Performance assessment of advanced ocean current sensors

Appell, G.

doi:10.1109/oceans.1977.1154350

Cited by 3 publications

(2 citation statements)

References 1 publication

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“…Many papers address the theory of electromagnetic flow measurement [e.g., Shercliff, 1962;Bevir, 1970]. Other studies address the behavior of these current meters from an empirical point of view, most of which is published in unreviewed literature, including extensive tests run by the NOAA National Oceanographic Instrumentation Center (e.g., Appell [1977] and much unpublished material). Cushing [1976, and earlier work] discussed theory and observations of the behavior of electromagnetic current meters.…”

Section: Introductionmentioning

confidence: 99%

Kinematic and dynamic estimates from electromagnetic current meter data

Aubrey¹,

Trowbridge²

1985

J. Geophys. Res.

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The dynamic response of electromagnetic current meters (manufactured by Marsh‐McBirney, Inc.) has been clarified through a comprehensive laboratory measurement program combined with a thorough literature review. Elucidation of the behavior of these flow meters under a variety of dynamic conditions has been neglected in the past. Since flow past a spherical body has considerable hydrodynamic complexity for different dynamic conditions, a careful laboratory study was carried out for pure steady, pure oscillatory (horizontal plane), and combined steady/oscillatory conditions at two test facilities. Test results indicate that flow meter behavior under pure steady flow is reasonable in the absence of high levels of free‐stream turbulence, with an rms error of 1–5 cm/s. These errors could be reduced with a higher‐order polynomial regression fit. Pure oscillatory response was also reasonable, with rms errors of 1–2 cm/s, and sensitivity which is correlated with the oscillatory Reynolds number (Re)0, and the Keulegan‐Carpenter number (A/d, where A is the oscillation excursion and d is the probe diameter). Combined steady/oscillatory flows degraded current meter performance with larger residual errors (1–6 cm/s) and significant differences in sensitivity (up to 20%). Horizontal cosine response showed systematic deviations from pure cosine behavior, with a notable intercardinal undersensitivity and cosine “shoulder” at lower Reynolds numbers. Error analysis shows these current sensors are adequate for many kinematic measurements but may lead to excessive errors when using velocity to calculate dynamical quantities (such as bottom friction, Reynolds stress, or log‐layer friction velocities). A careful error analysis must precede any use of these meters for estimating dynamical quantities. These studies pointed out a potential difficulty in using these meters in areas of large ambient turbulence levels (20% turbulent intensities), which are characteristic of many near‐bottom shallow water environments. Further study is needed to clarify this behavior.

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Section: Introductionmentioning

confidence: 99%

Kinematic and dynamic estimates from electromagnetic current meter data

Aubrey¹,

Trowbridge²

1985

J. Geophys. Res.

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“…McBirney [1975] describes good vertical cosine response for this probe via graphs of measurements made at a single unspecified current magnitude. Jones et al [1978], Jones and Bruzzone [1981], Kalvaitis [ 1977], and Appell [ 1979] demonstrate that vertical cosine response is dependent on the geometry of the instrument housing but that excellent response is attainable. Appell [ 1979], Kalvaitis [ 1977], and McCullough [ 1979] summarize the vertical velocity-induced errors for this probe as well as other sensors as a function of mean to fluctuating current ratios.…”

Section: Current Sensormentioning

confidence: 99%

An upper ocean moored current and density profiler applied to winter conditions near Bermuda

Eriksen¹,

Dahlen²,

Shillingford³

1982

J. Geophys. Res.

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A new moored instrument which makes repeated high vertical resolution profiles of current, temperature, and salinity in the upper ocean over extended periods was used to observe midwinter conditions near Bermuda. The operation and performance of the instrument, called the profiling current meter (PCM), in the surface wave environment of winter storms is reported here. The PCM profiles along the upper portion of a slightly subsurface mooring by adjusting its buoyancy under computer control. This design decouples the instrument from vertical motions of the mooring induced by surface waves, so that its electromagnetic current sensor operates in a favorable mean‐to‐fluctuating flow regime. Current, temperature, and electrical conductivity are (vector) averaged into contiguous preselected bins several meters wide over the possible profile range of 20‐ to 250‐m depth. The PCM is capable of collecting 1000–4000 profiles in a 6‐ to 12‐month period, depending on depth range and ambient currents. A variety of baroclinic motions are evident in the Bermuda observations. Upper ocean manifestations of both Kelvin and superinertial island‐trapped waves dominate longshore currents. Vertical coherences of onshore current and temperature suggest that internal wave vertical wave number energy distribution is independent of frequency but modified by island bathymetry. Kinetic energy in shear integrated over a 115.6‐m‐thick layer in the upper ocean is limited to values less than or equal to the potential energy required to mix the existing stratification. Mixing events occur when kinetic energy associated with shear drives the bulk Richardson number (defined by the ratio of energy integrals over the range profiled) to unity, where it remains while shear and stratification disappear together.

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