Obtaining absolute water velocity profiles from glider-mounted Acoustic Doppler Current Profilers

Ordonez, Christopher E.; Shearman, R. Kipp; Barth, John A.; Welch, P. G.; Erofeev, A.; Kurokawa, Zen

doi:10.1109/oceans-yeosu.2012.6263582

Cited by 9 publications

(7 citation statements)

References 5 publications

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“…The 600-kHz ADCPs on John and June were set to 4-m vertical bins and 10-s ensembles sampling at about 1 Hz. Absolute velocity profiles were computed from all the velocity measurements between glider surfacings (Ordonez et al 2012).…”

Section: Discussion and Summarymentioning

confidence: 99%

The LatMix Summer Campaign: Submesoscale Stirring in the Upper Ocean

Shcherbina

Sundermeyer

Kunze

et al. 2015

Bulletin of the American Meteorological Society

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104

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Lateral stirring is a basic oceanographic phenomenon affecting the distribution of physical, chemical, and biological fields. Eddy stirring at scales on the order of 100 km (the mesoscale) is fairly well understood and explicitly represented in modern eddy-resolving numerical models of global ocean circulation. The same cannot be said for smaller-scale stirring processes. Here, the authors describe a major oceanographic field experiment aimed at observing and understanding the processes responsible for stirring at scales of 0.1–10 km. Stirring processes of varying intensity were studied in the Sargasso Sea eddy field approximately 250 km southeast of Cape Hatteras. Lateral variability of water-mass properties, the distribution of microscale turbulence, and the evolution of several patches of inert dye were studied with an array of shipboard, autonomous, and airborne instruments. Observations were made at two sites, characterized by weak and moderate background mesoscale straining, to contrast different regimes of lateral stirring. Analyses to date suggest that, in both cases, the lateral dispersion of natural and deliberately released tracers was O(1) m2 s–1 as found elsewhere, which is faster than might be expected from traditional shear dispersion by persistent mesoscale flow and linear internal waves. These findings point to the possible importance of kilometer-scale stirring by submesoscale eddies and nonlinear internal-wave processes or the need to modify the traditional shear-dispersion paradigm to include higher-order effects. A unique aspect of the Scalable Lateral Mixing and Coherent Turbulence (LatMix) field experiment is the combination of direct measurements of dye dispersion with the concurrent multiscale hydrographic and turbulence observations, enabling evaluation of the underlying mechanisms responsible for the observed dispersion at a new level.

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Section: Discussion and Summarymentioning

confidence: 99%

The LatMix Summer Campaign: Submesoscale Stirring in the Upper Ocean

Shcherbina

Sundermeyer

Kunze

et al. 2015

Bulletin of the American Meteorological Society

Self Cite

104

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“…The method used was based on the inversion routine described by Visbeck [5], for inversion of lowered CTD-mounted ADCP (LADCP) data. Key differences between LADCP and glidermounted ADCP data make direct application of LADCP software and methods difficult [7]. Velocity inversion involves simultaneous solution of a set of linear equations incorporating vertical shear derived from water profile data, bottom track data, and independent estimates of vehicle speed through water.…”

Section: Instruments and Sampling Parametersmentioning

confidence: 99%

Evaluations of a 600 kHz RDI phased array system ADCP and a wave module operating on a G2 Slocum glider

Pettigrew

Neary

Fleming

et al. 2014

2014 Oceans - St. John's

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“…One alternate method of obtaining current velocity from gliders is the "shear method". Ordonez et al, (2012) calculate a shear value from raw velocity measurements for each depth bin over a dive. They then integrate this value and reference it with vertically averaged currents to obtain a depth-resolved velocity profile.…”

Section: Introductionmentioning

confidence: 99%

“…They then integrate this value and reference it with vertically averaged currents to obtain a depth-resolved velocity profile. Though the method is promising, when compared with coincident bottom-track-reference velocities, an offset of 1-50 cm s -1 is observed; comparisons with a nearby research vessel showed similar differences (Ordonez et al, 2012). In this paper we use the methods developed by Todd et al (2011) andVisbeck (2002) to estimate depth-resolved currents from gliders with externally mounted, upward-looking ADCPs.…”

Section: Introductionmentioning

confidence: 99%

Improved methods to calculate depth-resolved velocities from glider-mounted ADCPs

Ellis

Washburn

Ohlmann

et al. 2015

2015 IEEE/OES Eleveth Current, Waves and Turbulence Measurement (CWTM)

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Ocean gliders are autonomous underwater vehicles typically used to sample spatial variations in scalar variables (e.g., temperature, salinity, and bio-optical water properties) along transects. More recently, gliders have been equipped with ADCPs for measuring current profiles along transects. Accurate measurement of velocity profiles from a moving platform requires knowledge of the platform motion over the earth. Determination of glider motion over the earth relies on glider GPS positions available only at times of glider surfacing. Glider surfacing intervals typically range from 10's of minutes to hours, precluding accurate instantaneous knowledge of glider motion. This is a major challenge for measuring velocity profiles from ocean gliders.One approach for determining vertical velocity profiles from glider-mounted ADCPs relies on estimating depth-integrated currents averaged between glider surfacings. Once estimated, vertically averaged velocity can be combined with horizontal glider velocities relative to the water to obtain depth-resolved velocities using methods of Visbeck (2001) and Todd et al. (2011). The vertically averaged velocity is calculated from the distance the glider strays from its projected position during the time between surfacings. This distance is computed as the difference between the dead-reckoned surfacing location and the actual surfacing location as measured by GPS. There are numerous methods for computing the dead-reckoned position of glider surfacings, but these have not been evaluated to determine which best predicts surfacing locations.Here, three methods for calculating vertically averaged horizontal current velocities from gliders are evaluated. Two Slocum Coastal G1 gliders (manufactured by Teledyne Webb Research), each with an upward looking 1 MHz ADCP (manufactured by Teledyne RD Instruments), were deployed off the California coast during the summer of 2012. The gliders flew 500 m square patterns around a bottom-mounted, upward-looking 600 kHz ADCP (manufactured by Teledyne RD Instruments) moored at a depth of 26 m. The moored ADCP data are key to evaluating methods for computing vertically averaged velocity from gliders and ultimately assessing depth-resolved current velocities obtained from glider-mounted ADCPs.The first method calculates the glider's horizontal velocity using pitch and vertical velocity. Vertical velocity is calculated by taking the derivative of pressure with respect to time. It is often assumed that the flight path is in the direction of the glider's long axis and α, the angle of attack or the angle between the glider's path through the water and its long axis, is zero. This assumption can result in errors of 2.5 cm s -1 (Merckelbach et al. 2001) which are on the order of 10% of the horizontal velocity. Previous studies have estimated angle of attack (e.g. Sherman et al. 2001) using model results for internally-mounted ADCPs on Spray gliders. The gliders in this study carried externally-mounted ADCPs, so errors may also result from extra drag and non-zer...

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Obtaining absolute water velocity profiles from glider-mounted Acoustic Doppler Current Profilers

Cited by 9 publications

References 5 publications

The LatMix Summer Campaign: Submesoscale Stirring in the Upper Ocean

The LatMix Summer Campaign: Submesoscale Stirring in the Upper Ocean

Evaluations of a 600 kHz RDI phased array system ADCP and a wave module operating on a G2 Slocum glider

Improved methods to calculate depth-resolved velocities from glider-mounted ADCPs

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