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.

scholarly journals Quantifying Suspended Sediment using Acoustic Doppler Current Profiler in Tidung Island Seawaters

2021 ◽  
Vol 29 (1) ◽  
Author(s):  
Henry Munandar Manik ◽  
Randi Firdaus
Keyword(s):  
Water Column ◽  
Suspended Sediment ◽  
Suspended Solids ◽  
Acoustic Doppler Current Profiler ◽  
Sediment Concentration ◽  
In Situ Measurement ◽  
Ocean Current ◽  
Echo Intensity ◽  
Current Profiler

Tidung Island, located near Jakarta Bay, is a tourism and conservation area. It is necessary to keep these seawaters unpolluted. To calculate the level of pollution, it is necessary to know the sediment concentration. Quantifying concentration suspended sediment is important for knowledge of sediment transport. Researchers usually use water sample analysis and optical method for quantifying suspended sediment in seawater. Less accuracies of these methods are due to under sample of seawater and the existence of biological fouling. One promising method to measure concentration of suspended sediment is using Acoustic Doppler Current Profiler (ADCP). ADCP is usually used by oceanographer and hydrographer to measure ocean current. In this research, ADCP with 300 kHz operating frequency was used effectively to measure suspended sediment concentration (SSC) and ocean current simultaneously. The echo intensity received from suspended sediment was computed using sonar equations to quantify SSC. The empirical equation between echo intensity and SSC was found. The SSC value obtained by ADCP was also compared with in situ measurement. The result showed that quantified SSC value obtained by ADCP was nearly equal with SSC obtained from in situ measurement with coefficient correlation of 0.98. The high concentration ranged from 55 mg/L to 80 mg/L at the surface layer to a depth 12 m, moderate concentration ranged from 45 mg/L to 55 mg/L at a depth 12 m to 40 m, and low concentration less than 45 mg/L at a depth greater than 40 m. The distribution of SSC was correlated with ocean current condition. In small currents, suspended solids will settle faster so that the concentration in the water column will decrease. Conversely, if the velocity is high, suspended solids will continue to float carried by the current in the water column so that the concentration is high.

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

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.

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.

scholarly journals Divergence-Free Spatial Velocity Flow Field Interpolator for Improving Measurements from ADCP-Equipped Small Unmanned Underwater Vehicles

2012 ◽  
Vol 29 (3) ◽  
pp. 478-484 ◽  
Author(s):  
Jamie MacMahan ◽  
Ross Vennell ◽  
Rick Beatson ◽  
Jenna Brown ◽  
Ad Reniers
Keyword(s):  
Flow Field ◽  
Signal To Noise Ratio ◽  
Acoustic Doppler Current Profiler ◽  
Unmanned Underwater Vehicles ◽  
Velocity Magnitude ◽  
Velocity Flow ◽  
Current Profiler ◽  
Adcp Measurements ◽  
Measured Flow ◽  
Divergence Free

Abstract Applying a two-dimensional (2D) divergence-free (DF) interpolation to a one-person deployable unmanned underwater vehicle’s (UUV) noisy moving-vessel acoustic Doppler current profiler (MV-ADCP) measurements improves the results and increases the utility of the UUV in tidal environments. For a 3.5-h MV-ACDP simulation that spatially and temporally varies with the M2 tide, the 2D DF-estimated velocity magnitude and orientation improves by approximately 85%. Next the 2D DF method was applied to velocity data obtained from two UUVs that repeatedly performed seven 1-h survey tracks in Bear Cut Inlet, Miami, Florida. The DF method provides a more realistic and consistent representation of the ADCP measured flow field, improving magnitude and orientation estimates by approximately 25%. The improvement increases for lower flow velocities, when the ADCP measurements have low environmental signal-to-noise ratio. However, near slack tide when flow reversal occurs, the DF estimates are invalid because the flows are not steady state within the survey circuit.

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

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.

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.

scholarly journals Prediction and classification of suspended sediment and zooplankton signals from acoustic Doppler current profiler backscatter data using artificial neural networks

2021 ◽  
Vol 944 (1) ◽  
pp. 012014
Author(s):  
A Dwinovantyo ◽  
S Solikin ◽  
H M Manik ◽  
T Prartono ◽  
Susilohadi
Keyword(s):  
Suspended Sediment ◽  
Suspended Sediment Concentration ◽  
Acoustic Doppler Current Profiler ◽  
Suspended Sediments ◽  
Sediment Concentration ◽  
Optimal Number ◽  
Environmental Data ◽  
Zooplankton Abundance ◽  
Current Profiler ◽  
Artificial Neural

Abstract Characterization of each underwater object has its challenges, especially for small objects. The process of quantifying acoustic signals for these small objects can be done using high-frequency hydroacoustic instruments such as an acoustic Doppler current profiler (ADCP) combined with the artificial intelligence (AI) technique. This paper presents an artificial neural network (ANN) methodology for classifying an object from acoustic and environmental data in the water column. In particular, the methodology was tuned for the recognition of suspended sediments and zooplankton. Suspended sediment concentration and zooplankton abundance, which extracted from ADCP acoustic data, were used as input in the backpropagation method along with other environmental data such as effects of tides, currents, and vertical velocity. The classifier used an optimal number of neurons in the hidden layer and a feature selection based on a genetic algorithm. The ANN method was also used to estimate the suspended sediment concentration in the future. This study provided new implications for predicting and classifying suspended sediment and zooplankton using the ADCP instrument. The proposed methodology allowed us to identify the objects with an accuracy of more than 95%.

scholarly journals Generation of Internal Waves by Eddies Impinging on the Western Boundary of the North Atlantic

2016 ◽  
Vol 46 (4) ◽  
pp. 1067-1079 ◽  
Author(s):  
L. Clément ◽  
E. Frajka-Williams ◽  
K. L. Sheen ◽  
J. A. Brearley ◽  
A. C. Naveira Garabato
Keyword(s):  
Internal Waves ◽  
North Atlantic ◽  
High Frequency ◽  
Large Scale ◽  
Acoustic Doppler Current Profiler ◽  
Relative Vorticity ◽  
Western Boundary ◽  
The North ◽  
Current Profiler ◽  
The North Atlantic

AbstractDespite the major role played by mesoscale eddies in redistributing the energy of the large-scale circulation, our understanding of their dissipation is still incomplete. This study investigates the generation of internal waves by decaying eddies in the North Atlantic western boundary. The eddy presence and decay are measured from the altimetric surface relative vorticity associated with an array of full-depth current meters extending ~100 km offshore at 26.5°N. In addition, internal waves are analyzed over a topographic rise from 2-yr high-frequency measurements of an acoustic Doppler current profiler (ADCP), which is located 13 km offshore in 600-m deep water. Despite an apparent polarity independence of the eddy decay observed from altimetric data, the flow in the deepest 100 m is enhanced for anticyclones (25.2 cm s−1) compared with cyclones (−4.7 cm s−1). Accordingly, the internal wave field is sensitive to this polarity-dependent deep velocity. This is apparent from the eddy-modulated enhanced dissipation rate, which is obtained from a finescale parameterization and exceeds 10−9 W kg−1 for near-bottom flows greater than 8 cm s−1. The present study underlines the importance of oceanic western boundaries for removing the energy of low-mode westward-propagating eddies to higher-mode internal waves.

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