A comparison of acoustic turbulence profiling techniques in the presence of waves

Whipple, Anthony C.; Luettich, Richard A.

doi:10.1007/s10236-009-0208-3

Cited by 8 publications

(5 citation statements)

References 16 publications

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“…The structure function takes the form

D true(z, r, t true) = C ϵ {true(z, t true)}^{2 / 3} r^{2 / 3}

in the inertial subrange, where

C = 2.0

is an empirical constant [ Pope , ]. The structure function has thus far only been applied to oceanic environments in water depths greater than several meters such as tidal channels, river mouths, and dense bottom plumes [ Wiles et al ., ; Mohrholz et al ., ; Whipple and Luettich , ].…”

Section: Methodsmentioning

confidence: 99%

Near‐bed turbulence dissipation measurements in the inner surf and swash zone

Lanckriet

Puleo

2013

JGR Oceans

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[1] Near-bed turbulence dissipation rates were quantified in the swash zone and inner surf zone of a dissipative beach. The vertical structure and temporal evolution of the dissipation rate were calculated using the structure function applied to profiles of the vertical velocity collected by three profiling acoustic Doppler velocimeters. Dissipation rates between 6 Á 10 25 m 2 =s 3 and 8 Á 10 23 m 2 =s 3 were observed. Turbulence dissipation rates increased with diminishing water depth but showed no significant correlation to offshore wave height. Temporal phasing of strong turbulence dissipation events agreed well with image-based observations of pixel intensity associated with wave breaking. Bore-generated turbulence decayed rapidly following bore arrival and followed a decay rate similar to grid turbulence. The turbulence dissipation was dominated by (advected) bore-generated turbulence during the uprush and initial stages of the backwash, and by bed-generated turbulence during the later stages of the backwash. A scaling analysis shows that near the bed, sediment-induced density stratification effects may have been an order of magnitude larger than turbulence dissipation.Citation: Lanckriet, T., and J. A. Puleo (2013), Near-bed turbulence dissipation measurements in the inner surf and swash zone,

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“…The structure function takes the form

D true(z, r, t true) = C ϵ {true(z, t true)}^{2 / 3} r^{2 / 3}

in the inertial subrange, where

C = 2.0

Section: Methodsmentioning

confidence: 99%

Near‐bed turbulence dissipation measurements in the inner surf and swash zone

Lanckriet

Puleo

2013

JGR Oceans

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“…If the flow is sheared, a proportion of the associated non-turbulent velocity difference between bins is unavoidably retained, contributing to the structure function and biassing the resulting ε estimates. This is similar to the effect of the vertical gradient of the orbital velocity forced by surface gravity waves, which can lead to non-turbulent velocity differences between bins being retained in the structure function and potential bias in ε estimates (Whipple and Luettich, 2009;Scannell et al, 2017).…”

Section: Introductionmentioning

confidence: 69%

Impact of acoustic Doppler current profiler (ADCP) motion on structure function estimates of turbulent kinetic energy dissipation rate

2022

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Abstract. Turbulent mixing is a key process in the transport of heat, salt, and nutrients in the marine environment, with fluxes commonly derived directly from estimates of the turbulent kinetic energy dissipation rate, ε. Time series of ε estimates are therefore useful in helping to identify and quantify key biogeochemical processes. The velocity structure function method can be used to determine time series of ε estimates using along-beam velocity measurements from suitably configured acoustic Doppler current profilers (ADCPs). Shear in the background current can bias such estimates; therefore, standard practice is to deduct the mean or linear trend from the along-beam velocity over the period of an observation burst. This procedure is effective if the orientation of the ADCP to the current remains constant over the burst period. However, if the orientation of the ADCP varies, a proportion of the velocity difference between bins is retained in the structure function and the resulting ε estimates will be biased. Long-term observations from a mooring with three inline ADCPs show the heading oscillating with an angular range that depends on the flow speed: from large, slow oscillations at low flow speeds to smaller, higher-frequency oscillations at higher flow speeds. The mean tilt was also determined by the flow speed, whilst the tilt oscillation range was primarily determined by surface wave height. Synthesised along-beam velocity data for an ADCP subject to sinusoidal oscillation in a sheared flow indicate that the retained proportion of the potential bias is primarily determined by the angular range of the oscillation, with the impact varying between beams depending on the mean heading relative to the flow. Since the heading is typically unconstrained in a tethered mooring, heading oscillation is likely to be the most significant influence on the retained bias for a given level of shear. Use of an instrument housing designed to reduce oscillation would mitigate the impact, whilst if the shear is linear over the observation depth range, the bias can be corrected using a modified structure function method designed to correct for bias due to surface waves.

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“…If the flow is sheared, a proportion of the associated non-turbulent velocity difference between bins us unavoidably retained, contributing to the structure function and biasing the resulting ε estimates. This is similar to the effect of the vertical gradient of the orbital velocity forced by surface gravity waves, which can lead to non-turbulent velocity differences between bins being retained in the structure function and potential bias in ε estimates (Whipple and Luettich, 2009;Scannell et al, 2017).…”

Section: Introductionmentioning

confidence: 69%

Impact of ADCP motion on structure function estimates of turbulent kinetic energy dissipation rate

Scannell

Lenn

Rippeth

2021

Preprint

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Abstract. Turbulent mixing is a key process in the transport of heat, salt and nutrients in the marine environment, with fluxes commonly derived directly from estimates of the turbulent kinetic energy dissipation rate, ϵ. Time series of ϵ estimates are therefore useful in helping to identify and quantify key biogeochemical processes. Estimates of ϵ are typically derived using shear microstructure profilers, which provide high resolution vertical profiles, but require a surface vessel, incurring costs and limiting the duration of observations and the conditions under which they can be made. The velocity structure function method can be used to determine time series of ϵ estimates using along-beam velocity measurements from suitably configured acoustic Doppler current profilers (ADCP). Shear in the background current can bias such estimates, therefore standard practice is to deduct the mean or linear trend from the along-beam velocity over the period of an observation burst. This procedure is effective if the orientation of the ADCP to the current remains constant over the burst period. However, if the orientation of a tethered ADCP varies, a proportion of the velocity difference between bins is retained in the structure function and the resulting ϵ estimates will be biased. Long-term observations from a mooring with three inline ADCP show the heading oscillating with an angular range that depends on the flow speed; from large, slow oscillations at low flow speeds to smaller, higher frequency oscillations at higher flow speeds. The mean tilt was also determined by the flow speed, whilst the tilt oscillation range was primarily determined by surface wave height. Synthesised along-beam velocity data for an ADCP subject to sinusoidal oscillation in a sheared flow indicates that the retained proportion of the potential bias is primarily determined by the angular range of the oscillation, with the impact varying between beams depending on the mean heading relative to the flow. Since the heading is typically unconstrained in a tethered mooring, heading oscillation is likely to be the most significant influence on the retained bias for a given level of shear. Use of an instrument housing designed to reduce oscillation would mitigate the impact, whilst if the shear is linear over the observation depth range, the bias can be corrected using a modified structure function method designed to correct for bias due to surface waves.

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A comparison of acoustic turbulence profiling techniques in the presence of waves

Cited by 8 publications

References 16 publications

Near‐bed turbulence dissipation measurements in the inner surf and swash zone

Near‐bed turbulence dissipation measurements in the inner surf and swash zone

Impact of acoustic Doppler current profiler (ADCP) motion on structure function estimates of turbulent kinetic energy dissipation rate

Impact of ADCP motion on structure function estimates of turbulent kinetic energy dissipation rate

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