Chotiros Nicholas P.

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Nicholas P.

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  • Article
    Estimate of the bottom compressional wave speed profile in the northeastern South China Sea using "Sources of Opportunity"
    (IEEE, 2004-10) Lin, Ying-Tsong ; Lynch, James F. ; Chotiros, Nicholas P. ; Chen, Chi-Fang ; Newhall, Arthur E. ; Turgut, Altan ; Schock, Steven G. ; Chiu, Ching-Sang ; Bartek, Louis R. ; Liu, Char-Shine
    The inversion of a broad-band "source of opportunity" signal for bottom geoacoustic parameters in the northeastern South China Sea (SCS) is presented, which supplements the towed source and chirp sonar bottom inversions that were performed as part of the Asian Seas International Acoustics Experiment (ASIAEX). This source of opportunity was most likely a "dynamite fishing" signal, which has sufficient low-frequency content (5-500 Hz) to make it complimentary to the somewhat higher frequency J-15-3 towed source (50-260 Hz) signals and the much higher frequency (1-10 kHz) chirp signals. This low frequency content will penetrate deeper into the bottom, thus extending the other inverse results. Localization of the source is discussed, using both a horizontal array for azimuthal steering and the "water wave" part of the pulse arrival for distance estimation. A linear broad-band inverse is performed, and three new variants of the broad-band inverse, based on: 1) the Airy phase; 2) the cutoff frequency; and 3) a range-dependent medium are presented. A multilayer model of the bottom compressional wave speed is obtained, and error estimates for this model are shown, both for the range-independent approximation to the waveguide and for the range-dependent waveguide. Directions for future research are discussed.
  • Article
    Inversion of surficial sediment thickness from under-ice acoustic transmission measurement
    (Acoustical Society of America, 2021-01-15) Chotiros, Nicholas P. ; Hope, Gaute ; Storheim, Espen ; Hobaek, Halvor ; Freitag, Lee E. ; Sagen, Hanne
    The under-ice acoustic transmission experiment of 2013, conducted under ice cover in the Fram Strait, was analyzed for bottom interactions for the purpose of developing a model of the seabed. Using the acoustic signals, as well as data from other sources, including cores, gravimetric, refraction, and seismic surveys, it was deduced that the seabed may be modeled as a thin surficial layer overlaid on a deeper sediment. The modeling was based on the Biot–Stoll model for acoustic propagation in porous sediments, aided by more recent developments that improve parameter estimation and depth dependence due to consolidation. At every stage, elastic and fluid approximations were explored to simplify the model and improve computational efficiency. It was found the surficial layer could be approximated as a fluid, but the deeper sediment required an elastic model. The full Biot–Stoll model, while instrumental in guiding the model construction, was not needed for the final computation. The model could be made to agree with the measurements by adjusting the surficial layer thickness.