scholarly journals Current Patterns in the Inner Sound (Pentland Firth) from Underway ADCP Data*

2013 ◽  
Vol 30 (1) ◽  
pp. 96-111 ◽  
Author(s):  
Lonneke Goddijn-Murphy ◽  
David K. Woolf ◽  
Matthew C. Easton
Keyword(s):  
Acoustic Doppler Current Profiler ◽  
Tidal Energy ◽  
Current Data ◽  
Northern Coast ◽  
Orkney Islands ◽  
The North ◽  
Tidal Changes ◽  
Current Profiler ◽  
Tidal Stream ◽  
Tidal Streams

AbstractNumerous acoustic Doppler current profiler (ADCP) surveys were performed in the Inner Sound of the Pentland Firth, a channel between the Orkney Islands and the northern coast of Scotland connecting the Atlantic Ocean to the west and the North Sea to the east. The Pentland Firth has the highest tidal streams of the British Isles, and one of the highest that can be found around the globe. Here, the tidal energy industry is in its demonstration phase, but not many real current measurements are in the public domain. The authors present real current data, measured during different phases of the tidal cycle, using a vessel-mounted ADCP. The tidal changes can be rapid, and because the underway measurements take time, the apparent spatial patterns are affected by temporal variation. A method is described that estimated and corrected this temporal distortion using a hydrodynamic model. It appeared that ebb and flood streams did not fully overlap, and that the tidal streams were more complicated, turbulent, and variable than existing models suggest. The data were analyzed for characteristics pertinent to practical tidal stream energy exploitation, and two favorable sites in the Inner Sound are identified. All original current data are available from the British Oceanographic Data Centre (BODC).

scholarly journals A stable Faroe Bank Channel overflow 1995–2015

2016 ◽  
Author(s):  
Bogi Hansen ◽  
Karin Margretha Húsgarð Larsen ◽  
Hjálmar Hátún ◽  
Svein Østerhus
Keyword(s):  
Acoustic Doppler Current Profiler ◽  
Narrow Channel ◽  
Volume Transport ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Positive Trend ◽  
The North ◽  
Denmark Strait ◽  
Current Profiler ◽  
Meridional Overturning

Abstract. The Faroe Bank Channel is the deepest passage across the Greenland-Scotland Ridge (GSR), and through it, there is a continuous deep flow of cold and dense water passing from the Arctic Mediterranean into the North Atlantic and further to the rest of the World oceans. This FBC-overflow is part of the Atlantic Meridional Overturning Circulation (AMOC), which has recently been suggested to have weakened. From November 1995 to May 2015, the FBC-overflow has been monitored by a continuous ADCP (Acoustic Doppler Current Profiler) mooring, which has been deployed in the middle of this narrow channel. Combined with regular hydrography cruises and several short-term mooring experiments, this allows us to construct time series of volume transport and to follow changes in the hydrographic properties and density of the FBC-overflow. The mean kinematic overflow, derived from the velocity field solely, was found to be (2.2 ± 0.2) Sv (1 Sv = 106 m3 s−1) with a slight, but not statistically significant, positive trend. The coldest part, and probably the bulk, of the FBC-overflow warmed by a bit more than 0.1 °C, especially after 2002. This warming was, however, accompanied by increasing salinities, which seem to have compensated for the temperature-induced density decrease. Thus, the FBC-overflow has remained stable in volume transport as well as density during the two decades from 1995 to 2015. This is consistent with reported observations from the other main overflow branch, the Denmark Strait overflow, and the three Atlantic inflow branches to the Arctic Mediterranean that feed the overflows. If the AMOC has weakened during the last two decades, it is not likely to have been due to its northernmost extension – the exchanges across the Greenland-Scotland Ridge.

Stratifikasi Massa Air di Teluk Lasolo, Sulawesi Tenggara

2016 ◽  
Vol 1 (2) ◽  
pp. 17
Author(s):  
Dewi Surinati ◽  
Edi Kusmanto
Keyword(s):  
North Pacific ◽  
Water Mass ◽  
Acoustic Doppler Current Profiler ◽  
Current Data ◽  
Water Masses ◽  
Intermediate Water ◽  
North Pacific Intermediate Water ◽  
Conservation Area ◽  
Current Profiler ◽  
Salinity Data

<strong>Stratification of Water Mass in Lasolo Bay, Southeast Sulawesi.</strong> As a nature conservation area, Lasolo Bay should be supported by data and information of waters oceanographic. Research for stratification of water masses in Lasolo Bay was conducted. from 10 to 19 July 2011. Temperature and salinity data were obtained using CTD SBE 911 Plus preinstalled on Research Vessel Baruna Jaya VIII at intervals of 24 data per second. Current data were obtained using Vessel Mounted Acoustic Doppler Current Profiler (VMADCP) with an interval of two seconds. The results show that there are differences in the speed and direction of currents in the water column that lead to stratification of water masses. Currents that drove the water mass of Banda Sea into Lasolo Bay was caused by southeasterly winds with an average speed of 4.1 m/s. At depths of 0–50 m and 100–200 m the current dominance occurs to the northwest, while at depths of 50–100 m and 200–350 m it occurs to the south. The water mass with a salinity of 32.1–34.0 PSU and temperature 26–28°C occupied the surface layer (0–50 m). The water mass with a salinity of 34.4–34.5 PSU identified as the water mass of North Pacific Intermediate Water (NPIW) occupied two depths, i.e. 50–100 m and 200–350 m with different range of temperatures. The water mass with maximum salinity (34.5–34.6 PSU), identified as the water mass of North Pacific Subtropical Water (NPSW) also occupied two depths i.e. 100–200 m and 350 m until near the bottom with different range of temperatures<br /><br />

scholarly journals Analysis of tidal currents in the North Sea from shipboard acoustic Doppler current profiler data

2018 ◽  
Vol 162 ◽  
pp. 1-12 ◽  
Author(s):  
Håvard Vindenes ◽  
Kjell Arild Orvik ◽  
Henrik Søiland ◽  
Henning Wehde
Keyword(s):  
North Sea ◽  
Acoustic Doppler Current Profiler ◽  
Tidal Currents ◽  
The North ◽  
Current Profiler ◽  
The North Sea ◽  
Profiler Data

scholarly journals Bardsey – an island in a strong tidal stream: underestimating coastal tides due to unresolved topography

Ocean Science ◽  
2020 ◽  
Vol 16 (6) ◽  
pp. 1337-1345
Author(s):  
J. A. Mattias Green ◽  
David T. Pugh
Keyword(s):  
Satellite Altimetry ◽  
Energy Resource ◽  
Tidal Energy ◽  
Small Scale ◽  
Phase Lag ◽  
Wake Effect ◽  
Tidal Dissipation ◽  
Tidal Energetics ◽  
Tidal Stream ◽  
Tidal Streams

Abstract. Bardsey Island is located at the western end of the Llŷn Peninsula in northwestern Wales. Separated from the mainland by a channel that is some 3 km wide, it is surrounded by reversing tidal streams of up to 4 m s−1 during spring tides. These local hydrodynamic details and their consequences are unresolved by satellite altimetry and are not represented in regional tidal models. Here we look at the effects of the island on the strong tidal stream in terms of the budgets for tidal energy dissipation and the formation and shedding of eddies. We show, using local observations and a satellite-altimetry-constrained product (TPXO9), that the island has a large impact on the tidal stream and that even in this latest altimetry-constrained product the derived tidal stream is under-represented due to the island not being resolved. The effect of the island leads to an underestimate of the current speed in the TPXO9 data in the channel of up to a factor of 2.5, depending on the timing in the spring–neap cycle, and the average tidal energy resource is underestimated by a factor up to 14. The observed tidal amplitudes are higher at the mainland than at the island, and there is a detectable phase lag in the tide across the island; this effect is not seen in the TPXO9 data. The underestimate of the tide in the TPXO9 data has consequences for tidal dissipation and wake effect computation and shows that local observations are key to correctly estimating tidal energetics around small-scale coastal topography.

scholarly journals A stable Faroe Bank Channel overflow 1995–2015

Ocean Science ◽  
2016 ◽  
Vol 12 (6) ◽  
pp. 1205-1220 ◽  
Author(s):  
Bogi Hansen ◽  
Karin Margretha Húsgarð Larsen ◽  
Hjálmar Hátún ◽  
Svein Østerhus
Keyword(s):  
World Ocean ◽  
Deep Ocean ◽  
Acoustic Doppler Current Profiler ◽  
Narrow Channel ◽  
Volume Transport ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Positive Trend ◽  
The North ◽  
Current Profiler

Abstract. The Faroe Bank Channel (FBC) is the deepest passage across the Greenland–Scotland Ridge (GSR) and there is a continuous deep flow of cold and dense water passing through it from the Arctic Mediterranean into the North Atlantic and further to the rest of the world ocean. This FBC overflow is part of the Atlantic Meridional Overturning Circulation (AMOC), which has recently been suggested to have weakened. From November 1995 to May 2015, the FBC overflow has been monitored by a continuous ADCP (acoustic Doppler current profiler) mooring, which has been deployed in the middle of this narrow channel. Combined with regular hydrography cruises and several short-term mooring experiments, this allowed us to construct time series of volume transport and to follow changes in the hydrographic properties and density of the FBC overflow. The mean kinematic overflow, derived solely from the velocity field, was found to be (2.2 ± 0.2) Sv (1 Sv  =  106 m3 s−1) with a slight, but not statistically significant, positive trend. The coldest part, and probably the bulk, of the FBC overflow warmed by a bit more than 0.1 °C, especially after 2002, increasing the transport of heat into the deep ocean. This warming was, however, accompanied by increasing salinities, which seem to have compensated for the temperature-induced density decrease. Thus, the FBC overflow has remained stable in volume transport as well as density during the 2 decades from 1995 to 2015. After crossing the GSR, the overflow is modified by mixing and entrainment, but the associated change in volume (and heat) transport is still not well known. Whatever effect this has on the AMOC and the global energy balance, our observed stability of the FBC overflow is consistent with reported observations from the other main overflow branch, the Denmark Strait overflow, and the three Atlantic inflow branches to the Arctic Mediterranean that feed the overflows. If the AMOC has weakened during the last 2 decades, it is not likely to have been due to its northernmost extension – the exchanges across the Greenland–Scotland Ridge.

scholarly journals On the Reliability of Surface Current Measurements by X-band Marine Radar

2019 ◽  
Vol 11 (9) ◽  
pp. 1030 ◽  
Author(s):  
Hessner ◽  
El Naggar ◽  
von Appen ◽  
Strass
Keyword(s):  
Real Time ◽  
Surface Current ◽  
Acoustic Doppler Current Profiler ◽  
Weather Conditions ◽  
Operational Reliability ◽  
Current Data ◽  
X Band ◽  
Current Profiler ◽  
Marine Radar ◽  
Commercial Off The Shelf

Real-time quality-controlled surface current data derived from X-Band marine radar (MR) measurements were evaluated to estimate their operational reliability. The presented data were acquired by the standard commercial off-the-shelf MR-based sigma s6 WaMoS® II (WaMoS® II) deployed onboard the German Research vessel Polarstern. The measurement reliability is specified by an IQ value obtained by the WaMoS® II real-time quality control (rtQC). Data which pass the rtQC without objection are assumed to be reliable. For these data sets accuracy and correlation with corresponding vessel-mounted acoustic Doppler current profiler (ADCP) measurements are determined. To reduce potential misinterpretation due to short-term oceanic variability/turbulences, the evaluation of the WaMoS® II accuracy was carried out based on sliding means over 20 min of the reliable data only. The associated standard deviation σWaMoS = 0.02 m/s of the mean WaMoS® II measurements reflect a high precision of the measurement and the successful rtQC during different wave, current and weather conditions. The direct comparison of 7272 WaMoS® II/ADCP northward and eastward velocity data pairs yield a correlation of r ≥0.94, with bias∆ ≤0.06 m/s and σS=0.05 m/s. This confirms that the MR-based surface current measurements are accurate and reliable.

Extracting Meaningful Information from Uncalibrated Backscattered Echo Intensity Data

2010 ◽  
Vol 27 (5) ◽  
pp. 943-949 ◽  
Author(s):  
Louis Gostiaux ◽  
Hans van Haren
Keyword(s):  
Transmission Loss ◽  
Signal To Noise Ratio ◽  
Acoustic Doppler Current Profiler ◽  
Sediment Concentration ◽  
Original Method ◽  
Air Bubbles ◽  
Echo Intensity ◽  
The North ◽  
Current Profiler ◽  
The North Sea

Abstract The authors present an original method for the analysis of acoustic Doppler current profiler (ADCP) echo intensity profiles measured in the ocean, especially when no calibration has been performed. This study is based on data from Teledyne RD Instrument acoustic profilers but provides a methodology that can be extended to other kinds of hardware. To correctly interpret data for which the signal-to-noise ratio is below a factor of 10, the authors propose isolating the backscattered signal from noise in arithmetic space before resolving the sonar equation and compensating for transmission loss in logarithmic space. The robustness of the method is shown for several independent datasets from the Atlantic Ocean, the North Sea, and the Mediterranean Sea. Estimation of sediment concentration, planktonic migrations, or air bubbles is now possible at less than 10 dB above noise level, which can concern half of the ADCP’s range under common circumstances.

Dynamics of tidal mixing fronts in the North Sea

1993 ◽  
Vol 343 (1669) ◽  
pp. 431-446 ◽  
Keyword(s):  
North Sea ◽  
Baroclinic Instability ◽  
Acoustic Doppler Current Profiler ◽  
Hf Radar ◽  
Tidal Mixing ◽  
The North ◽  
Current Profiler ◽  
Shelf Sea ◽  
The North Sea ◽  
New Generation

Twenty years since the discovery of tidal mixing fronts there are still few convincing observations of the velocity field associated with these structures. Simple models of shelf sea fronts predict strong along-front jets, weaker convergent circulations and instabilities. During the North Sea Project a series of studies of the Flamborough frontal system has used a new approach based upon novel combinations of modern instrumentation (HF radar, acoustic Doppler current profiler, Decca-Argos drifting buoys and towed undulating CTD) and have provided one of the first directly observed pictures of shelf sea frontal circulation. Observational confirmation of jetlike along-front flow has been found together with evidence of cross-frontal convergence. A new generation of eddy-resolving models will help to focus the next phase of frontal circulation studies in relation to questions concerning baroclinic instability and eddy generation.

Observations of Nepheloid Layers in the Yangtze Estuary, China, Through Phase-Corrupted Acoustic Doppler Current Profiler Speeds

2012 ◽  
Vol 46 (4) ◽  
pp. 60-70 ◽  
Author(s):  
Zhenyi Cao ◽  
Xiao Hua Wang ◽  
Weibing Guan ◽  
Les J. Hamilton ◽  
Qi Chen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Acoustic Doppler Current Profiler ◽  
Yangtze Estuary ◽  
Fluid Mud ◽  
Nepheloid Layer ◽  
The Yangtze Estuary ◽  
Mean Velocity ◽  
The North ◽  
Navigation Channel ◽  
Current Profiler

AbstractA bottom quadrapod was deployed from March 29 to April 5, 2009 to measure bottom boundary layer (BBL) flows and nepheloid layer properties in the Deepwater Navigation Channel in the North Passage of Shanghai Port in the Yangtze estuary. Using a downward-looking acoustic Doppler current profiler (ADCP) and acoustic Doppler velocimeter, detailed measurements of mean velocity and turbulence distribution within 1 m above the seabed were obtained. It appears that corrupted speeds measured for the deeper bins are caused by formation of the nepheloid layer at the seabed, implying that the ADCP is not a suitable instrument to measure current velocities in the bins nearest the seafloor. A statistical clustering method was used to characterize the current profiles in the BBL. The majority of current profiles within the BBL had a simple shape with current speed monotonically decreasing with depth, reflecting a logarithmic boundary layer. Phase-corrupted ADCP speeds measured for bins close to the bottom are shown to be useful as proxies to indicate the presence of primary and secondary lutoclines/nepheloid layers. A lutocline is a sediment-induced density gradient or pycnocline. The primary lutocline is closest to the bottom, and below it is the nepheloid layer, which is commonly composed of fluid mud. The proxies indicated that a nepheloid layer formed in the neap tide when the current velocity 1 m above the seabed dropped below a threshold of 0.65 m/s. The lutocline height was indicated to be about 0.2 m above the seabed. A secondary lutocline in the water column was also observed in the second half of the record, when the lowest maximum currents occurred.

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