Acoustic Doppler current profiler performance in near surface and bottom boundaries

Appell, G.; Bass, Polly; Metcalf, Michael A.

doi:10.1109/48.90903

Cited by 19 publications

(12 citation statements)

References 2 publications

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“…This noise complicated the identification of a diurnal signal in the hourly velocity record (Figures 2d and 2e), requiring the use of the composites and averaging in the analyses described below. The shallow limit of the upward-looking ADCP profile is set by sidelobe interference from the surface (Appell et al, 1991), and thus depends on how shallow the ADCP instrument was mounted; for these sites, the shallowest usable data occurred around 11-m depth. Velocity data were leveled using pressure measured at the ADCP instrument and interpolated to a fixed 2-m vertical grid.…”

Section: Data Processingmentioning

confidence: 99%

Diurnal Cycles of Near‐Surface Currents Across the Tropical Pacific

et al. 2021

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The diurnal cycle of solar heating modulates the penetration of heat and momentum into the ocean interior. Daytime heating creates warm stratified layers in the upper few meters at the ocean surface, called the diurnal warm layer (DWL). Nighttime cooling destroys the DWL and transmits the heat in these warm layers downward via convective mixing. When wind blows over the warm afternoon ocean, wind momentum can be trapped and concentrated in this buoyantly isolated warm layer. Especially in the tropics, where Coriolis turning is weak, this layer can thus form a diurnal jet: a localized wind-driven current that forms at the ocean surface each afternoon.The diurnal warm layer in the top few meters of the afternoon ocean can be several degrees warmer than the bulk SST (Ward, 2006); thus the DWL plays an important, widespread role in setting heat flux between the ocean and the atmosphere (

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Section: Data Processingmentioning

confidence: 99%

Diurnal Cycles of Near‐Surface Currents Across the Tropical Pacific

et al. 2021

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“…Data obtained when the ship was turning or accelerating were eliminated from our analysis by screening out data acquired when the ship speed was less than 1.5 m s −1 . We also eliminated observations from the bottom 10% of the water column where bias resulting from the bottom reflection of the acoustic sidelobe occurs [ Appell et al ., ]. East and north velocity components were rotated to a coordinate system oriented 30° to the north of east (a direction consistent with the orientation of the tidal major axis in the western sound) to produce along‐estuary and across‐estuary components.…”

Section: Observationsmentioning

confidence: 99%

Residual circulation in western Long Island Sound

2013

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[1] Current, salinity and temperature measurements from repeated ship transects, complemented by observations from long duration current profilers, are used to characterize the variability and structure of subtidal flow in western Long Island Sound, a region prone to seasonal hypoxia. Subtidal flow plays a leading role in the transport of oxygen and organic matter and must, therefore, be simulated as accurately as possible. We show that during periods of light wind in March and July, the subtidal along-sound flow is vertically and horizontally sheared with lower salinity water in the top 7 m moving eastward toward the ocean at approximately 10 cm s À1 with a counterflow of similar magnitude elsewhere. Velocity contours were found to slope downward to the south, and maximum eastward velocities were found near the surface on the southern half of the section. We find that there is a net transport in the direction of the East River (westward.) The velocity distribution is broadly consistent with theoretical predictions for the steady, frictional, baroclinic pressure gradient driven flow modified by Coriolis acceleration, despite its neglect of advective effects which were found to be important in the present observational analysis. Our estimates of the pressure gradient, the Coriolis acceleration and stress divergence have similar magnitudes. Observation-based estimates of terms in the momentum balance suggest that advection is more important to along-estuary momentum than across-estuary momentum. Along-estuary advection is overestimated in recent hydrodynamic simulations when compared to observed values at sampling locations.

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“…Acoustic Doppler current profilers (ADCP) do not provide reliable water velocity measurements near the sea surface or bottom because acoustic sidelobe reflections from the boundary contaminate the Doppler velocity measurements (Appell et al 1991). Even though the acoustic sidelobes are much weaker than the main beams (e.g., Appell et al 1991;Gordon 1996), the surface reflection is ∼40 dB (or 100 times) stronger than from particles in the water. Consequently, sidelobe reflections from the surface can be as strong as the main beam returns from the water column.…”

Section: Introductionmentioning

confidence: 99%

“…Consequently, sidelobe reflections from the surface can be as strong as the main beam returns from the water column. As a result, acoustic returns from the main beams are only useful for calculating currents prior to the arrival of the vertical sidelobe reflection from the sea surface (Appell et al 1991;Gordon 1996). From the ADCP beam geometry (Fig.…”

Section: Introductionmentioning

confidence: 99%

“…Experience indicates that sidelobe contamination extends farther below the sea surface than z sl , often by a factor of 2 (e.g., Appell et al 1991;Teague et al 2001) Yet there is no consistent criteria for determining the near-surface region contaminated by the sidelobe reflection and a percentage of the range to the surface greater than 6% is often used (e.g., Kirincich et al 2005;Fewings et al 2008;Kirincich and Lentz 2017). The extension of the sidelobe contamination below z sl is commonly attributed to the effects of surface gravity waves, as their time-varying surface reflections are normally smeared over a number of depth bins within the ensemble averaging normally employed with ADCP sampling.…”

Section: Introductionmentioning

confidence: 99%

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A Note on the Depth of Sidelobe Contamination in Acoustic Doppler Current Profiles

Lentz

Kirincich

Plueddemann

2022

Journal of Atmospheric and Oceanic Technology

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Acoustic Doppler current profilers (ADCP) do not provide reliable water velocity measurements near the sea surface or bottom because acoustic side-lobe reflections from the boundary contaminate the Doppler velocity measurements. The apparent depth of the center of the side-lobe reflection is zsl = ha(1 − cos(θ)) where ha is the distance from the ADCP acoustic head to the sea surface and θ is the ADCP beam angle. However, side-lobe contamination extends one and a half ADCP bins below zsl as the range gating of the acoustic return causes overlap between adjacent ADCP bins. Consequently the contaminated region z < zsl + 3Δz/2 is deeper than traditionally suggested, with a dependence on bin size Δz. Direct observations confirming both the center depth of the side-lobe reflection and the depth of contamination are presented for six bottom mounted, upward-looking ADCPs. The side-lobe reflection is isolated by considering periods of weak wind stresses when the sea surface is smooth and there is nearly perfect reflection of the main beams away from the ADCP and hence little acoustic return from the main beams to the ADCP.

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Acoustic Doppler current profiler performance in near surface and bottom boundaries

Cited by 19 publications

References 2 publications

Diurnal Cycles of Near‐Surface Currents Across the Tropical Pacific

Diurnal Cycles of Near‐Surface Currents Across the Tropical Pacific

Residual circulation in western Long Island Sound

A Note on the Depth of Sidelobe Contamination in Acoustic Doppler Current Profiles

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