Thesis (Ph. D.)--University of Wisconsin--Madison, 1973. / Vita. Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2006. / Includes bibliographical references (p. 155-169).

Originally issued as the author's thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2006. / "February 2006". "Doctoral dissertation." "Department of origin: Applied Ocean Physics and Engineering." "Joint Program in Oceanography/Applied Ocean Science and Engineering"--Cover. Bibliography: p. 197-206.

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The purposes of this research have been to determine a) the basic physical causes of acoustic scattering from zooplanktonic organisms and b) necessary criteria for future acoustic studies involving these animals. In situ measurements at 102 kHz have been made of the scattering of sound from a volumetric distribution of a zooplanktonic organism, the euphausiid. Quantitative information was recorded on analog magnetic tape and subsequently converted to digital form for analysis. Based on simultaneous measurements of side and back scattering from euphausiids and on a mathematical model, four-fifths of the scattered sound is considered to be caused by the compressibility contrast between the animals and the sea water. The remaining one-fifth is attributed to density contrast. Acoustic energy distribution curves are characteristic of the number and size of the animals contained in the small volume of the ocean that was studied. Acoustic counting of the animals gave results that compared favourably with simultaneous controlled net sampling. The back scattering cross-section of a typical euphausiid at 102 kHz has been found to be 1.4 x 10⁻⁴ cm² . Based on this value it is possible to predict the optimum frequency and intensity of incident sound for future acoustic studies involving these animals. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Quantitative volume-scattering measurements were compared to the distribution of euphausiids in Saanich Inlet, British Columbia. Scattering was recorded at 42, 107, and 200 kHz from the depths of high euphausiid concentrations, and volume-scattering coefficients were determined. No scattering from euphausiids was recorded by a 11 kHz echo-sounder. Daily variations in the volume-scattering coefficients, m(Δz), generally compared well with variations in the concentration of euphausiids. The daily behaviour of the high-frequency scattering layer., and therefore m(Δz) and the concentration of euphausiids, was influenced by moonlight and weather conditions as well as the presence or absence of an oxycline in the inlet. In the absence of an oxycline conditions would have been closer to conditions in the open ocean. Under these circumstances euphausiid concentrations and m(Δz) were low in the mornings and gradually increased throughout the day; the high-frequency scattering layer consolidated. During the evening migration, the layer became more diffuse, and the number of euphausiids per cubic metre decreased. The scattering cross-section, σ (cm²), of a euphausiid was found to increase with the average dry weight and length, and with increased frequency. For each cruise σ was approximately one order of magnitude apart at the three frequencies. The values of σ (in cm²) ranged from 4.81 x 10⁻⁵ to 5.21 x 10⁻³(200 kHz), 5.49 x 10⁻⁶ to 3.99 x 10⁻⁴ (107 kHz), and 2.30 x 10⁻⁷ to 3.67 x 10⁻⁵ (42 kHz). / Science, Faculty of / Zoology, Department of / Graduate

This Research Report presents some of the equations of underwater acoustics that relate to the signal excess noise received by a transducer. The basic structural equation is developed, as are defining equations for each term in that equation. An analysis is performed utilizing typical values to ascertain if the elements of the structural equation can be simplified. Results delineate that several terms of that equation can be neglected while maintaining a relative high degree of accuracy.

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This thesis is concerned with long-range sound propagation in deep water.  The main area of interest is the stability of acoustic ray paths in wave guides in which there is a transition from single to double duct sound speed profiles, or vice-versa.  Sound propagation is modelled within a ray theoretical framework, which facilitates a dynamical systems approach of understanding long-range propagation phenomena, and the use of its tools of analysis. Alternative reduction techniques to the Poincaré sections are presented, by which the stability of acoustic rays can be graphically determined.  Beyond periodic driving, these techniques prove to be useful in case of the simplest quasiperiodic driving of the ray equations.  One of the techniques facilitates a special representation of ray trajectories for periodic driving. Namely, the space of sectioned trajectories is partitioned into nonintersecting regular and chaotic regions as with the Poincaré sections, when quasiperiodic and chaotic trajectories are represented by curve segments and area filling points, respectively.  In case of the simplest quasiperiodic driving – speaking about the same technique – regular trajectories are represented by curves similar to Lissajous curves, which are opened or closed depending on whether the two driving frequencies involved make relative primes or not. It is confirmed for a perturbed canonical profile that the background sound speed structure controls ray stability. It is also demonstrated for a particular double duct profile, when the singularity of the nonlinearity parameter for the homoclinic trajectory associated with this profile refers to the strong instability of corresponding perturbed trajectories.