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  • Biological effects of acoustic radiation  (1)
  • Ocean waves  (1)
  • 1
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    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Publication Date: 2022-05-25
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1987
    Description: This thesis develops a new technique for estimating quasi-homogeneous and quasi-stationary sea surface wave frequency-direction spectra using acoustic tomography. The analysis of acoustic (mode and ray) phase and travel time perturbations due to a rough sea surface is presented. Two canonical waveguides (ideal shallow water and linear squared index of refraction) are used as examples for the mode perturbation. The analysis is used to explain high mode coherence measured in the FRAM N experiment. The forward problem of computing the acoustic phase and travel time perturbation spectra given the surface wave spectrum is solved to first order. An application of the technique to ray phase data taken during the MIZEX '84 experiment is shown. The inverse problems for the homogeneous and quasi-homogel1eous frequency-direction spectrum are introduced. The theory is applied to synthetic data which simulate a fetch-dependent sea. The estimates made agree well with the "actual" (synthetic data) spectrum. The effect of noise in the travel time estimates is studied. The sensitivity of the technique. to the number of rays used in the inversion is investigated and the resolution and variance of the inverse method are addressed.
    Description: gratefully acknowledge the financial support of the Office of Naval Research, the General Electric Foundation, and the Ford Foundation.
    Keywords: Ocean waves
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
    Format: application/pdf
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  • 2
    Publication Date: 2022-05-25
    Description: Author Posting. © Acoustical Society of America, 2007. 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 121 (2007): 3011-3020, doi:10.1121/1.2713555.
    Description: The introduction of anthropogenic sound to coastal waters is a negative side effect of population growth. As noise from boats, marine construction, and coastal dredging increases, environmental and behavioral monitoring is needed to directly assess the effect these phenomena have on marine animals. Acoustic recordings, providing information on ambient noise levels and transient noise sources, were made in two manatee habitats: grassbeds and dredged habitats. Recordings were made over two 6-month periods from April to September in 2003 and 2004. Noise levels were calculated in one-third octave bands at nine center frequencies ranging from 250 Hz to 64 kHz. Manatee habitat usage, as a function of noise level, was examined during four time periods: morning, noon, afternoon, and night. Analysis of sightings data in a variety of grassbeds of equal species composition and density indicate that manatees select grassbeds with lower ambient noise for frequencies below 1 kHz. Additionally, grassbed usage was negatively correlated with concentrated boat presence in the morning hours; no correlation was observed during noon and afternoon hours. This suggests that morning boat presence and its associated noise may affect the use of foraging habitat on a daily time scale.
    Description: This research was supported by a P.E.O. Scholar Award and National Defense Science and Engineering Graduate Fellowship awarded to Jennifer Miksis.
    Keywords: Bioacoustics ; Biological effects of acoustic radiation ; Acoustic noise ; Boats
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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