Current velocity measurements using acoustic Doppler backscatter: A review

Woodward, William E.; Appell, G.

doi:10.1109/joe.1986.1145147

Cited by 23 publications

(3 citation statements)

References 13 publications

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“…Africana. The development and general procedures of current measurement by means of acoustic Doppler techniques are covered in Woodward and Appell (1986) and RD Instruments (1986). Details of the RDI hardware and software are given by RD Instruments (1988.…”

Section: Data Sources and Methodsmentioning

confidence: 99%

Spatial features of the near-surface and midwater circulation patterns off western and southern South Africa and their role in the life histories of various commercially fished species

Boyd¹,

Taunton-Clark²,

Oberholster³

1992

South African Journal of Marine Science

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Currents on the South African shelf have been measured on 13 cruises since an Acoustic Doppler Current Profiler (ADCP) was installed on F.R.S. Africana in ]989. Most previous descriptions of the West Coast (Benguela) system, including the baroclinic jet currents off the Cape Peninsula and Cape Columbine, the ]aller clearly diverging into a dominant offshore arm and a weaker inshore arm, have been confirmed. This baroclinic flow originates along the south-western margin of the Agulhas Bank. Measurements of the inshore features of the Agulhas Current have shown strong WSW -SSW flow aligned with the bathymetry, but with significant she]fedge north-eastward return flows. The velocity differences between the surface and depth reveal barotropic dominance in all inshore areas and over the central Agulhas Bank. The West Coast outer shelf displays variable baroclinic effects, reflecting the importance of frontal features and cross-shelf flow. SSW flow on the outer eastern Agulhas Bank appears responsible for an offshore loss of eggs from this region. The funnelling of anchovy eggs from the western Agulhas Bank to the West Coast was clear, but this "funnel" was found to have holes through which substantial loss of eggs offshore is also probable. The currents on the Agulhas Bank and the West Coast are discussed with regard to the life histories of various commercially fished species, in addition to anchovy. The study concludes that hypotheses relating environmental factors and recruitment need to consider the variety of potential options in terms of life history contained within the prevailing current system. Seder! 'n Doppler-Akoestiese Stroomprofileerder in 1989 op VNS. Africana aangebring is, is strome tydens 13 vaarte op die Suid-Afrikaanse vastelandsplat gemeel. Die meeste vorige beskrywings van die Weskus (Benguela)stelsel is bevestig, met inbegrip van die barokliniese snelstrome teenoor die Kaapse Skiereiland en Kaap Columbine en laasgenoemde se ooglopende vertakking in 'n oorheersende aflandige been en 'n swakker aanlandige been. Hierdie barokliniese vloei het sy oorsprong langs die suidwestelike grens van die Agulhasbank. Metings van die aanlandige kenmerke van die Agulhasstroom het sterk WSW tot SSW vloei vertoon in ooreenstemming met die batimetrie, maar met beduidende noordoostelike terugkeervloei aan die rand van die vastelandsplal. Verskille in vloeisnelheid tussen die oppervlak en dieper water dui op barotropiese oorheersing in aile aanlandige gebiede en oor die sentrale Agulhasbank. Die afIandige streek van die plat aan die Weskus word gekenmerk deur wisselvallige barokliniese gevolge wat die belang van frontale kenmerke en dwarsvloei oor die plat beklemtoon. SSW vloei op die buitenste oostelike Agulhasbank is blykbaar verantwoordelik vir seewaartse verlies van eiers uit hierdie streek. Daar is onteenseglik 'n tregtereffek op beweging van ansjoviseiers van die weste]ike Bank na die Weskus, maar die "tregter" het openinge waardeur ook aansienlike seewaartse eierverlies waarskynlik is. Vermelde strome op die A...

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Section: Data Sources and Methodsmentioning

confidence: 99%

Spatial features of the near-surface and midwater circulation patterns off western and southern South Africa and their role in the life histories of various commercially fished species

Boyd¹,

Taunton-Clark²,

Oberholster³

1992

South African Journal of Marine Science

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“…One potential means of examining behaviour within swarms is through acoustic Doppler current profilers (ADCPs), which measure Doppler shift in particles, principally as a means of measuring water velocity and direction. The instrument makes its calculations based on the assumption that all ensonified particles move passively [14], but this assumption may be violated if particles within any ensonifed layers are dominated by directionally swimming organisms. For instance, Wilson & Firing [15] found that residuals from tidal fits to ADCP data were conspicuously large at sunrise, which they considered to be a bias from coherent horizontal swimming of dominant acoustic targets.…”

Section: Introductionmentioning

confidence: 99%

Oceanic swarms of Antarctic krill perform satiation sinking

Tarling

Thorpe

2017

Proc. R. Soc. B.

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Antarctic krill form some of the highest concentrations of animal biomass observed in the world's oceans potentially due to their prolific ability to swarm. Determining the movement of Antarctic krill within swarms is important to identify drivers of their behaviour and their biogeochemical impact on their environment. We examined vertical velocity within approximately 2000 krill swarms through the combined use of a shipborne echosounder and an acoustic Doppler current profiler. We revealed a pronounced downward anomaly in vertical velocity within swarms of -0.6 cm s compared with vertical motion outside the swarm. The anomaly changed over the diel cycle, with smaller downward anomalies occurring at night. Swarms in regions of high phytoplankton concentrations (a proxy for food availability) also exhibited significantly smaller downward anomalies. We propose that the anomaly is the result of downward velocities generated by the action of krill beating their swimming appendages. During the night and in high phytoplankton availability, when krill are more likely to feed to the point of satiation, swimming activity is lowered and the anomaly is reduced. Our findings are consistent with laboratory work where krill ceased swimming and adopted a parachute posture when sated. Satiation sinking behaviour can substantially increase the efficiency of carbon transport to depth through depositing faecal pellets at the bottom of swarms, avoiding the reingestion and break-up of pellets by other swarm members.

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“…For shipboard systems, an array of three-five downwardslanting acoustic beams, each measuring the along-axis component of velocity versus range, is used to estimate the ocean velocity field (Pinkel 1980;Regier 1982;Woodward and Appell 1986). Consider the return from a single beam of mean elevation f with respect to the vertical and one-sided beamwidth Df.…”

Section: Introductionmentioning

confidence: 99%

Velocity Imprecision in Finite-Beamwidth Shipboard Doppler Sonar: A First-Generation Correction Algorithm

Pinkel

2012

Journal of Atmospheric and Oceanic Technology

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The finite angular width of Doppler sonar beams introduces errors into the measurement of ocean velocity from moving ships. These errors are exacerbated as ship speed increases and as the acoustic scatter field becomes more inhomogeneous in space. Zooplanktonic scatters often reside in distinct quasi-isopycnal scattering layers. When measured from a moving ship, such layers appear to have a distinct velocity signature, even if the ocean is quiescent. Here, this effect is explored in a simple analytic model and a least squares algorithm is presented for remediating its signature. The algorithm corrects the measured velocity at any given depth, with the correction being a weighted sum of the depth gradient of log acoustic intensity at surrounding depths. The correction weights are a property of the specific sonar beam pattern. Once determined, they can be considered constant. The algorithm, when applied to a 50-kHz sonar on the Research Vessel (R/V) Roger Revelle, is found to remove roughly 90% of the error in vertical wavenumber spectra of shear. More sophisticated algorithms can be developed as experience with the present approach is gained.

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Current velocity measurements using acoustic Doppler backscatter: A review

Cited by 23 publications

References 13 publications

Spatial features of the near-surface and midwater circulation patterns off western and southern South Africa and their role in the life histories of various commercially fished species

Spatial features of the near-surface and midwater circulation patterns off western and southern South Africa and their role in the life histories of various commercially fished species

Oceanic swarms of Antarctic krill perform satiation sinking

Velocity Imprecision in Finite-Beamwidth Shipboard Doppler Sonar: A First-Generation Correction Algorithm

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