title: Depth dependence of wind-driven, broadband ambient noise in the Philippine Sea.
abstract: 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 θ, where θ ≤ 90° 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.
authors.affiliation: Marine Physical Laboratory, Scripps Institution of Oceanography University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0238, USA.
authors.forename: David R
authors.initials: DR
authors.lastname: Barclay
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Buckingham
mesh_terms: D000162:Acoustics / Q000295:instrumentation; D000465:Algorithms; D008962:Models, Theoretical; D009038:Motion; D009622:Noise; D009792:Oceans and Seas; D012815:Signal Processing, Computer-Assisted; D013018:Sound Spectrography; D013997:Time Factors; D014867:Water; D014919:Wind
chemical_list: D014867:Water