Bottom interaction of low-frequency acoustic signals at small grazing angles in the deep ocean
Citable URI
https://hdl.handle.net/1912/10269DOI
10.1575/1912/10269Keyword
Marine sediments; Acoustical engineeringAbstract
The results of a deep-ocean bottom interaction experiment are presented in which the effects of both bottom
refraction and subbottom reflection were observed. Data were obtained in the Hatteras Abyssal Plain using a
deep towed 220-Hz pulsed cw source and two receivers anchored near the bottom. For ranges between 1 and
6 km, corresponding to bottom grazing angles less than 13°, the quadrature components of the received
signals were recorded digitally. The observed amplitude shows a strong spatial interference pattern which is
composed of the direct and bottom interacting arrivals. It is shown that for small source-receiver separations,
the bottom return is dominated by a strong subbollom reflection. With increasing separation, this arrival
evolves into a refracted arrival due to the presence of a positive sound-speed gradient in the sediment
overlying the subbottom. Because of the gradient, a caustic is formed, and corresponding high intensity
regions are observed in the data at the expected ranges. Values of sediment layer thickness, sound-speed
gradient, and sound-speed drop at the water-bollom interface are obtained from best fits to the data using ray
theory, normal mode theory, and the parabolic equation method. These values are consistent with those
obtained in nearby locations by other workers. The success of the parabolic equation method indicates that at
small grazing angles, the bottom interaction process may be modeled as a propagation process combined with
the effect of a perfect, soft subbollom reflector. A value of sediment attenuation, 0.0015 dB/mat 220Hz, is
also inferred from the data and is among the lowest values reported to date in the literature.
Description
Also published as: Journal of the Acoustical Society of America 69 (1981): 84-94
Suggested Citation
Frisk, G. V., Doutt, J. A., & Hays, E. E. (1981). Bottom interaction of low-frequency acoustic signals at small grazing angles in the deep ocean. Woods Hole Oceanographic Institution. https://doi.org/10.1575/1912/10269Related items
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