-order modesat low frequencies.These signals were used to estimatethe shallowvelocity versus depth structure. DuringFRAM IV thedispersion characteristics ofthe low-order modes changed slightly. In contrast,virtually no bottom-interactingenergy was observed suggesting strong scattering of the deeppaths by an intervening midoceanicridge. [Work supportedby ONR Arctic ProgramOffice.] A4. TRISTEN/FRAM IV ew spatial eoberenceand temporal stability. F. R. DiNspoll, R. Nielsen, D. Potter(Naval UnderwaterSystems Center, New London,CT 06320),and P. L. Stocklin(Analysis and Technology,Inc., N. Stonington,CT 06359) The TRISTEN-82/FRAM IV experimentwas a multifacetedexperiment investigating acoustics in the Arctic. This paper focuseson the spatial coherenceand temporal (frequency)stability of acousticsignals transmittedand receivedbetween fixed ice camps separated by approximately130 nmi. A high-powered,low- frequency(NUSC HLF-3 Arctic)hydroaroustic source transmitted stable cw tonesof I h or moreat various frequenciesfrom 5 to 200Hz duringApril 1982.These signals were received on an X-shapedarray having an apertureof 1200m on eachleg. The armywas operated by theMassachusetts Institute of Technologyand the Wood Hole OceanographicInstitute. The spatialcoherence, both broadsideand end-fireto the sourcewere foundfrom normalizedsensor pair crosscorrelation, corrected for signal-to-noiseratio. Total and 3-rib down receivedsignal bandwidths were found using complex demodulation and FFF with a resolutionto a fractionof mHz, followedby cumulativeenergy analysis in the frequencydomain. The experimentalsetup data, analysis procedures,and resultswill be presented.[Work sponsoredby the Officeof Naval Research,Code 425-AR.] 10:15 AS.Arctic data collection the easy way--Data buoys.Beanmont M. Buck(Polar Research Laboratory, Inc., 123 SantaBarbara Street, Santa Barbara, CA 93101) This paperpresents a reviewof developmentaland operationaluse of Arctic data buoys.There are many problemsinvolved with aircraftand icebreakerlogistics for scientificsupport in the Arctic. Mannedresearch stationson seaice are expensive,self-contaminating in termsof acousticand electromagneticnoise, and generallylimited to a 40- to 50-dayperiod in thespringtime. Autonomous data buoys, on the other hand, do not sufferthose limitations. These devices can be installedby parsdrop,aircraft ice-landing,submarine, or ice- breakerin almostany geographic area of the ArcticOcean, peripheral seas, and marginal sea ice zones to collect andreport data over all seasons.There are restrictions, of course,as to what can be accomplished automatically withina smallbuoy hull, andalmost all Arctic buoys,so far, havebeen mechanically passive. Recent advances in low-powermicroprocessors and memories enable considerable increases in theextensive in-buoy processing neededfor data compression to aceomodate the limited capacities of polarorbiting scientific satellites. [Work supportedby U.S. Navy andNOAA.] ContributedPapers 10:40 A my-theoreticmodel is advancedto describethe averagereverbera- tion intensitieswithin an Arctic channelbounded by a pack-icesurface A6. Normal mode and ray equivalencein the Arctic sound channel. and an upward-refractingsound-speed profile in the presenceof pressure RobertH. Mellen {B-K Dynamics,Inc., 247 ShawStreet, New London, ridgescattering. The surfaceis assumedrandom and a phenomenological • 06320) modelbased on Kirchoff assumptionsin the high-frequencylimit is de- Effectsof upwardrefraction combined with scatteringby the rough rived.Relevant parameters are estimated from data supplied by Chapman iceinterface result in a dispersivesound channel capable of propagating and Scottusing a curve-fitroutine. Ridges are modeledas inverted cones, only very low frequenciesto long range.Because only a few modesare the surfacesof whichare also assumed random. This simplifyinggeomet- involved,normal mode theory is appropriate.However, surface-scatter ric assumptionallows for a highlytractable technique. Forward as