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Bias in mean velocities and noise in variances and covariances measured using a multistatic acoustic profiler: the Nortek Vectrino Profiler

Creelle, S.; Thomas, R E; Schindfessel, L; McLelland, S J; Creëlle, S; De Mulder, T

Authors

Dr Robert Thomas R.E.Thomas@hull.ac.uk
Senior Research Fellow in Geomorphology and Flood Risk

S. Creelle

Abstract

This paper compiles the technical characteristics and operating principles of the Nortek Vectrino Profiler and reviews previously reported user experiences. A series of experiments are then presented that investigate instrument behaviour and performance, with a particular focus on variations within the profile. First, controlled tests investigate the sensitivity of acoustic amplitude (and Signal-to-Noise Ratio, SNR) and pulse-to-pulse correlation coefficient, R 2 , to seeding concentration and cell geometry. Second, a novel methodology that systematically shifts profiling cells through a single absolute vertical position investigates the sensitivity of mean velocities, SNR and noise to: (a) emitted sound intensity and the presence (or absence) of acoustic seeding; and (b) varying flow rates under ideal acoustic seeding conditions. A new solution is derived to quantify the noise affecting the two perpendicular tristatic systems of the Vectrino Profiler and its contribution to components of the Reynolds stress tensor. Results suggest that for the Vectrino Profiler: 1. optimum acoustic seeding concentrations are ∼3000 to 6000 mg L -1 ; 2. mean velocity magnitudes are biased by variable amounts in proximal cells but are consistently underestimated in distal cells; 3. noise varies parabolically with a minimum around the 'sweet spot', 50 mm below the transceiver; 4. the receiver beams only intersect at the sweet spot and diverge nearer to and further from the transceiver. This divergence significantly reduces the size of the sampled area away from the sweet spot, reducing data quality; 5. the most reliable velocity data will normally be collected in the region between approximately 43 and 61 mm below the transceiver.

Journal Article Type Article
Publication Date Jul 1, 2017
Journal Measurement science and technology
Print ISSN 0957-0233
Electronic ISSN 1361-6501
Publisher IOP Publishing
Peer Reviewed Peer Reviewed
Volume 28
Issue 7
Pages 075302
DOI https://doi.org/10.1088/1361-6501/aa7273
Keywords Vectrino Profiler, Bias, Noise, Measurement error, Velocity measurement, Acoustic Doppler velocimetry, Sensitivity
Publisher URL http://iopscience.iop.org/article/10.1088/1361-6501/aa7273
Copyright Statement © 2017 IOP Publishing Ltd, this Accepted Manuscript is available for reuse under a CC BY-NC-ND 3.0 licence.
Additional Information Journal title: Measurement Science and Technology; Article type: paper; Article title: Bias in mean velocities and noise in variances and covariances measured using a multistatic acoustic profiler: the Nortek Vectrino Profiler; Copyright information: © 2017 IOP Publishing Ltd; Date received: 2016-12-16; Date accepted: 2017-05-11; Online publication date: 2017-06-19

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