Chiu Linus Y. S.

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Chiu
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Linus Y. S.
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  • Article
    Enhanced acoustic mode coupling resulting from an internal solitary wave approaching the shelfbreak in the South China Sea
    (Acoustical Society of America, 2013-03) Chiu, Linus Y. S. ; Reeder, D. Benjamin ; Chang, Yuan-Ying ; Chen, Chi-Fang ; Chiu, Ching-Sang ; Lynch, James F.
    Internal waves and bathymetric variation create time- and space-dependent alterations in the ocean acoustic waveguide, and cause subsequent coupling of acoustic energy between propagating normal modes. In this paper, the criterion for adiabatic invariance is extended to the case of an internal solitary wave (ISW) encountering a sloping bathymetry (i.e., continental shelfbreak). Predictions based on the extended criterion for adiabatic invariance are compared to experimental observations from the Asian Seas International Acoustics Experiment. Using a mode 1 starter field, results demonstrate time-dependent coupling of mode 1 energy to higher adjacent modes, followed by abrupt coupling of mode 5–7 energy to nonadjacent modes 8–20, produces enhanced mode coupling and higher received levels downrange of the oceanographic and bathymetric features. Numerical simulations demonstrate that increasing ISW amplitude and seafloor slope enhance the coupling of energy to adjacent and nonadjacent modes. This enhanced coupling is the direct result of the simultaneous influence of the ISW and its proximity to the shelfbreak, and, compared to the individual effect of the ISW or shelfbreak, has the capacity to scatter 2–4 times the amount of acoustic energy from below the thermocline into the upper water column beyond the shelfbreak in realistic environments.
  • Technical Report
    Acoustics and oceanographic observations collected during the QPE Experiment by Research Vessels OR1, OR2 and OR3 in the East China Sea in the Summer of 2009
    (Woods Hole Oceanographic Institution, 2010-08) Newhall, Arthur E. ; Lynch, James F. ; Gawarkiewicz, Glen G. ; Duda, Timothy F. ; McPhee, Neil M. ; Bahr, Frank B. ; Marquette, Craig D. ; Lin, Ying-Tsong ; Jan, Sen ; Wang, Joe ; Chen, Chi-Fang ; Chiu, Linus Y. S. ; Yang, Yiing-Jang ; Wei, Ruey-Chang ; Emerson, Chris ; Morton, David ; Abbot, Ted ; Abbot, Philip A. ; Calder, Brian ; Mayer, Larry A. ; Lermusiaux, Pierre F. J.
    This document describes data, sensors, and other useful information pertaining to the ONR sponsored QPE field program to quantify, predict and exploit uncertainty in observations and prediction of sound propagation. This experiment was a joint operation between Taiwanese and U.S. researchers to measure and assess uncertainty of predictions of acoustic transmission loss and ambient noise, and to observe the physical oceanography and geology that are necessary to improve their predictability. This work was performed over the continental shelf and slope northeast of Taiwan at two sites: one that was a relatively flat, homogeneous shelf region and a more complex geological site just shoreward of the shelfbreak that was influenced by the proximity of the Kuroshio Current. Environmental moorings and ADCP moorings were deployed and a shipboard SeaSoar vehicle was used to measure environmental spatial structure. In addition, multiple bottom moored receivers and a horizontal hydrophone array were deployed to sample transmission loss from a mobile source and ambient noise. The acoustic sensors, environmental sensors, shipboard resources, and experiment design, and their data, are presented and described in this technical report.
  • Article
    Surficial sediment sound speed estimation from wide-angle multipath arrivals
    (Acoustical Society of America, 2022-11) Chiu, Linus Y. S. ; Lin, Ying-Tsong
    Multipath acoustic arrivals on fixed receivers from a moving source in an underwater waveguide include wide-angle bottom reflections that are affected by sediment properties. Hence, one can use them as input data for seabed geoacoustic parameter estimation. In this study, the effects of seabed properties on such measurements are theoretically analyzed. The result shows that one can utilize time delays and source distances at the critical angle points of multipath arrivals to determine the sediment sound speed. The effect of sediment attenuation is also discussed, and the proposed method is demonstrated with experimental data.
  • Article
    Effects of nonlinear internal gravity waves on normal-incident reflection measurements of seafloor sediments
    (Acoustical Society of America, 2023-01-18) Chen, Tzu-Ting ; Chiu, Linus Y.-S. ; Lin, Ying-Tsong
    Sonar data acquired by sub-bottom profilers and echosounder systems are widely used to estimate geoacoustic properties of marine sediments. However, the uncertainty of the seabed property estimates caused by water-column variability may limit the application. In this paper, the acoustic focusing and defocusing effects of nonlinear internal gravity waves on normal-incident acoustic reflection measurements are studied. The experiment data were collected in the South China Sea from two transceiver moorings located at two different sites, one of which contained strong nonlinear internal waves (NIWs), while another site did not. The observed reflection intensity variation at the internal wave site varied up to 10 dB. On the other hand, the bottom reflections at the other site without internal waves were stable, and a seafloor sediment sample collected there was analyzed to validate the sediment type inferred from bottom loss. Numerical simulations using ray-tracing and parabolic equation models confirmed the cause of this intensity fluctuation by the acoustic focusing and defocusing of NIWs. This study eventually showed that NIWs may induce a significant bias for geoacoustic property estimates from seabed reflection coefficients.