Acoustic and microwave signatures of breaking waves

Melville, W. Kendall; Loewen, Mark; Felizardo, Francis C.; Jessup, Andrew T.; Buckingham, Michael J.

doi:10.1038/336054a0

Cited by 64 publications

(34 citation statements)

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“…Melville et al (1988) observed that the acoustic energy radiated and the microwave power backscattered by breaking waves in the laboratory correlated with the wave slope and the energy dissipation This was the first conclusive evidence that measurements of the sound and backscattered microwave power produced by breaking waves could be used to quantitatively study the dynamics of breaking waves.…”

mentioning

confidence: 94%

“…shows a set of data from our earlier experiments, which were reported in Melville et al (1988), showing the attenuation of the mean square acoustic pressure, p2 (x), where where p(x,t) is the acoustic pressure, and T is the duration of the sampling intervaL The attenuation rate is approximately constant for a given slope, S, and at a given x location the mean square pressure increases with increasing S. In the present study hydrophone measurements were taken over a range of 4m in the x direction for one third of the events, and over a range of 2 m for the remaining events. Extrapolating over twice the distance from the sampling location of the hydrophone to the wavemaker paddle or to the endwall showed that the sound had decayed to negligible levels before returning to the hydrophone location.…”

Section: 21mentioning

confidence: 99%

“…Melville, J. Fluid Mech., 224, 601-623, 1991. The research was motivated by the fact that preliminary measurements by Melville, Loewen, Felizardo, Jessup and Buckingham (1988) demonstrated that both the microwave power back scattered and the sound radiated by breaking waves correlated with the dynamics of breaking. Specifically, they found that the mean square acoustic pressure and the backscattered microwave correlated with the fractional energy dissipation.…”

Section: Chapter L; Microwaye Ilwl Acoustic Experimentsmentioning

confidence: 99%

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Laboratory measurements of the sound generated by breaking waves

Loewen¹

1991

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in partial fulfillment of the requirements for the Degree of Doctor of Philosophy in Oceanographic EngineeringBreaking waves dissipate energy, transfer momentum from the wind to surface currents and breaking enhances the transfer of gas and mass across the air-sea interface. Breaking waves are believed to be the dominant source of sea surface sound at frequencies greater than 500 Hz and the presence of breaking waves on the ocean surface has been shown to enhance the scattering of microwave radiation. Previous studies have shown that breaking waves can be detected by measuring the microwave backscatter and acoustic radiation from breaking waves. However, these techniques have not yet proven effective for studying the dynamics of breaking. The primary motivation for the research presented in this thesis was to determine whether measurements of the sound generated by breaking waves could be used to quantitatively study the dynamics of the breaking process.Laboratory measurements of the microwave backscatter and acoustic radiation from two-dimensional breaking waves are described in Chapter 2. The major findings of this Chapter are: 1) the mean square acoustic pressure and backscattered microwave power correlate with the wave slope and dissipation for waves of moderate slope, 2) the mean square acoustic pressure and backscattered microwave power correlate strongly with each other, and 3) the amount of acoustic energy radiated by an individual breaking event scaled with the amount of mechanical energy dissipated by breaking. The observed correlations with the mean square acoustic pressure are only relevant for frequencies greater than 2200 Hz because lower frequencies were below the first acoustic cut-off frequency of the wave channel.In order to study the lower frequency sound generated by breaking waves another series of two-dimensional breaking experiments was conducted. Sound at frequencies as low as 20 Hz was observed and the mean square acoustic pressure in the frequency band from 20 Hz-l kHz correlated strongly with the wave slope and dissipation. A characteristic low frequency signal was observed immediately following the impact of the plunging wave crest. The origin of this low frequency signal was found to be the pulsating cylinders of air which are entrained by the plunging waves. The pulsation frequency correlated with both the wave slope and dissipation. Following the characteristic constant frequency signal, approximately 0.25 s after the initial impact of 2 the plunging crest, another low frequency signal was typically observed. These signals were generally lower in frequency initially and then increased in frequency as time progressed.To determine if three-dimensional effects were important in the sound generation process and to measure the sound beneath larger breaking waves a series of experiments was conducted in a large multi-paddle wave basin. Three-dimensional breaking waves were generated and the sound produced by breaking was measured in the frequency range from 10 Hz to 20 kHz. 'The observed...

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confidence: 94%

Section: 21mentioning

confidence: 99%

Section: Chapter L; Microwaye Ilwl Acoustic Experimentsmentioning

confidence: 99%

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Laboratory measurements of the sound generated by breaking waves

Loewen¹

1991

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“…The relationship between the energy dissipated by breaking waves and the sound radiated was initially examined by Melville, Loewen, Felizardo, Jessup & Buckingham (1988) for controlled breaking waves in the laboratory. This experiment, as well as the subsequent investigation by Loewen & Melville (1991a) using a larger set of wave packets, established that over a limited range of parameters, the acoustic energy radiated by a breaking event is…”

Section: Breaking Wave Sound and Dissipationmentioning

confidence: 99%

“…(Farmer & Vagle, 1989). Laboratory experiments on breaking waves by Melville, Loewen, Felizardo, Jessup & Buckingham (1988) and by Loewen & Melville (1991a) suggest that the dissipation of surface wave energy in the ocean may also be inferred from measurements of ambient noise. This hypothesis is further explored in this work.…”

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Ambient noise and surface wave dissipation in the ocean

Felizardo¹

1993

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Bubble clouds and the dynamics of the upper ocean

Thorpe¹

1992

Quart J Royal Meteoro Soc

115

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Prcwlcntial addrc\\ dclivcrcd I Y Junc 19Y1) SIIMMAKYThis is a review of turbulence in the upper ocean close to the sea surface, particularly of the information that has been obtained from sonar observations of bubble clouds produced by breaking wind waves. These clouds provide tracers of the turbulent motions and are important, especially at high wind speeds, in the process of air-sea gas transfer. The observations of bubble clouds are here related to other measurements of turbulence, particularly to direct measurements of currents and temperatures in lakes or at sea, and to laboratory studies. Some novel observations of bubble clouds and breaking waves, their frequency and relation to Langmuir circulation, are presented.There is now emerging a pattern of clues that point to the dominance of breaking surface gravity waves as a source of turbulence to a depth below the surface of 0.04 to 0.2 times the wavelength of the dominant breaking waves, although the effect of swell has yet to be clarified. The relative depth appears to increase with increasing values of W,,,/c, where W,,, is the wind speed and c the phase speed of the dominant waves. Below this region the generation of turbulence may be dominated by shear-stresc or convection. Here. turbulence is generally similar to that in the atmospheric boundary layer. There are, however, coherent motions on the scale of the mixing layer that persist for periods of a few minutes to an hour or so, to which the transport of a large part of the momentum and heat fluxes can be attributed. and which strongly affect the dispersion of buoyant particles or bubbles. These motions deserve special study to establish their contribution to heat and momentum transport, and hence to determine if, or when, they should be specifically represented in models of the upper ocean devised, for example, to describe the dispersion of passive and non-passive tracers or the air-sea transfer of gases.

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Acoustic and microwave signatures of breaking waves

Cited by 64 publications

References 6 publications

Laboratory measurements of the sound generated by breaking waves

Laboratory measurements of the sound generated by breaking waves

Ambient noise and surface wave dissipation in the ocean

Bubble clouds and the dynamics of the upper ocean

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