885095933

complicated environment of the Florida Straits. There appcars to be an order and simplicity out to usable ranges. Model results raise ncw questions and suggest new typcs of experiments. [Work supportcd by ONR.]

9:00

6UW2. Wave-front fluctuations in the 1000-km SLICE89 expcriment. S. M. Flattć, T. F. Duda, J. Colosi (Inst. of Marinc Sci., Univ. of Califomia, Santa Cruz, CA 95064), J. Hildebrand, W. Hodgkiss, P. F. Worcester, B. D. Comuelle (Scripps Inst. of Oceanography, Univ. of Califomia, La Jolla, CA 92093), B. M. Howe, J. Mercer, and R. Spindel (Univ. of Washington. Seatlle, WA 98105)

A 1000-km acoustical transmission expcriment has been carried out in the North Pacific in order to quantify long-rangc acoustic fluctuations at pcriods of hours to days, and to measure mcsoscale and intemal-wave sound-speed structure within the source-to-receiver vertical slice. Pseudo-random-$equencc pulses were transmitted by a moored broadband sound source (centcred at 250 Hz) to a moored 3-km vertical array of 50 rcceivers. Data are availablc in the form of approximately 1000 transmisions at 1/h (spanning nine days), with an embedded sequence of another 1000 transmissions at 6/h (spanning 21 h). The multipath arrivals form a elear expected pattem of a single, folded wave front in the earlicr part of the received pulses. Each point on the folded wave front represents a specific ray trajectory through the ocean. Several hundred points are availablc on each of the pulses. Removal of barotropic tides and cquipment-motional fluctuations was carried out by averaging tcchniques, yielding residuals that are dominated by ocean processes such as intemal waves. Time-laggcd and vertically lagged covarianccs of residuals show the temporal and spatial scales of variability within the pulse, which can be related to the behavior of ocean processes. Baroclinic tides and intemal waves are apparent in the record.

Contributed Papers

1962

1962

9:30

6UW3. Relating ocean acoustic ambient noise to the ocean surface dynamics. Robert M. Kennedy (Naval Underwater Syst. Ctr., AUTEC, West Palm Beach, FL 33402-7517)

The acoustical significance of ocean surface dynamics has been doc-umented for years. Motivation for establishing the rcquired causal re-lations between these two physical processes has existed for decades. The goal has eluded investigators because of the complexity of both the acoustic and oceanographic mechanisms involvcd. Significant conlribu-tions have been madę by a progression of laboratory measurements of various spatial scales as reccntly reported [H. Medwtn, J. Acousl. Soc. Am. Suppl. 1 88, SI (1990); L. A. Crum et al., J. Acoust. Soc. Am. Suppl. 1 88, S2 (1990)]. The work discusscd here continues the progression in spatial scales by utilizing a relatively dcep water basin (The Tongue of the Ocean, the Bahamas) in a quasicontrolled environment which madę a broadband measurement (40 to 4000 Hz) of the vertical directional spectrum of the ambient acoustic field. The 1-yr database of directional spectrum is dominated by local (fetch limited) water surface conditions over a wide rangę of environmental conditions. While the exploratory naturę of the experiment limited the amount of supporting meterological and oceanographic measurements madę, the results give dircction to what are the likely independent variables of the expcriment. A discussion of the kcy environmental variables and the consistcncy of the results with existing theories is givcn in the context of the design of a futurę cxperiment to relate the acoustic ambient with ocean surface dynamics.

9:45

6UW4. Ocean acoustics turbulence study (OATS). Louis Goodman, Dianę Szargowicz (Naval Underwater Syst. Ctr., Newport, RI 02841), Stephen Leicher, John Oeschger, and Elcna Balasco (Univ. of Rhode island, Kingston, Rl 02881)

Limited in situ measurements from high-frequency underwater acoustic echo sounders have suggested that there may be circumstances in which acoustic scattering from ocean temperaturę microstructure is sufficiently intense to be observablc over volume reverberation due to biologics. A ncw laboratory program, ocean acoustics turbulence study

J. Acoust. Soc. Am., Vol. 89, No. 4, Pt. 2, April 1991 (OATS), has been undertaken to quantify the naturę of such scattering and to compare laboratory results with a recently developed model of microstructure scattering. A buoyant plume characlerized by three dif-ferent types of fluid regions as a function of height, namely laminar, unstable, and fully developed turbulent, is used as the scattenng field. Experiments are to be performed in the frequency rangę from 100 kHz to 1 MHz for scattering angles spanning from near forward to near backscatter. Results to datę will be presented. Preliminary results have indicated observable acoustic scattering in all three fluid regions at 1 MHz, with the turbulent regimc yielding scattering strengths at a scattering angle of 90 deg of order — 80 dB in qualitative agreement with model predictions.

lfcOO

6UWS. Low-frequency backscattering from a submerged bubble cloud. Ronald A. Roy, Michael Nicholas, and Lawrence A. Crum (Natl. Ctr. for Physical Acoust., Univ. of Mississippi, University, MS 38677)

The results of a recent serics of experiments designed to demonstrate resonance backscattering from a bubble cloud are presented. in these experirnents, an ^l-m-diam bubble cloud was generated ~20 m be-neath the surface of a deep-water lakę and insonified using a pulsed parametric-array projector. Through measurements of frequcncy-dependent backscattering, target strengths were determined for frequen-cies ranging from 500 Hz to 4 kHz. (The individual bubble resonance frequcncies ranged from ~ I.S to ~5 kHz.) Results indieate an inereas-ing target strength with decreasing frequency, which suggests the pres-cnce of a resonance response in the subkilohertz rangę. Experimental results will be discusscd in light of theories describing the collcctive oscillations of bubble clouds and plumes. [Work supported by ONR, ONT, and AEAS.]

10:15

6UW6. Volume scattering measurements with a 12-kHz multibeam echo sounder. C. de Moustier (Marinę Physical Lab., Scripps Inst. of Oceanography, La Jolla, CA 92093-0205)

121st Meeting: Acoustical Society of Am en ca