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Refraction of Sound by Islands and Seamounts

Munk, W. H. and Zachariasen, F. (1991) Refraction of Sound by Islands and Seamounts. Journal of Atmospheric and Oceanic Technology, 8 (4). pp. 554-574. ISSN 0739-0572. doi:10.1175/1520-0426(1991)008<0554:ROSBIA>2.0.CO;2.

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We consider the propagation into shallow water of low-frequency and low-order acoustic modes trapped in the sound channel. The phase velocity slightly decreases and then increases with decreasing depth. This leads to an unusual pattern of wave refraction. Waves are “attracted” by islands and seamounts (rays turn toward shore) in “almost deep” water, and then are strongly “repelled” in shallow water. We examine the relative intensity of scattered arrivals in very long-range ocean transmissions. Forward scatter by islands and seamounts can give significant (order −10 dB) scattered arrivals, as can large-angle scatter (including backscatter) by large islands and by islands near the source or receiver. However, transmission of acoustic energy into the sea floor leads to loss of the scattered energy in the sound channel. Total reflection (no loss) is favored by glancing incidence on steep slopes of islands and seamounts with large compressional seismic velocities. We suggest a complementary relation between the intensities from an underwater explosion as recorded on axial hydrophones versus nearby land seismometers, with conditions favorable to reflection favoring hydrophones and vice versa. A preliminary attempt is made to compare measured and computed scattered intensities in the sound channel for operation WIGWAM (a deep-water nuclear explosion in 1955), operation CHASE, and the Perth to Bermuda transmission of 1960. Computed intensities are too low.

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Additional Information:© 1991 American Meteorological Society Manuscript received August 9, 1990, in final form January 3, 1991 A preliminary draft of this paper was prepared during the JASON Summer Study 1989 as part of an examination of acousti c detection of global ocean warming; F.Z. acknowledges support from the Department of Energy. W.M. holds the Secretary of the Navy Research Chair in Oceanography.
Issue or Number:4
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:5987
Deposited By: Archive Administrator
Deposited On:10 Nov 2006
Last Modified:08 Nov 2021 20:30

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