Acoustic measurements of the sound-speed profile in the bubbly wake formed by a small motor boat.

In situ measurements of the bubble field within wakes generated by a small motorboat show that the bubble field, shortly after the initial turbulent generation period, consists mainly of bubbles with radii between 20 and 200 microm. The subsequent dispersion of the wake field can be described using a model that includes bubble buoyancy and dissolution only, and the air volume fraction within the wakes decay exponentially with an e-folding time of between 40 and 60 s. Simultaneous measurements of sound propagating through the bubbly wake exhibit spectral banding due to waveguide propagation. Inversions using the inverse-square theory developed by Buckingham [Philos. Trans. R. Soc. London, Ser. A 335, 513-555 (1991)] show that this acoustic inversion technique provide a viable means of estimating the low-frequency sound-speed profile in an upward refractive bubble layer when dispersion can be neglected.

[1]  David M. Farmer,et al.  Waveguide propagation of ambient sound in the ocean-surface bubble layer , 1989 .

[2]  M. Buckingham.  On acoustic transmission in ocean-surface waveguides , 1991, Philosophical Transactions of the Royal Society of London. Series A: Physical and Engineering Sciences.

[3]  L. E. Horsley.  Modification and deployment techniques for hand-deployed Arctic long-life sonobuoys , 1989 .

[4]  D. Farmer,et al.  Acoustical measurements of microbubbles within ship wakes , 1994 .

[5]  S. Thorpe,et al.  On the clouds of bubbles formed by breaking wind-waves in deep water, and their role in air-sea gas transfer , 1982, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[6]  E. Terrill,et al.  A Broadband Acoustic Technique for Measuring Bubble Size Distributions: Laboratory and Shallow Water Measurements , 2000 .

[7]  R. Wildt.  Acoustic properties of wakes , 1968 .

[8]  Ocean Acoustic Propagation and Ambient Noise in a Surface Duct , 1993 .

[9]  R. Keeling.  On the role of large bubbles in air-sea gas exchange and supersaturation in the ocean , 1993 .

[10]  C. L. Trump,et al.  Preliminary Side-Scan ADCP Measurements across a Ship's Wake , 1996 .

[11]  D. M. Farmer,et al.  A comparison of four methods for bubble size and void fraction measurements , 1998 .

[12]  Herman Medwin,et al.  Acoustic miniprobing for ocean microstructure and bubbles , 1975 .

[13]  A. B. Wood.  A Text Book Of Sound , 1941 .

[14]  M. D. Stokes,et al.  Air Entrainment Processes and Bubble Size Distributions in the Surf Zone , 1999 .

[15]  W. Melville,et al.  SOUND-SPEED MEASUREMENTS NEAR THE OCEAN SURFACE , 1994 .

[16]  Herman Medwin,et al.  Acoustic fluctuations due to microbubbles in the near‐surface ocean , 1974 .

[17]  Eric Lamarre,et al.  Instrumentation for the measurement of void-fraction in breaking waves: laboratory and field results , 1992 .

[18]  David M. Farmer,et al.  A Free-Flooding Acoustical Resonator for Measurement of Bubble Size Distributions , 1998 .

[19]  Kerry W. Commander,et al.  Finite-element solution of the inverse problem in bubble swarm acoustics , 1991 .

[20]  W. Melville,et al.  Sound-speed measurements in the surface-wave layer , 1997 .

[21]  P. Wille,et al.  Measurements on the origin of the wind-dependent ambient noise variability in shallow water , 1984 .