Laboratory Comparisons of Acoustic and Optical Sensors for Microbubble Measurement

Su, Ming Vang; Todoroff, Douglas G.; Cartmill, John

doi:10.1175/1520-0426(1994)011<0170:lcoaao>2.0.co;2

Cited by 29 publications

(18 citation statements)

References 1 publication

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“…The difference seems to be related to the absence of bubble coalescence in salt water, due to organic active materials which are able to reduce the surface tension and to prevent thin films from rupturing (Kitchener, 1964) or to electric repulsion between bubbles due to the preferential ions deposition over the surface (Pounder, 1986). In addition, Su et al (1994) recorded high void fractions, up to 60% at a depth of 25 cm and wind speed of 15 m/s. A significant fraction, from 30% to 50%, of the energy dissipated during breaking is work against buoyancy.…”

Section: The Effect Of Air Entrapmentmentioning

confidence: 98%

Turbulence in the swash and surf zones: a review

Longo

Petti

Losada

2002

Coastal Engineering

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This paper reviews mainly conceptual models and experimental work, in the field and in the laboratory, dedicated during the last decades to studying turbulence of breaking waves and bores moving in very shallow water and in the swash zone. The phenomena associated with vorticity and turbulence structures measured are summarised, including the measurement techniques and the laboratory generation of breaking waves or of flow fields sharing several characteristics with breaking waves. The effect of air entrapment during breaking is discussed. The limits of the present knowledge, especially in modelling a two-or three-phase system, with air and sediment entrapped at high turbulence level, and perspectives of future research are discussed. D

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Section: The Effect Of Air Entrapmentmentioning

confidence: 98%

Turbulence in the swash and surf zones: a review

Longo

Petti

Losada

2002

Coastal Engineering

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“…Characteristics of natural bubble populations-Despite application of various techniques, including holography (O'Hern et al 1988), optical reflection (Su et al 1988), sound speed (Farmer and Vagle 1989), or acoustic backscatter (Vagle and Farmer 1992), the minimum bubble size for a bubble population observed to date in the ocean is ϳ10 m. This, however, should be interpreted as a resolution limit of the instruments. Holography could not distinguish a bubble from a particle Ͻ10 m (O'Hern et al 1988).…”

Section: Theory and Backgroundmentioning

confidence: 99%

“…Holography could not distinguish a bubble from a particle Ͻ10 m (O'Hern et al 1988). The linearity of the calibration curve used for the optical reflection method (Su et al 1988) is valid only for bubbles Ͼ10 m (Su et al 1994). The acoustic resonance frequency for a 10-m bubble is ϳ325 kHz at the surface and will increase with depth (Clay and Medwin 1977).…”

Section: Theory and Backgroundmentioning

confidence: 99%

The volume scattering function of natural bubble populations

Zhang

Lewis

Lee

et al. 2002

Limnology & Oceanography

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The volume scattering function (VSF) of natural bubble populations is (1) determined from Mie scattering theory, (2) measured by a newly designed volume scattering meter in the laboratory, and (3) inferred from field observations of the VSF. The laboratory measurements have confirmed our theoretical prediction in that (1) bubbles of sizes that have been recorded in situ in the surface ocean (Ͼ10 m) show elevated scattering for angles between 60Њ and 80Њ and (2) the organic coatings on the bubble surface will increase the scattering in the backward hemisphere but little change the scattering in the forward directions, including the critical angles. An optimization analysis is applied to the measurement of the VSF in coastal waters, and the results suggest the potential existence of submicron bubbles that are coated with organic film. The bubble population thus determined, which has a negligible contribution to the total scattering (5%), accounts for 40% of the total backscattering that has been observed in situ. The extension of the bubble size distribution to smaller sizes than can presently be measured by direct techniques will alter the shape of derived phase function in general but will result in rather small changes to the backscattering ratio (Ͻ20%) as long as the slope of the size distribution is small, because most of the changes are in the forward (Ͻ10Њ) direction. However, the prominent peak in the VSF at the critical angle observed for larger bubbles is strongly reduced by the inclusion of the small sizes, and the backscattering ratio is increased by a factor of two for distributions that varies as the Ϫ4 power of size. Because these bubbles contribute strongly to scattering at large angles, these results have significant implications for the remote observation of the color of the sea.Remote observations of the spectral distribution of light backscattered from the upper ocean provide the only practical means for diagnosing the spatial and temporal varia-

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“…Determination of both the acoustic phase speed and attenuation by bubbly water was accomplished by the measurement of sound propagation across a fixed pathlength as well as the interpretation of the spectral response of a flooded acoustical resonator. One result of their efforts has been the sub-sequent refinement of a number of their techniques by other investigators (Su et al 1994;Lamarre and Melville 1995;Farmer and Vagle 1997) as newer technology, advanced signal processing techniques, and improved acoustic inversion schemes have become available. The work of Farmer and Vagle (1997) on Medwin's original resonator design has resulted in a number of improvements, including the removal of hydrostatic pressure effects through the use of PVDF transducers and the implementation of real-time processing that allows data acquisition at rates of O(1) Hz.…”

Section: Introductionmentioning

confidence: 99%

A broadband acoustic technique for measuring bubble size distributions

Terrill

Melville

1996

The Journal of the Acoustical Society of America

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The development of a broadband sound velocimeter that allows the simultaneous measurement of sound speed and attenuation over a wide range of frequencies is described. The velocimeter measures the attenuation and dispersion of a broadband acoustic pulse over frequencies ranging from 4 to 100 kHz across a fixed pathlength using a two-transducer system. The resulting data are inverted to arrive at bubble size distributions over bubble radii in the range 30-800 m.The instrument was tested in the large wave channel at the Hydraulics Laboratory of Scripps Institution of Oceanography. The channel can generate breaking waves of O(1 m) height using a hydraulically driven wave generator, giving bubble size distributions similar to those found in the field. The presence of the bubbles significantly changes the acoustical properties of the water. Internal consistency checks of the acoustic data and measurements of bubbles using an independent optical sizing technique support the accuracy of the acoustic system in measuring bubble size distributions.A field test of the system was performed off Scripps Pier in water of approximately 6-m depth. Observations demonstrate that bubble transport events with significant temporal and spatial variability are associated with rip currents and introduce significant vertical gradients in the acoustical properties of the water. The performance of the system in the field was found to be comparable to that found in the laboratory.

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Laboratory Comparisons of Acoustic and Optical Sensors for Microbubble Measurement

Cited by 29 publications

References 1 publication

Turbulence in the swash and surf zones: a review

Turbulence in the swash and surf zones: a review

The volume scattering function of natural bubble populations

A broadband acoustic technique for measuring bubble size distributions

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