Observations of sound-speed fluctuations in the western Philippine Sea in the spring of 2009

J Acoust Soc Am. 2013 Oct;134(4):3185-200. doi: 10.1121/1.4818784.

Abstract

As an aid to understanding long-range acoustic propagation in the Philippine Sea, statistical and phenomenological descriptions of sound-speed variations were developed. Two moorings of oceanographic sensors located in the western Philippine Sea in the spring of 2009 were used to track constant potential-density surfaces (isopycnals) and constant potential-temperature surfaces (isotherms) in the depth range 120-2000 m. The vertical displacements of these surfaces are used to estimate sound-speed fluctuations from internal waves, while temperature/salinity variability along isopycnals are used to estimate sound-speed fluctuations from intrusive structure often termed spice. Frequency spectra and vertical covariance functions are used to describe the space-time scales of the displacements and spiciness. Internal-wave contributions from diurnal and semi-diurnal internal tides and the diffuse internal-wave field [related to the Garrett-Munk (GM) spectrum] are found to dominate the sound-speed variability. Spice fluctuations are weak in comparison. The internal wave and spice frequency spectra have similar form in the upper ocean but are markedly different below 170-m depth. Diffuse internal-wave mode spectra show a form similar to the GM model, while internal-tide mode spectra scale as mode number to the minus two power. Spice decorrelates rapidly with depth, with a typical correlation scale of tens of meters.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Acoustics* / instrumentation
  • Models, Statistical
  • Motion
  • Oceanography / instrumentation
  • Oceanography / methods*
  • Oceans and Seas
  • Philippines
  • Seasons*
  • Seawater*
  • Signal Processing, Computer-Assisted
  • Signal-To-Noise Ratio
  • Sound Spectrography
  • Sound*
  • Surface Properties
  • Temperature
  • Time Factors
  • Transducers