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Ming Li, Svein Vagle, and David M. Farmer

mechanically driven system with four sidescan sonars, Farmer and Li (1995) examined time sequences of horizontal backscatter images and found that some bubble bands join together to form Y-shaped junctions at high winds. These acoustic measurements capture the spatial structures and temporal evolutions of turbulence flows in the OML and provide useful data for comparing with LES simulation results. Smith (1992) observed a rapid evolution of LC from small to large scales, following a sudden increase in

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Maxim Nikurashin and Raffaele Ferrari

motions are very efficient at radiating waves from small topographic features, resulting in local mixing. Polzin and Firing (1997) also found that abyssal mixing appears to be enhanced in regions of strong geostrophic flows. Here, we test the hypothesis that the abyssal mixing observed in the Southern Ocean can be explained by radiation and breaking of waves resulting from geostrophic flows impinging on small-scale topography. Estimates of turbulent mixing inferred from lowered acoustic Doppler

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Brian D. Dushaw

the low-resolution computation. For the large-scale average metrics employed for this study, the responses of the uncertainties to the different measurement configurations are therefore likely to be about the same for the low- and high-resolution ocean state estimates. Two common objections to employing acoustic tomography are its possible effects on marine life and its costs, but these objections are specious. These two issues are addressed in turn. The 1996–2006 ATOC program included a

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Kjersti Bruserud and Sverre Haver

late 1990s onward, newly developed acoustic instruments have to a large extent taken over for mechanical current meters for current velocity measurements. When new instruments are to replace older, proven technologies, it is particularly important to test the performance of the current meters. This is most conveniently done by ensuring a certain amount of overlapping data from the different instruments. In addition, confidence in current measurements performed with different instruments and

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Dorian Cazau, Julien Bonnel, Joffrey Jouma’a, Yves le Bras, and Christophe Guinet

prospecting, oil and gas surveys) ( Knudsen et al. 1948 ; Wenz 1962 ). All these sources contribute conjointly to the noise spectrum characteristics (e.g., pressure level, spectral slope) in varying degrees, depending on their strength and conditions prevailing at the measurement location. Thus, the underwater ambient sound field contains quantifiable information about the physical and biological marine environment. To extract this information, passive acoustic systems have been used for monitoring

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Pierre Cauchy, Karen J. Heywood, Nathan D. Merchant, Bastien Y. Queste, and Pierre Testor

autonomous underwater vehicles, carrying sensors to monitor the ocean. They perform long autonomous missions (several months to a year, and several thousand kilometers) and provide high-resolution (~2 h, 2 km) hydrographic profiles ( Testor et al. 2010 ; Rudnick 2016 ). Glider measurements are not affected by extreme weather events. Their unique way of moving through the water column (buoyancy driven with no propellers) makes them extremely quiet and therefore very suitable for passive acoustic

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Levi F. Kilcher, Jim Thomson, Samuel Harding, and Sven Nylund

1. Introduction Acoustic Doppler velocimeters (ADVs) have been used to make high-precision measurements of water velocity for over 20 years ( Kraus et al. 1994 ; Lohrmann et al. 1995 ). During that time, they have been deployed around the world to measure turbulence from a range of platforms, including in the laboratory setting ( Voulgaris and Trowbridge 1998 ); from stationary structures on ocean, river, and lake bottoms ( Kim et al. 2000 ; Lorke 2007 ; Cartwright et al. 2009 ); in surface

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Katy L. Sheen, Nicky White, C. P. Caulfield, and Richard W. Hobbs

distribution that is derived from conductivity–temperature–depth (CTD) measurements (e.g., Arhan et al. 2002 ; Sherwin et al. 2008 ). Beneath the sea surface, geostrophic calculations are limited by restricted spatial sampling. Seismic reflection profiling is an important method for imaging thermohaline fine structure down to abyssal depths (e.g., Holbrook et al. 2003 ). During acquisition, acoustic energy generated by an array of air guns is reflected at boundaries within the water column where changes

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André Amador, Sergio Jaramillo, and Geno Pawlak

time-averaged ( –2.5 min), fixed ADCP measurements. Ensemble-averaged velocity differences calculated in a cross- and along-track reference frame, and obtained in a range of wave conditions confirm the presence of a wave-induced bias consistent with theory but also reveal an additional, persistent bias in the direction of the vehicle motion that is unaccounted for by wave effects. It is speculated that the unexplained residual may be associated with acoustic ringing effects. Together, the bias

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Stuart Bradley, Sabine von Hünerbein, and Torben Mikkelsen

4 min. Fig . 2. Dual bistatic geometry of Risø-78. Fig . 3. Comparison between mast (circles) and bistatic sodar measurements (triangles) from the Risø-78 experiment (adapted from Underwood 1981 ). Mastrantonio et al. (1986) also presented some preliminary results such as the use of a staring-mode bistatic sodar that could be used simultaneously with a three-axis monostatic sodar, and Mathews et al. (1986) explored refractive acoustic path bending effects for bistatic sodars. Moulsley and

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