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  • 1
    Publication Date: 2018-08-30
    Description: Upstream mean semidiurnal internal tidal energy flux has been found in the Gulf Stream in hydrodynamical model simulations of the Atlantic Ocean. A major source of the energy in the simulations is the south edge of Georges Bank, where strong and resonant Gulf of Maine tidal currents are found. An explanation of the flux pattern within the Gulf Stream is that internal wave modal rays can be strongly redirected by baroclinic currents and even trapped (ducted) by current jets that feature strong velocities above the thermocline that are directed counter to the modal wavenumber vector (i.e., when the waves travel upstream). This ducting behavior is analyzed and explained here with ray-based wave propagation studies for internal wave modes with anisotropic wavenumbers, as occur in mesoscale background flow fields. Two primary analysis tools are introduced and then used to analyze the strong refraction and ducting: the generalized Jones equation governing modal properties and ray equations that are suitable for studying waves with anisotropic wavenumbers.
    Print ISSN: 0022-3670
    Electronic ISSN: 1520-0485
    Topics: Geosciences , Physics
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  • 2
    Publication Date: 1996-12-15
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 3
  • 4
    Publication Date: 2022-05-25
    Description: The NOAA National Underseas Research Program at Rutgers University is establishing a Long-term Ecosystem Observatory off New Jersey in 15 meters of water. As part of a bottom boundary layer study at this site, WHOI deployed a bottom instrument frame during the winter of 1993-94. The bottom instrument carried a current meter, a vertical array of optical back scattering sensors, temperature, pressure and conductivity sensors and an Acoustical Backscattering Sensor. The deployment was partially successful as the acoustic system failed. The other instrumentation worked well for 3 weeks returning data on winter conditions at the site. The extreme winter waves ended the experiment by tipping the instrument over on its side. The optical instrumentation was calibrated with sediment from the site, and the results from the experiment presented.
    Description: Funding was provided by the National Oceanic and Atmospheric Administration through Contract No. 4-25020 to Rutgers/SUNY National Underseas Research Program.
    Keywords: Sediment transport ; LEO-15 ; Acoustic backscatter
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
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  • 5
    Publication Date: 2022-05-25
    Description: Author Posting. © IEEE, 2004. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 29 (2004): 1264-1279, doi:10.1109/JOE.2004.836997.
    Description: We present analyses of fluctuations seen in acoustic signals transmitted by two 400-Hz sources moored as part of the ASIAEX 2001 South China Sea (SCS) experiment. One source was near the bottom in 350-m deep water 31.3 km offshore from the receiving array, and the other was near the bottom in 135-m deep water 20.6 km alongshore from the array. Time series of signal intensity measured at individual phones of a 16-element vertical line array are analyzed, as well as time series of intensity averaged over the array. Signals were recorded from 2 May to 17 May 2001. Fluctuations were observed at periods ranging from subtidal (days) to the shortest periods resolved with our signaling (10 s). Short-period fluctuations of depth- and time-averaged intensity have scintillation indexes (computed within 3-h long windows) which peak at values near 0.5 during an interval of numerous high-amplitude internal gravity waves, and which are lower during intervals with fewer internal waves. The decorrelation times of the averaged intensity (energy level) are also closely related to internal wave properties. Scintillation indexes computed for unaveraged pulses arriving at individual phones often exceed unity.
    Description: This work was supported by the U.S. Office of Naval Research.
    Keywords: Acoustic intensity ; Fluctuation ; Underwater acoustic propagation
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 6
    Publication Date: 2022-05-25
    Description: Author Posting. © IEEE, 2004. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 29 (2004): 1308-1315, doi:10.1109/JOE.2004.836999.
    Description: This correspondence presents a preliminary examination of the low frequency ambient noise field measured in the South China Sea component of the Asian Seas International Acoustics Experiment (ASIAEX), concentrating on the frequencies of 50, 100, 200, 400, 800, and 1200 Hz. A two-week-long time series of the noise at these frequencies is examined for structure in both the time and frequency domains. Three features of particular interest in these series are: 1) the noise due to a typhoon, which passed near the experimental site, 2) the weak tidal frequency variability of the noise field, which is probably due to internal tide induced variability in the propagation conditions, and 3) the vertical angle dependence of the noise, particularly as regards the shallow water "noise notch" phenomenon. The acoustic frequency dependence and the vertical dependence of the noise field are also examined over the course of the time series. A simple look at the noise variability statistics is presented. Finally, directions for further analysis are discussed.
    Description: This work was supported by the U.S. Office of Naval Research under Grants N0001498-1-0413, N00014-00-0931, and N00014-01-0772 and by the NSC of Taiwan under Grant NSC92-2611-E110-004-CCS.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 7
    Publication Date: 2022-05-25
    Description: Author Posting. © Oceanography Society, 2007. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 20, 4 (2007): 156-167.
    Description: Since the end of the Cold War, the US Navy has had an increasing interest in continental shelves and slopes as operational areas. To work in such areas requires a good understanding of ocean acoustics, coastal physical oceanography, and, in the modern era, autonomous underwater vehicle (AUV) operations.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 8
    Publication Date: 2022-05-25
    Description: Author Posting. © IEEE, 2010. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 35 (2010): 12-27, doi:10.1109/JOE.2009.2038512.
    Description: Nonlinear internal waves in shallow water have been shown to be effective ducts of acoustic energy, through theory, numerical modeling, and experiment. To date, most work on such ducting has concentrated on rectilinear internal wave ducts or those with very slight curvature. In this paper, we examine the acoustic effects of significant curvature of these internal waves. (By significant curvature, we mean lateral deviation of the internal wave duct by more than half the spacing between internal waves over an acoustic path, giving a transition from ducting to antiducting.) We develop basic analytical models of these effects, employ fully 3-D numerical models of sound propagation and scattering, and examine simultaneous acoustical and oceanographic data from the 2006 Shallow Water Experiment (SW06). It will be seen that the effects of curvature should be evident in the mode amplitudes and arrival angles, and that observations are consistent with curvature, though with some possible ambiguity with other scattering mechanisms.
    Description: This work was supported by E. Livingston and T. Pawluskiewicz of the U.S. Office of Naval Research (ONR) under Grant N00014–04-1–0146 and the ONR postdoctoral fellowship award Grant N00014-08-1-0204.
    Keywords: Horizontal acoustic ducting ; Horizontal acoustic refraction ; Horizontal acoustic shadowing ; Shallow-water acoustics ; Curved nonlinear internal waves
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 9
    Publication Date: 2022-05-25
    Description: Author Posting. © Acoustical Society of America, 2012. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 131 (2012): 1762-1781, doi:10.1121/1.3672644.
    Description: To understand the issues associated with the presence (or lack) of azimuthal isotropy and horizontal (along isobath) invariance of low-frequency (center frequencies of 600 Hz and 900 Hz) acoustic propagation in a shelfbreak environment, a series of experiments were conducted under the Autonomous Wide-Aperture Cluster for Surveillance component of the Shallow Water 2006 experiment. Transmission loss data reported here were from two mobile acoustic sources executing (nearly) circular tracks transmitting to sonobuoy receivers in the circle centers, and from one 12.5 km alongshelf acoustic track. The circle radii were 7.5 km. Data are from September 8, 2006. Details of the acoustic and environmental measurements are presented. Simple analytic and computer models are used to assess the variability expected due to the ocean and seabed conditions encountered. A comparison of model results and data is made, which shows preliminary consistency between the data and the models, but also points towards further work that should be undertaken specifically in enlarging the range and frequency parameter space, and in looking at integrated transmission loss.
    Description: Office of Naval Research Code 32.
    Keywords: Acoustic radiators ; Acoustic receivers ; Acoustic variables measurement ; Acoustic wave propagation ; Acoustic wave transmission ; Invariance ; Underwater sound
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 10
    Publication Date: 2022-05-25
    Description: A joint acoustics and physical oceanography experiment was conducted in the winter of 1997 on the shell break and continental slope south of New England in the Middle Atlantic Bight (figure 1). This experiment, Primer4, provided a seasonal contrast to the previous summer Primer3 experiment and had the same goals and tasks: to study the thermohaline variability and structure of the shelfbreak front and its effects on acoustic propagation. To accomplish the linked oceanographic and acoustic objectives of this experiment, a combination of measurements (fig 2) were made. Seasoar hydrography, shipboard ADCP measurements, Satellite IR sea surface temperature field observations, and AXT drops were employed to study the larger scale oceanographic fields. To study the finer scale, which includes internal waves, a number of rapid-sampling thermistor strings and current meters, including a moored, upward looking ADCP, were deployed. The acoustics components consisted of three 400 Hz tomography transceivers, a 224 Hz source and two hydrophone arrays. To study the geoacoustic parameters in the bottom a number of SUS charges were also deployed. The field setup was approximately the same for both the summer 1996 and winter 1997 experiments; however the weather conditions and the thermal structure of the mixed layer were radically different. This report is dedicated to the data from the Winter 1997 Primer4 experiment.
    Description: Funding was provided by the Offce of Naval Research under Contract No. NOOOl4-98-10413.
    Keywords: Primer experiment ; Shallow water acoustics ; Shelfbreak front ; Endeavor (Ship: 1976-) Cruise
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
    Format: 6103327 bytes
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