An Autonomously Recording Inverted Echo Sounder: ARIES II

Thorpe, S. A.; Ulloa, Marco J.; Baldwin, D.; Hall, A. J.

doi:10.1175/1520-0426(1998)015<1346:aaries>2.0.co;2

Cited by 6 publications

(5 citation statements)

References 16 publications

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“…2) 11±13 . But, before modi®cation for sex recognition and mate attraction 13,14 , the second phase would have existed probably in some sexually monomorphic form. Furthermore, in other gymnotiform familiesÐsuch as Gymnotidae, Rhamphichthyidae and ApteronotidaeÐthis additional phase is present but not sexually dimorphic.…”

Section: Thus a Signalmentioning

confidence: 99%

“…The sonar beam pointing into the current shows the features to be drifting down-current through the beam at speeds of 0.8960.09 m s -1 . Such speeds are greater than that of the tidal current at 33 m depth (0.7560.02 m s -1 ) but less than that at 17 m depth(0.9860.03 m s -1 ); they are also less than the speeds of isolated bubble clouds (1.2960.08 m s -1 ) seen in the sonar image, which are characteristic of the wind drift and tidal current in the upper 1 m of the water column 9,13,16 .…”

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confidence: 95%

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Surface effects of bottom-generated turbulence in a shallow tidal sea

Smith

Thorpe

Graham

1999

Nature

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Turbulence in shelf seas strongly affects the spread of pollution (such as oil spills 1 ) as well as the distribution of sediment 2 and phytoplankton blooms 3 . Turbulence is known to be generated intermittently close to the sea bed 4 , but little is known of its evolution through the water column, or to what extent it affects the surface. Here we present observations of the surface effects of bottom-generated turbulence in a tidally in¯uenced and well mixed region of the North Sea, as derived from acoustic and visual images. Although the sea bed in the area is¯at, we ®nd that at any one time, 20±30% of the water surface is affected by boilsÐ circular regions of local upwellingÐof diameter 0.960.2 times the water depth. The signature of individual boils persists for at least 7 minutes and, in accordance with laboratory 5,6 and numerical 7 studies, shows the appearance of eddies. The boils contribute to the replacement of surface waters from depth in unstrati®ed waters, and may therefore enhance the¯uxes of gases between atmosphere and ocean.There are no reported observations of the surface signature of boils in well mixed, open sea. It is, however, clear from dynamical measurements made using current meters that tidal¯ows generate turbulence through the action of shear stress at the sea bed in much the same manner as in channels in laboratory experiments 4,8 . Fluid is intermittently ejected away from the bottom in turbulent bursts that may reach vertical speeds of 25% of the forcing current 4 . Numerical 7 and laboratory 5,6 studies show that the upwardmoving water produces a boil as it impinges on the water surface.Upward-pointing side-scan sonar has been used to observe a wide variety of processes in the upper ocean 9±13 . In experiments designed to study the processes leading to dispersion of an oil plume in the tidally well mixedÐand consequently unstrati®ed 14 Ðsouthern North Sea, a two-beam side-scan sonar system was mounted on a frame set on the sea bed at a depth of 45 m. The sonars operate at 80 kHz and 90 kHz, are set at 908 apart in the horizontal, and produce vertical fan-like beams with axes aligned upwards, 208 from the horizontal 15 . The site is 56 km from the shore and the local sea bed is¯at, with no sand banks or other notable bed forms. The principal acoustic scatterers are bubbles, of typical diameter 20± 200 mm, produced in clouds by wind waves as they break 16 . The clouds are detectable to ranges of ,150 m along the sea surface from the sonar, bubbles accumulating in regions of surface convergence and downwelling 17,18 . Oil reduces wave breaking and acoustic scatter from the sea surface 10 . Acoustic observations were made, however, at least 0.5 km from the oil plume, and in a variety of wind speeds from near calm to 14 m s -1 and in tidal currents reaching 1 m s -1 . letters to nature NATURE | VOL 400 | 15 JULY 1999 | www.nature.com 251 Figure 1 Sonar and video images of boils at the sea surface. The scale is the same in both images (and along both axes), and the tidal current is from ...

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Section: Thus a Signalmentioning

confidence: 99%

mentioning

confidence: 95%

Surface effects of bottom-generated turbulence in a shallow tidal sea

Smith

Thorpe

Graham

1999

Nature

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“…The depth and duration of bubble plumes in shallow and stratified systems can also be influenced by shear-driven turbulence that is generated at the seabed or across horizontal density surfaces [38]. It is unlikely that spilling waves can generate enough turbulence to sustain bubbles at depths far below the surface [40], and in short-fetch, high-current systems like PIR, bubble depth may closer reflect surface turbulence rather than the presence of large plunging waves. Indeed, model output confirmed that strong currents were correlated with deep entrainment of bubbles (Figures 4 and 5).…”

Section: Geophysical Controls On Bubble Plumesmentioning

confidence: 99%

“…Acoustic sensing methods have been frequently used to study subsurface bubble plumes formed by breaking waves in deep and open-ocean waters [35][36][37][38][39][40][41][42][43][44][45][46][47][48]. Recently, Vagle et al [49] and Wang et al [50] deployed acoustic instruments in continental shelf waters to characterize the static bubble cloud that persists below the water surface due to wave breaking during storms.…”

Section: Introductionmentioning

confidence: 99%

Bubble Clouds in Coastal Waters and Their Role in Air-Water Gas Exchange of CO2

Crosswell

2015

JMSE

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Abstract:Bubbles generated by breaking waves can drive significant gas exchange between the ocean and atmosphere, but the role of bubble-mediated gas transfer in estuaries is unknown. Here, backscatter data from 41 acoustic Doppler current profiler stations was analyzed to assess subsurface bubble distributions in nine estuaries along the U.S. East and Gulf Coast. Wind speed, wind direction, and current velocity were the dominant controls on bubble entrainment, but the relative importance of these physical drivers depended on local geomorphology. Bubble entrainment in high-current or shallow, long-fetch estuaries began at wind speeds <5 m s −1. In deep or fetch-limited estuaries, bubble entrainment was less frequent and generally began at higher wind speeds. Data observed during several storms suggests that episodic bubble-driven gas exchange may be an important component of annual CO2 fluxes in large, shallow estuaries but would be less significant in other coastal systems.

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“…These features or targets (e.g., label A) present hyperbolic range variations of few seconds, and the slope of the hyperbola asymptotes determines the targets' speed in the direction of sonar beams. From the geometry of orthogonal side-scan sonars (Thorpe et al 1998, Ulloa 2002, the mean phase speed and direction of propagation of the linear features are estimated to be (13.3 ± 4.5) m s −1 and (97 ± 18) • respectively. Consistency with linear theory of surface gravity waves is good.…”

Section: Surface Gravity Wavesmentioning

confidence: 99%

Interpreting underwater acoustic images of the upper ocean boundary layer

Ulloa¹

2007

Eur. J. Phys.

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A challenging task in physical studies of the upper ocean using underwater sound is the interpretation of high-resolution acoustic images. This paper covers a number of basic concepts necessary for undergraduate and postgraduate students to identify the most distinctive features of the images, providing a link with the acoustic signatures of physical processes occurring simultaneously beneath the surface of the sea. Sonars are so sensitive that they detected a new acoustic signature at the breaking of surface gravity waves in deep water, which resembles oblique motion-like vortices.

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An Autonomously Recording Inverted Echo Sounder: ARIES II

Cited by 6 publications

References 16 publications

Surface effects of bottom-generated turbulence in a shallow tidal sea

Surface effects of bottom-generated turbulence in a shallow tidal sea

Bubble Clouds in Coastal Waters and Their Role in Air-Water Gas Exchange of CO2

Interpreting underwater acoustic images of the upper ocean boundary layer

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