Depth dependence of wind-driven, broadband ambient noise in the Philippine Sea

TitleDepth dependence of wind-driven, broadband ambient noise in the Philippine Sea
Publication TypeJournal Article
Year of Publication2013
AuthorsBarclay DR, Buckingham MJ
JournalJournal of the Acoustical Society of America
Date Published2013/01
Type of ArticleArticle
ISBN Number0001-4966
Accession NumberWOS:000313034700019
Keywordscross-correlation; deep-ocean; fields; pacific; site; spatial-correlation; spectra; vertical directionality

In 2009, as part of PhilSea09, the instrument platform known as Deep Sound was deployed in the Philippine Sea, descending under gravity to a depth of 6000 m, where it released a drop weight, allowing buoyancy to return it to the surface. On the descent and ascent, at a speed of 0.6 m/s, Deep Sound continuously recorded broadband ambient noise on two vertically aligned hydrophones separated by 0.5 m. For frequencies between 1 and 10 kHz, essentially all the noise was found to be downward traveling, exhibiting a depth-independent directional density function having the simple form cos theta, where theta <= 90 degrees is the polar angle measured from the zenith. The spatial coherence and cross-spectral density of the noise show no change in character in the vicinity of the critical depth, consistent with a local, wind-driven surface-source distribution. The coherence function accurately matches that predicted by a simple model of deep-water, wind-generated noise, provided that the theoretical coherence is evaluated using the local sound speed. A straightforward inversion procedure is introduced for recovering the sound speed profile from the cross-correlation function of the noise, returning sound speeds with a root-mean-square error relative to an independently measured profile of 8.2 m/s. (C) 2013 Acoustical Society of America. 

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