Browsing by Author "Courtney, Jennifer Susan"

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    Antipodal receptions in global acoustics
    (1997) Courtney, Jennifer Susan; Brundrit, Geoff
    Global Acoustic Propagation is a recently developed scientific discipline within the study of long range underwater acoustic propagation. Acoustic propagation over extremely long ranges involves a combination of effects from earth curvature and the global distribution of oceanographic and geophysical features. Antipodal receptions, that is to ranges of the order of 20Mm (1 Megameter = 1 000 km), require underwater acoustic propagation to very long ranges and thus effects due to the form of the earth and the range dependence of the sound speed field within the ocean can not be ignored. The purpose of this thesis is to investigate the nature of antipodal receptions with reference to the form of the earth and horizontal sound speed variations within the ocean and thereby contribute to the new and specialized field of study, Global Acoustic Propagation. Close to an acoustic source acoustic energy diverges so that local signal strengths decrease with distance from the source. However, as the antipodal region is approached acoustic energy that has not been blocked by bathymetric features will refocus, counteracting the distance loss rule. Thus at antipodal sites there is a good prospect of receiving a focused signal. Even so, the ellipsoidal form of the earth and the horizontal variability within the sound speed field of the ocean means that the re-focusing will result in a region of enhanced signal rather than an exact antipodal point. The precise detail of the advantage of placing receivers in the antipodal region will depend upon the paths taken by the acoustic energy and the characteristics of the acoustic medium encountered along each path. The proposal for this thesis is to develop an algorithm to determine the nature of the antipodal region under certain physical assumptions. The physical assumptions are referred to as the geometric assumption, which refers to the form of the earth, and the refractive assumption, which refers to the horizontal variability of sound speed within the world oceans.
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    Modeling studies of acoustic propagation through the Agulhas Current region
    (1994) Courtney, Jennifer Susan; Brundrit, Geoff B
    The motivation for this thesis arises from the apparent global warming problem. It is common knowledge that the ocean is an important heat sink and that to predict global warming trends it is important to measure changes in the ocean temperature. Measurements of ocean temperature are subject to large local variability associated with mesoscale features. In order to measure global warming trends a method is required to determine large scale averages, over large oceanic ranges, in order to remove the inherent variability associated with mesoscale features, such as currents and mesoscale eddies. This requirement can be met by acoustic thermometry.