Neilsen Tracianne B.

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Neilsen
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Tracianne B.
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  • Article
    Maximum entropy inference of seabed properties using waveguide invariant features from surface ships
    (Acoustical Society of America, 2022-04-28) Knobles, David P. ; Neilsen, Tracianne B. ; Wilson, Preston S. ; Hodgkiss, William S. ; Bonnel, Julien ; Lin, Ying-Tsong
    coustic data were recorded on two vertical line arrays (VLAs) deployed in the New England Mud Patch during the Seabed Characterization Experiment 2017 in about 75 m of water. The sound recorded during the passage of merchant ships permits identification of singular points for the waveguide invariant β for mode pairs (1,𝑛):𝛽1,𝑛,for 𝑛=2,3,4,5, in the 15–80 Hz band. Using prior geophysical information and an acoustic data sample from the merchant ship KALAMATA, a geoacoustic model 𝔐 of the seabed was developed. Then, using data samples from other merchant ships, a feature-ensemble maximum entropy method is employed to infer the statistical properties of geoacoustic parameter values for the sound speeds in a surface mud layer and a deep sand layer. Technical challenges include a sparsity of observed singular points, the unique identification of mode pairs for an observed singular point, and the deviation of the waveguide from horizontal stratification. A geoacoustic model 𝔐 is developed that reproduced the observed 𝛽≈−1 for f < 20 Hz and mode cutoff features at about 15 Hz. The statistical low-frequency inference of the singular point structure from multiple ships provides evidence of an angle of intromission at the water sediment interface with an average sound speed ratio of about 0.986 and an average sound speed for the deeper sand layer of about 1775 m/s.
  • Article
    Feature-based maximum entropy for geophysical properties of the seabeda)
    (Acoustical Society of America, 2024-06-03) Knobles, David P. ; Hodgkiss, William S. ; Chaytor, Jason D. ; Neilsen, Tracianne B. ; Lin, Ying-Tsong
    The coherent recombination of a direct and seabed reflected path is sensitive to the geophysical properties of the seabed. The concept of feature-based inversion is used in the analysis of acoustic data collected on a vertical line array (VLA) on the New England continental shelf break in about 200 m of water. The analysis approach for the measurements is based on a ray approach in which a direct and bottom reflected path is recombined, resulting in constructive and destructive interference of the acoustic amplitudes with frequency. The acoustic features have the form of prominent nulls of the measured received levels as a function of frequency as a broadband (500–4500 Hz) source passes the closest point of approach to the VLA. The viscous grain shearing (VGS) model is employed to parameterize a two-layer seabed model. The most likely seabed is a sand sediment with a porosity of about 0.42. There is a possibility of a thin (less than 0.5 m) surface layer having a slightly higher porosity between 0.45 and 0.50. Using the estimates for the VGS parameters inferred from the short-range frequency features, a normal mode model is used to predict the received acoustic levels over larger range scales.