Measuring Turbulent Dissipation Using a Tethered ADCP

Abstract The structure function method for estimating the dissipation rate of turbulent kinetic energy, previously validated for measurements from seabed fixed mounts, is applied to data from 1.2-MHz acoustic Doppler current profiler (ADCP) instruments operating in pulse–pulse coherent mode and mounted in midwater below a tethered buoy. Movements of the buoy introduce additional relative velocity components, but it is hypothesized that these flow components should not seriously interfere with the turbulence information because (i) horizontal or vertical translation induces the same flow component in all cells of an ADCP beam and (ii) any rotation of the instrument about its center induces flow components that are normal to the beam direction, and thus neither affect the structure function. This hypothesis is tested by comparing a series of dissipation measurements from a moored ADCP with those from a free-falling Vertical Microstructure Profiler (VMP) shear probe deployed from a nearby research vessel. The results indicate generally good conformity in both mean and variability over almost two decades of dissipation rates. The noise level of the structure function estimates with the pulse–pulse coherent ADCP is close to that of the VMP at ~3 × 10−10 W kg−1. This approach offers the prospect of long time series measurements of dissipation rate from moorings, albeit with restricted vertical range of a few meters.

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Spectral and Structure Function Estimates of Turbulence Dissipation Rates in a High-Flow Tidal Channel Using Broadband ADCPs

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-16-0131.1 ◽

2017 ◽

Vol 34 (1) ◽

pp. 5-20 ◽

Cited By ~ 9

Author(s):

Justine M. McMillan ◽

Alex E. Hay

Keyword(s):

Structure Function ◽

Dissipation Rate ◽

Acoustic Doppler Current Profiler ◽

Universal Constant ◽

Flow Speed ◽

High Flow ◽

Small Scale ◽

Order Structure ◽

Tidal Channel ◽

Current Profiler

AbstractSpectral and structure function methods are implemented to compute the dissipation rate ε from broadband, diverging-beam acoustic Doppler current profiler (ADCP) data collected at four sites in a high-flow tidal channel. This paper shows that middepth estimates of ε obtained from spectral and second-order structure function (SF2) methods are both lognormally distributed with comparable means and variances. Speed bin–averaged ε values agree to within 16%, depending on the site and tidal phase (ebb/flood). The close agreement between the two independent methods provides further support for the argument put forward by McMillan et al.: that is, that the factor-of-2 difference between shear probe and (spectral) ADCP estimates of ε was likely caused by spatial differences in turbulence levels. The agreement between the spectral and both second- and third-order structure function methods also supports the use of for the SF2 universal constant. Notably, however, the SF3 method was less robust for these data. Two additional aspects of the SF2 approach are examined in some detail: 1) the differences from upstream- and downstream-facing beams are shown to arise from the Reynolds stress and 2) the inability of the ADCP to resolve small-scale motions does not affect the estimates of ε but yields apparent Doppler noise levels that—counterintuitively—decrease with increasing flow speed and increasing dissipation rate. A modified SF2 method that accounts for the variance associated with the unresolved scales removes the flow speed dependence and yields noise level estimates that agree with the spectral values.

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A Method for Processing Acoustic Doppler Current Profiler Velocity Data from Towed, Undulating Vehicles

Journal of Atmospheric and Oceanic Technology ◽

10.1175/2008jtecho534.1 ◽

2008 ◽

Vol 25 (9) ◽

pp. 1710-1716 ◽

Cited By ~ 1

Author(s):

Jiayi Pan ◽

David A. Jay

Keyword(s):

Surface Waters ◽

High Frequency ◽

Acoustic Doppler Current Profiler ◽

Small Time ◽

Ocean Current ◽

Near Surface ◽

Vertical Range ◽

External Reference ◽

Current Profiler ◽

Adcp Measurements

Abstract The utility of the acoustic Doppler current profiler (ADCP) for sampling small time and space scales of coastal environments can be enhanced by mounting a high-frequency (1200 kHz) ADCP on an oscillating towed body. This approach requires both an external reference to convert the measured shears to velocities in the earth coordinates and a method to determine the towed body velocities. During the River Influence on the Shelf Ecosystems (RISE) project cruise, a high-frequency (1200 kHz) and narrowbeam ADCP with mode 12 sampling was mounted on a TRIAXUS oscillating towfish, which steers a 3D path behind the ship. This deployment approach extended the vertical range of the ADCP and allowed it to sample near-surface waters outside the ship’s wake. The measurements from a ship-mounted 1200-kHz narrowbeam ADCP are used as references for TRIAXUS ADCP data, and a method of overlapping bins is employed to recover the entire vertical range of the TRIAXUS ADCP. The TRIAXUS vehicle horizontal velocities are obtained by removing the derived ocean current velocity from the TRIAXUS ADCP measurements. The results show that the method is practical.

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Temporal variations of zooplankton biomass in the Ligurian Sea inferred from long time series of ADCP data

Ocean Science ◽

10.5194/os-10-93-2014 ◽

2014 ◽

Vol 10 (1) ◽

pp. 93-105 ◽

Cited By ~ 13

Author(s):

R. Bozzano ◽

E. Fanelli ◽

S. Pensieri ◽

P. Picco ◽

M. E. Schiano

Keyword(s):

Time Series ◽

Acoustic Doppler Current Profiler ◽

Temporal Variations ◽

Zooplankton Biomass ◽

Mesopelagic Fish ◽

Ligurian Sea ◽

Time Frequency ◽

Backscattering Strength ◽

Current Profiler ◽

Long Time

Abstract. Three years of 300 kHz acoustic doppler current profiler data collected in the central Ligurian Sea are analysed to investigate the variability of the zooplankton biomass and the diel vertical migration in the upper thermocline. After a pre-processing phase aimed at avoiding the slant range attenuation, hourly volume backscattering strength time series are obtained. Despite the lack of concurrent net samples collection, different migration patterns are identified and their temporal variability examined by means of time–frequency analysis. The effect of changes in the environmental condition is also investigated. The highest zooplankton biomasses are observed in April–May just after the peak of surface primary production in March–April. The main migration pattern found here points to a "nocturnal" migration, with zooplankton organisms occurring deeper in the water column during the day and shallower at night. Also, twilight migration is highlighted during this study. The largest migrations are recorded in November–December, corresponding to lowest backscattering strength values and they are likely attributable to larger and more active organisms (i.e. euphausiids and mesopelagic fish). The results suggest further applications of the available historical acoustic doppler current profiler time series.

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Percampuran vertikal di Perairan Laut Maluku dan Talaud pada bulan Februari 2021

Oseanologi dan Limnologi di Indonesia ◽

10.14203/oldi.2021.v6i2.363 ◽

2021 ◽

Vol 6 (2) ◽

pp. 97

Author(s):

Adi Purwandana ◽

Mochamad Riza Iskandar ◽

Edi Kusmanto ◽

Muhammad Fadli ◽

Priyadi Dwi Santoso ◽

...

Keyword(s):

North Pacific ◽

Dissipation Rate ◽

Vertical Mixing ◽

Acoustic Doppler Current Profiler ◽

Core Layer ◽

Energy Dissipation Rate ◽

Intermediate Water ◽

North Pacific Intermediate Water ◽

Current Profiler ◽

Temperature Depth

Vertical mixing in the northern Maluku Sea and Talaud Waters in February 2021. The spatial variability of water mass mixing in the northern Maluku Sea and Talaud waters are presented based on the results of Eastern Indonesia Expedition (EIT) 2021 using RV Baruna Jaya VIII-LIPI. The turbulent kinetic energy dissipation rate was obtained using the Kunze-Williams-Briscoe (KWB) Method calculated from CTD (Conductivity, Temperature, Depth) and LADCP (Lowered Acoustic Doppler Current Profiler) datasets. We found the dissipation rate in the core layer of North Pacific Subtropical Water (NPSW) and North Pacific Intermediate Water (NPIW) are in the order of 10-6 W/kg and 10-8 W/kg, respectively. The KWB Method used in this study is also proven comparable with the Thorpe Method.

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Mixing and Entrainment in the Red Sea Outflow Plume. Part II: Turbulence Characteristics

Journal of Physical Oceanography ◽

10.1175/jpo2689.1 ◽

2005 ◽

Vol 35 (5) ◽

pp. 584-600 ◽

Cited By ~ 43

Author(s):

Hartmut Peters ◽

William E. Johns

Keyword(s):

Red Sea ◽

Sea Water ◽

Acoustic Doppler Current Profiler ◽

Bottom Layer ◽

Small Sample ◽

Interfacial Stress ◽

Salt Flux ◽

Turbulent Dissipation ◽

Eddy Diffusivities ◽

Current Profiler

Abstract South of the Strait of Bab el Mandeb, saline Red Sea Water flows downslope into the Gulf of Aden mainly along the narrow 130-km-long “Northern Channel” (NC) and the shorter and wider “Southern Channel” (SC). In the NC, the Red Sea plume simultaneously exhibited weak entrainment into a 35–120-m-thick, weakly stratified bottom layer while a 35–285-m-thick interfacial layer above showed signs of vigorous mixing, overturns up to 30 m thick, and extensive zones of gradient Richardson numbers below 1/4. Turbulent overturning scales, or Thorpe scales, are extracted from regular CTD profiles and equated to Ozmidov scales. On this basis, interfacial mixing is quantified in terms of estimated turbulent dissipation rates, vertical turbulent salt flux, and interfacial stress. Even though these estimates are subject to significant uncertainty, they demonstrate the intensity of mixing during strong winter outflow in terms of eddy diffusivities Kρ on the order of 10−2 m2 s−1. The large Kρ occur in strong stratification such that vertical turbulent salt fluxes are also large. Along the NC, relative maxima of Kρ correspond to maxima in the bulk Froude number. Direct short-term measurements of the Reynolds stress just above the seafloor at two locations, one in the NC and one in the SC, allow comparisons of the bottom stress τb with the interfacial turbulent stress τi. The ratio τi/τb shows large scatter in a small sample, with maximum values on the order of 1. An appendix outlines procedures of making and reducing lowered acoustic Doppler current profiler measurements optimized for observing descending plumes.

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Resolving velocity ambiguity of two coded pulse in broad-band acoustic Doppler current profiler

MATEC Web of Conferences ◽

10.1051/matecconf/201928307013 ◽

2019 ◽

Vol 283 ◽

pp. 07013

Author(s):

Weixuan Zhang ◽

Changhong Wang ◽

Kai Deng

Keyword(s):

Measurement Accuracy ◽

Time Lag ◽

Broad Band ◽

Acoustic Doppler Current Profiler ◽

Short Sequence ◽

Measurable Velocity ◽

Numerous Experimental Data ◽

Current Profiler ◽

Long Time ◽

Short Time

Broad-band Acoustic Doppler Current Profiler (BBADCP) adopts short-sequence coded pulse to measure high velocity. Short-sequence coded pulse has large measurable velocity, so it is not easy to have velocity ambiguity. But short coded pulse deteriorates the accuracy of the velocity. To obtain more accurate velocity, we adopt two coded pulse with a time lag. This paper analyzes the ambiguity velocity and velocity standard deviation of two coded pulse and single coded pulse, and gives a solution to resolve velocity ambiguity: single coded pulse which has a large ambiguity velocity due to the short time lag is used to establish a coarse estimate of the velocity, two coded pulsewhich has a long time lag is used to have a high accuracy velocity, then we combine the two velocities in a way to provide an accurate velocity. It has been demonstrated that the two coded pulse can reduce variance of velocity through analyzing numerous experimental data of pool. Meanwhile, the efficiency of method to solve ambiguity has been proved in accordance with multiple sets of data. Compared with the traditional methods, this method has good anti-noise performance and high single measurement accuracy.

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