On the spatial properties of ambient noise in the Tonga Trench, including effects of bathymetric shadowing

TitleOn the spatial properties of ambient noise in the Tonga Trench, including effects of bathymetric shadowing
Publication TypeJournal Article
Year of Publication2014
AuthorsBarclay DR, Buckingham MJ
JournalJournal of the Acoustical Society of America
Volume136
Pagination2497-2511
Date Published2014/11
Type of ArticleArticle
ISBN Number0001-4966
Accession NumberWOS:000344989000021
KeywordsCoherence; cross-correlation; deep-ocean; depth-dependence; directionality; fields; pacific; philippine sea; velocimeter; wind-driven
Abstract

In September 2012, the free-falling, deep-diving instrument platform Deep Sound III descended to the bottom of the Tonga Trench, where it resided at a depth of 8515 m for almost 3 h, recording ambient noise data on four hydrophones arranged in a vertical L-shaped configuration. The time series from each of the hydrophones yielded the power spectrum of the noise over the frequency band 3 Hz to 30 kHz. The spatial coherence functions, along with the corresponding cross-correlation functions, were recovered from all available hydrophone pairs in the vertical and the horizontal. The vertical coherence and cross-correlation data closely follow the predictions of a simple theory of sea-surface noise in a semi-infinite ocean, suggesting that the seabed in the Tonga Trench is a very poor acoustic reflector, which is consistent with the fact that the sediment at the bottom of the trench consists of very-fine-grained material having an acoustic impedance similar to that of sea-water. The horizontal coherence and cross-correlation data are a little more complicated, showing evidence of (a) bathymetric shadowing of the noise by the walls of the trench and (b) highly directional acoustic arrivals from the research vessel supporting the experiment. (C) 2014 Acoustical Society of America.

DOI10.1121/1.4896742
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