Fluctuation of High-Turbidity Water Measured by Acoustic Doppler Current Profiler at the Izena Calderon in the Okinawa Trough

2011 ◽  
Author(s):  
Rei Arai ◽  
Yusuke Onobayashi ◽  
Hiroshi Ishida ◽  
Nobuhiro Maeda ◽  
Tomoya Sugimoto ◽  
...  
Keyword(s):  
Okinawa Trough ◽  
Acoustic Doppler Current Profiler ◽  
Massive Sulfide ◽  
Tectonic Activity ◽  
Time Frequency ◽  
The Okinawa Trough ◽  
Current Profiler ◽  
Adcp Measurements ◽  
High Turbidity ◽  
Hydrothermal Environment

Hydrothermal processes associated with spreading centers of plate-tectonic activity form seafloor massive sulfide (SMS) deposits. Given that the SMS deposits found in the western Pacific have been considered to be potential sources of gold (Au), silver (Ag), cupper (Cu), zinc (Zn), and lead (Pb) including manganese nodules and cobalt-rich manganese crusts, there is a strong possibility that they will be mined in near future. In order to take measures against environmental impact during the mining of SMS deposits, it is important to measure components of hydrothermal origin with high temporal and spatial resolution on site, and to understand the ecosystem in the hydrothermal environment. In this study, we first propose a measurement method of turbidity profiles using an Acoustic Doppler Current Profiler (ADCP). Applying this method to the ADCP measurements in the Izena Calderon with SMS in the Okinawa Trough, we verify that this method can extract turbidity data from echo intensities measured by ADCP. Subsequently, we describe the high-turbidity water in the Izena Calderon measured by ADCP, and present and discuss the turbidity fluctuations estimated by applying time-frequency analysis to these turbidity data.

scholarly journals A Method for Processing Acoustic Doppler Current Profiler Velocity Data from Towed, Undulating Vehicles

2008 ◽  
Vol 25 (9) ◽  
pp. 1710-1716 ◽  
Author(s):  
Jiayi Pan ◽  
David A. Jay
Keyword(s):  
Surface Waters ◽  
High Frequency ◽  
Acoustic Doppler Current Profiler ◽  
Small Time ◽  
Ocean Current ◽  
Near Surface ◽  
Vertical Range ◽  
External Reference ◽  
Current Profiler ◽  
Adcp Measurements

Abstract The utility of the acoustic Doppler current profiler (ADCP) for sampling small time and space scales of coastal environments can be enhanced by mounting a high-frequency (1200 kHz) ADCP on an oscillating towed body. This approach requires both an external reference to convert the measured shears to velocities in the earth coordinates and a method to determine the towed body velocities. During the River Influence on the Shelf Ecosystems (RISE) project cruise, a high-frequency (1200 kHz) and narrowbeam ADCP with mode 12 sampling was mounted on a TRIAXUS oscillating towfish, which steers a 3D path behind the ship. This deployment approach extended the vertical range of the ADCP and allowed it to sample near-surface waters outside the ship’s wake. The measurements from a ship-mounted 1200-kHz narrowbeam ADCP are used as references for TRIAXUS ADCP data, and a method of overlapping bins is employed to recover the entire vertical range of the TRIAXUS ADCP. The TRIAXUS vehicle horizontal velocities are obtained by removing the derived ocean current velocity from the TRIAXUS ADCP measurements. The results show that the method is practical.

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 Temporal variations of zooplankton biomass in the Ligurian Sea inferred from long time series of ADCP data

Ocean Science ◽  
2014 ◽  
Vol 10 (1) ◽  
pp. 93-105 ◽  
Author(s):  
R. Bozzano ◽  
E. Fanelli ◽  
S. Pensieri ◽  
P. Picco ◽  
M. E. Schiano
Keyword(s):  
Time Series ◽  
Acoustic Doppler Current Profiler ◽  
Temporal Variations ◽  
Zooplankton Biomass ◽  
Mesopelagic Fish ◽  
Ligurian Sea ◽  
Time Frequency ◽  
Backscattering Strength ◽  
Current Profiler ◽  
Long Time

Abstract. Three years of 300 kHz acoustic doppler current profiler data collected in the central Ligurian Sea are analysed to investigate the variability of the zooplankton biomass and the diel vertical migration in the upper thermocline. After a pre-processing phase aimed at avoiding the slant range attenuation, hourly volume backscattering strength time series are obtained. Despite the lack of concurrent net samples collection, different migration patterns are identified and their temporal variability examined by means of time–frequency analysis. The effect of changes in the environmental condition is also investigated. The highest zooplankton biomasses are observed in April–May just after the peak of surface primary production in March–April. The main migration pattern found here points to a "nocturnal" migration, with zooplankton organisms occurring deeper in the water column during the day and shallower at night. Also, twilight migration is highlighted during this study. The largest migrations are recorded in November–December, corresponding to lowest backscattering strength values and they are likely attributable to larger and more active organisms (i.e. euphausiids and mesopelagic fish). The results suggest further applications of the available historical acoustic doppler current profiler time series.

scholarly journals Global Wavenumber Spectrum with Corrections for Altimeter High-Frequency Noise

2015 ◽  
Vol 45 (2) ◽  
pp. 495-503 ◽  
Author(s):  
Xiao-Hui Zhou ◽  
Dong-Ping Wang ◽  
Dake Chen
Keyword(s):  
High Frequency ◽  
Acoustic Doppler Current Profiler ◽  
High Energy ◽  
Frequency Noise ◽  
Spectral Estimates ◽  
Current Profiler ◽  
Adcp Measurements ◽  
Corrected Data ◽  
Geostrophic Turbulence ◽  
The Tropics

AbstractThe altimetry wavenumber spectra of sea surface height (SSH) provide a unique dataset for testing of geostrophic turbulence. While SSH spectral slopes of k−11/3 and k−5 are expected from theories and numerical simulations, the altimetry spectra from the original unfiltered and instrument noise–corrected data often are too shallow, falling between k−2 and k−3. In this study, the possibility that the flattened spectral slopes are partly due to contamination by unresolved high-frequency (<10 days) motions is tested. A spatiotemporal filter based on empirical orthogonal function expansion (EOF) is used to remove the temporally incoherent signals. The resulting spectral slopes are much steeper than in the previous studies. Over 70% of the revised global spectral estimates, excluding the tropics, are above k−3. Moreover, in high energy regions like the Gulf Stream and Kuroshio, the spectral slopes are about k−5, which is consistent with the classical quasigeostrophic (QG) turbulence. The spectral slopes are validated with the eddy kinetic energy (EKE) spectra from shipboard acoustic Doppler current profiler (ADCP) measurements in the high and low energy regions.

scholarly journals PARTICLE SIZE CHARACTERISTICS OF RIVERBED SEDIMENTS TRANSPORTED BY TIDAL BORE ‘BONO’ IN KAMPAR ESTUARY, RIAU-INDONESIA

2018 ◽  
Vol 43 (1) ◽  
pp. 25-35
Author(s):  
Wisnu Arya Gemilang ◽  
Ulung Jantama Wisha ◽  
Guntur Adhi Rahmawan
Keyword(s):  
Mass Transfer ◽  
Grain Size ◽  
Acoustic Doppler Current Profiler ◽  
Tidal Bore ◽  
Riverbed Sediments ◽  
Sediment Mass ◽  
Current Profiler ◽  
Adcp Measurements ◽  
Tidal Condition ◽  
Size Data

The presence of tidal bore in the Kampar River (locally known as ‘bono’) may influence sedimentation in the Kampar River and its estuary. Understanding sedimentation mechanisms (e.g., erosion, deposition) is important to communities along the Kampar River, which can be studied by analyzing characteristics of grain size distribution. Here, we study riverbed sediment samples collected from 17 stations using an Ekman grab sampler, accompanied by bathymetry and acoustic Doppler current profiler (ADCP) measurements. Grain size data show that the sediments are coarser upstream and gradually finer downstream. Silty sands are predominant in the upstream section of the river, sands in its river body and sandy silts in the downstream. The results indicate the influence of undular bores on grain size characteristics. We also found that the propagation of bono and Kampar River’s funnelshaped morphology cause intense scouring events of riverbed sediments. Sortation values that range between 0.332.14 suggest unstable currents that result in randomly deposited sediments. The sediment mass transfer per area is positively towards downstream at the low tidal condition. However, after the passage of the bores, the sediment mass transfer area becomes negatively towards upstream.

Characteristics of the Environment Around a Massive Sea-Floor Sulfide Area in the Okinawa Trough

2011 ◽  
Author(s):  
Hiroshi Ishida ◽  
Nobuhiro Maeda ◽  
Tetsuya Miwa ◽  
Tetsuo Yamazaki ◽  
Yoshihisa Shirayama ◽  
...  
Keyword(s):  
Hydrothermal Vent ◽  
Okinawa Trough ◽  
Euphotic Zone ◽  
Bottom Layer ◽  
Massive Sulfide ◽  
Baseline Survey ◽  
Surrounding Area ◽  
Sea Floor ◽  
The Okinawa Trough ◽  
Ca 50

It is necessary to carry out a proper environmental impact assessment for not only the sea-floor massive sulfide area where a special hydrothermal-vent chemosynthetic ecosystem is observed, but also its surrounding area. This paper shows provisional results of the environmental baseline survey conducted at the Izena Cauldron in 2009. Environmental conditions differed clearly between inside and outside of the Cauldron. In the inside area, a high turbidity layer was recognized at ca. 200 m above the sea-floor. In the bottom layer close to the hydrothermal active region, water temperature was slightly higher than the surrounding area with the lower pH, higher concentrations of both carbon dioxide and the dissolved Mn. Inside the Cauldron, the sulfur isotope ratio of the sediment close to a sea-floor massive sulfide was similar to that of the hydrothermal sulfate. In addition, heavy metal concentrations of the sediment were higher inside than outside of the Cauldron. Especially, concentrations of Cd, As and Hg were as high as poisonous levels. These results show the possibility that most of the chemical materials derived from hydrothermal vent remain in the Cauldron. Pelagic shrimps of the family Oplophoridae were widely distributed in the bottom layer inside the Cauldron. The biomass of benthic shrimps which belong to infraorder Caridea was higher inside than outside of the Cauldron. These higher biomass was likely caused by the abundant organic matter. This hypothesis was reinforced by the result of the mooring sediment trap (placed at ca. 50 m above the seafloor) experiment, which demonstrated that the settling particle in the Cauldron was supplied from not only the euphotic zone but also the hydrothermal-vent ecosystem.

Acoustic Doppler Current Profiler (ADCP) Measurements of Breaking Waves

2008 ◽  
Author(s):  
Anne M. Fullerton ◽  
Thomas C. Fu
Keyword(s):  
Acoustic Doppler Current Profiler ◽  
Breaking Waves ◽  
Primary Objective ◽  
Breaking Wave ◽  
Flow Measurements ◽  
Measurement Systems ◽  
Bubble Density ◽  
Current Profiler ◽  
Adcp Measurements ◽  
Naval Surface Warfare

Detailed flow measurements of the turbulent multiphase flow associated with wave breaking present a unique instrumentation challenge. Measurement systems must be capable of high sampling rates, large dynamic ranges, and be capable of making measurements in water, air and optically opaque regions. An experiment was performed at the Naval Surface Warfare Center, Carderock Division, in October 2007 to measure various characteristics of the breaking wave generated from a submerged ship transom. The primary objective of this work was to obtain full-scale qualitative and quantitative flow field data of a large breaking transom wave over a range of conditions, specifically transom drafts and Froude numbers. Several types of measurements were made on the transom stern wave during this experiment, however, this paper will focus on the Nortek Acoustic Wave and Current (AWAC) profiler measurements of the stern wake. The AWAC has a center acoustic beam in addition to the three angled beams typically found on an acoustic Doppler current profiler. The trends of the acoustic return from the AWAC and the trends of the bubble density and location on the water surface compare well, and it is anticipated that this return can be related to void fraction and bubble measurements in the future. This type of non-intrusive measurement could be very useful in the evaluation of breaking waves.

scholarly journals Observing Directional Properties of Ocean Swell with an Acoustic Doppler Current Profiler (ADCP)

2010 ◽  
Vol 27 (1) ◽  
pp. 210-225 ◽  
Author(s):  
T. H. C. Herbers ◽  
S. J. Lentz
Keyword(s):  
Continental Shelf ◽  
Acoustic Doppler Current Profiler ◽  
Parametric Estimation ◽  
Monitoring Applications ◽  
Current Profiler ◽  
Adcp Measurements ◽  
Directional Wave ◽  
Acoustic Doppler Current Profilers ◽  
Good Agreement

Abstract Acoustic Doppler current profilers (ADCPs) are widely used for routine measurements of ocean currents and waves in coastal environments. These instruments have the basic capability to measure surface wave frequency–directional spectra, but the quality of the estimates is not well understood because of the relatively high noise levels in the velocity measurements. In this study, wave data are evaluated from two 600-kHz ADCP instruments deployed at 20- and 45-m depths on the Southern California continental shelf. A simple parametric estimation technique is presented that provides robust estimates of the gross directional wave properties, even when the data quality is marginal, as was often the case in this benign wave environment. Good agreement of mean direction and (to a lesser degree) directional spreading estimates with measurements from a nearby surface-following buoy confirms that reliable wave information can generally be extracted from ADCP measurements on the continental shelf, supporting the instrument’s suitability for routine wave-monitoring applications.

Extracting Reynolds Stresses from Acoustic Doppler Current Profiler Measurements in Wave-Dominated Environments

2008 ◽  
Vol 25 (2) ◽  
pp. 286-306 ◽  
Author(s):  
Johanna H. Rosman ◽  
James L. Hench ◽  
Jeffrey R. Koseff ◽  
Stephen G. Monismith
Keyword(s):  
Reynolds Stress ◽  
Simple Procedure ◽  
Acoustic Doppler Current Profiler ◽  
French Polynesia ◽  
Reynolds Stresses ◽  
Variance Method ◽  
Beam Velocity ◽  
Current Profiler ◽  
Adcp Measurements ◽  
Velocity Variances

Abstract Surface waves introduce velocity correlations that bias and often dominate Reynolds stress estimates made using the traditional variance method for acoustic Doppler current profilers (ADCPs). This analysis shows that the wave bias is the sum of a real wave stress and an error due to instrument tilt, both of which have a large uncertainty. Three alternative extensions to the variance method for calculating Reynolds stress profiles from ADCP measurements in wavy conditions are analyzed. The previously proposed variance fitting method (Variance Fit) is evaluated and two more general methods that use along- and between-beam velocity differencing with adaptive filtering (Vertical AF and Horizontal AF) are derived. The three methods are tested on datasets containing long-period monochromatic swell (Moorea, French Polynesia) and shorter-period mixed swell (Santa Barbara, California). The Variance Fit method leaves a residual wave bias in beam velocity variances, especially for intermediate waves, but gives physically reasonable Reynolds stress estimates because most of the residual wave bias cancels when the variance method is applied. The new Vertical AF method does not produce inherent wave bias in beam velocity variances, but yields comparable Reynolds stresses to the Variance Fit method. The Horizontal AF method performs poorly for all but monochromatic waves. Error remaining after one of the above methods is applied can be attributed to residual wave error, correlation of turbulence between points chosen for differencing, or correlation between waves and turbulence. A simple procedure is provided for determining the minimum bin separation that can be used.

scholarly journals Wavenumber Spectrum in the Gulf Stream from Shipboard ADCP Observations and Comparison with Altimetry Measurements

2010 ◽  
Vol 40 (4) ◽  
pp. 840-844 ◽  
Author(s):  
Dong-Ping Wang ◽  
Charles N. Flagg ◽  
Kathleen Donohue ◽  
H. Thomas Rossby
Keyword(s):  
Gulf Stream ◽  
Acoustic Doppler Current Profiler ◽  
Sea Surface ◽  
Turbulence Theory ◽  
Velocity Spectrum ◽  
Height Measurement ◽  
Measured Velocity ◽  
Current Profiler ◽  
Adcp Measurements ◽  
Geostrophic Turbulence

Abstract The wavenumber spectra for velocity and temperature in the Gulf Stream region are calculated from a decade (1994–2004) of shipboard acoustic Doppler current profiler (ADCP) measurements taken as part of the Oleander Project. The velocity and temperature spectra have comparable magnitude, in terms of the kinetic and potential energy, and both indicate a k−3 slope in the mesoscales. In contrast, the corresponding velocity spectrum determined from satellite altimetry sea surface heights yields a significantly higher energy level and a k−2 slope. The discrepancy between altimeter-derived and directly measured velocity spectra suggests that altimetric velocity probably is contaminated by noise in sea surface height measurement. Also, the k−3 slope, which appears to be in agreement with two-dimensional quasigeostrophic turbulence theory, does not support the contemporary surface quasigeostrophic theory. These results highlight large gaps in the current understanding of the nature of surface geostrophic turbulence.

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