The contribution of normal modes in the bottom to the acoustic field in the ocean
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The effects of normal modes in the bottom on the acoustic field in the ocean are examined. The ocean bottom model consists of a slow isovelocity layer overlying an isovelocity half-space to simulate the characteristic sound velocity drop at the water-bottom interface. Attention is focused on the perfectly trapped modes which are excited in the layer by inhomogeneous waves emitted by a point source in the water column. The relative normal mode contribution to the total acoustic field in the water is calculated analytically for a near-bottom source/receiver geometry and evaluated for representative ocean bottom examples. It is shown that, for combined source/receiver heights less than a wavelength, the field is dominated by the leaky mode contribution at short ranges ( $ 2 km) and the trapped mode contribution at long ranges ( ~ 2 km). For fixed bottom parameters, the trapped mode contribution increases exponentially with decreasing combined source/receiver height. It is also shown that, for a fixed layer wavenumber-thickness product and fixed layer sound speed, the leaky mode fields at different frequencies are approximately range-scaled versions of the same field.
Also published as: Journal of the Acoustical Society of America 68 (1980): 602-612
Suggested CitationMacpherson, M. K., & Frisk, G. V. (1981). The contribution of normal modes in the bottom to the acoustic field in the ocean. Woods Hole Oceanographic Institution. https://doi.org/10.1575/1912/10241
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