The Leeuwin Current near Rottnest Island, Western Australia

1996 ◽  
Vol 47 (3) ◽  
pp. 483 ◽  
Author(s):  
G Cresswell
Keyword(s):  
Satellite Image ◽  
Acoustic Doppler Current Profiler ◽  
Maximum Speed ◽  
Temperature Structure ◽  
Near Surface ◽  
Fish Schools ◽  
Leeuwin Current ◽  
Low Salinity ◽  
Current Profiler ◽  
Good Agreement

Ship data and a satellite image in June 1987 showed the Leeuwin Current as a warm, low-salinity tropical stream travelling southward inshore of the 180-m isobath with near-surface speeds up to 0.9 m s-1. Farther offshore, where the waters became progressively more subtropical, the southward currents were also quite strong--0.75 m s-1 above the continental slope and over 0.4 m s-1 out to 70 km beyond the shelf edge. Beyond this, a doming of 150 m in the temperature structure at several hundred metres depth drove a cyclonic eddy that had its maximum speed of ~0.5 m s-1 in a ring at 200-400 m depth. The presence of the eddy was confirmed by the path of a drifter. Geostrophic currents and currents measured directly with an Acoustic Doppler Current Profiler showed good agreement. The warm 'shoulder' of the Leeuwin Current between the 105-m and 135-m isobaths was a biological oasis characterized by, inter alia, several fish schools at least 10 km long and 1 km wide and with vertical extents from 20 m to more than 100 m depth.

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 A NEW STRATEGIC WAVE MEASUREMENT STATION OFF NAPLES PORT MAIN BREAKWATER

2017 ◽  
pp. 36 ◽  
Author(s):  
Luca Centurioni ◽  
Lance Braasch ◽  
Enrico Di Lauro ◽  
Pasquale Contestabile ◽  
Francesco De Leo ◽  
...  
Keyword(s):  
Wave Energy ◽  
Low Cost ◽  
Acoustic Doppler Current Profiler ◽  
Wave Spectra ◽  
Sea State ◽  
Gulf Of Naples ◽  
Current Profiler ◽  
Directional Wave ◽  
Low Costs ◽  
Good Agreement

The accuracy of directional wave spectra sensors is crucial for obtaining accurate forecasts of ocean and coastal wave conditions for scientific and engineering applications. In this paper, a newly designed, low-cost GPS-based wave buoy, called the Directional Wave Spectra Drifter (DWSD), is presented. A field test campaign was conducted at the Gulf of Naples, Italy with the goal of comparing the directional wave properties obtained with the DWSD and with a nearly co-located bottom-mounted Acoustic Doppler Current Profiler (ADCP) from Teledyne RD-Instruments. The comparison shows a very good agreement between the two methodologies. The reliability of this innovative instrument and its low costs allow a large variety of applications, including the implementation of a global, satellite-linked, real-time open-ocean network of drifting directional wave spectra sensors and monitoring the sea-state in harbors to aid ship transit and for planning coastal and offshore constructions. The DWSD is currently in use to better constrain the wave energy climatology with the goal of optimizing the design of a full-scale prototype Wave Energy Converter (WEC) in the port of Naples, Italy.

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.

scholarly journals Tracking icebergs with time-lapse photography and sparse optical flow, LeConte Bay, Alaska, 2016–2017

2019 ◽  
Vol 65 (250) ◽  
pp. 195-211 ◽  
Author(s):  
CHRISTIAN KIENHOLZ ◽  
JASON M. AMUNDSON ◽  
ROMAN J. MOTYKA ◽  
REBECCA H. JACKSON ◽  
JOHN B. MICKETT ◽  
...  
Keyword(s):  
Optical Flow ◽  
Acoustic Doppler Current Profiler ◽  
Time Lapse ◽  
Image Resolution ◽  
Secondary Importance ◽  
Near Surface ◽  
Spatial Image ◽  
Flow Speeds ◽  
Current Profiler ◽  
Lower Frame

ABSTRACTWe present a workflow to track icebergs in proglacial fjords using oblique time-lapse photos and the Lucas-Kanade optical flow algorithm. We employ the workflow at LeConte Bay, Alaska, where we ran five time-lapse cameras between April 2016 and September 2017, capturing more than 400 000 photos at frame rates of 0.5–4.0 min−1. Hourly to daily average velocity fields in map coordinates illustrate dynamic currents in the bay, with dominant downfjord velocities (exceeding 0.5 m s−1 intermittently) and several eddies. Comparisons with simultaneous Acoustic Doppler Current Profiler (ADCP) measurements yield best agreement for the uppermost ADCP levels (~ 12 m and above), in line with prevalent small icebergs that trace near-surface currents. Tracking results from multiple cameras compare favorably, although cameras with lower frame rates (0.5 min−1) tend to underestimate high flow speeds. Tests to determine requisite temporal and spatial image resolution confirm the importance of high image frame rates, while spatial resolution is of secondary importance. Application of our procedure to other fjords will be successful if iceberg concentrations are high enough and if the camera frame rates are sufficiently rapid (at least 1 min−1 for conditions similar to LeConte Bay).

scholarly journals Interoperability of SeaSondes and Wellen Radars in Mapping Radial Surface Currents

2013 ◽  
Vol 30 (11) ◽  
pp. 2662-2675 ◽  
Author(s):  
J. Martinez-Pedraja ◽  
L. K. Shay ◽  
B. K. Haus ◽  
C. Whelan
Keyword(s):  
Acoustic Doppler Current Profiler ◽  
Hf Radar ◽  
Small Scale ◽  
Surface Currents ◽  
Florida Current ◽  
Current Profiler ◽  
Florida Straits ◽  
Subsurface Current ◽  
Geometric Dilution Of Precision ◽  
Good Agreement

Abstract A dual-station high-frequency (HF) Wellen Radar (WERA) transmitting at 16 MHz has observed near-real-time surface currents over an approximate range of 100 km across the Florida Straits since July 2004. During a 10-day period in April 2005 (15–25 April), a pair of 12.6-MHz SeaSondes (SS) were deployed south of the WERAs sites by NOAA's Center for Operational Oceanographic Products and Services (CO-OPS). The resulting SS grid overlapped the southern portion of the WERA domain. During the same period of time, a bottom-mounted acoustic Doppler current profiler (ADCP) acquired subsurface current measurements within these HF radar grids starting at 14 m below the surface in water of 86-m depth. The interoperability of beam-forming (WERA) and direction-finding (SS) HF radar technologies was examined. Comparisons of radial and vector currents for an 8-day concurrent time series suggested good agreement in current direction over both domains, where the surface currents' magnitudes were a maximum of 1.2 m s−1. In the core of the radar domains consisting of 108 cells, hourly vector currents were obtained by combining WERA and SS radials. Generally, this can be done in a relatively straightforward manner, considering the geometric dilution of precision (GDOP). A second key issue is downscaling the SS measurements from a 3-km grid to a 1.1-km grid to match the WERA output. This enhanced grid spacing is important along the western flank of the Florida Current, where energetic, small-scale surface features have been observed.

Characteristics of ice in the St. Lawrence River

2003 ◽  
Vol 30 (4) ◽  
pp. 766-774 ◽  
Author(s):  
Brian Morse ◽  
Masoud Hessami ◽  
Céline Bourel
Keyword(s):  
Fuzzy Logic ◽  
Wind Velocity ◽  
Air Temperature ◽  
Acoustic Doppler Current Profiler ◽  
Navigation Channel ◽  
Current Profiler ◽  
Adcp Data ◽  
St Lawrence River ◽  
Good Agreement

The main objective of this paper is to describe the characteristics of brash ice in the St. Lawrence River downstream of Montréal over a period of three winters. We used two instruments deployed in the St. Lawrence River navigation channel through Lake St. Pierre to measure ice parameters: an acoustic Doppler current profiler (ADCP) and an ice-profiling sonar (IPS). This paper discusses the capacities of these instruments to quantify ice characteristics and to predict the risk of ice congestion. It was found that wind velocity and air temperature play major roles in the variation in ice parameters and, consequently, in the occurrence of ice congestion in the navigation channel through Lake St. Pierre. Comparison of the IPS and ADCP data showed good agreement and demonstrated that these two instruments can be very effective for certain ice applications.Key words: ice characteristics, ice congestion, ADCP, IPS, fuzzy logic.

scholarly journals The Leeuwin Current south of Western Australia

1993 ◽  
Vol 44 (2) ◽  
pp. 285 ◽  
Author(s):  
GR Cresswell ◽  
JL Peterson
Keyword(s):  
Wind Stress ◽  
Western Australia ◽  
Satellite Image ◽  
Subtropical Water ◽  
Tropical Waters ◽  
Leeuwin Current ◽  
Low Salinity ◽  
Tropical Water ◽  
Autumn And Winter

Satellite images as well as data collected in situ were used to follow the seasonal changes of the Leeuwin Current south of Western Australia (WA) in 1986-87. The current has two major sources: salty subtropical water from west of WA, and fresher tropical water from north of WA. In summer, the tropical waters are excluded by the strong equatorward wind stress. In autumn and winter, this wind stress is reduced and tropical waters flood southward to dominate the flow. Nevertheless, salty subtropical water is entrained en route, and so, whatever the season, the Leeuwin Current is more saline than the 'local' subantarctic waters off southern WA. From a research vessel, observations were made on the current and one of its offshoots in June 1987. The Leeuwin Current had a maximum surface speed of more than 1 m s-1 just beyond the shelf edge. Its warm, low-salinity surface core rode on a sheath of higher-salinity subtropical water that it had entrained upstream. The first survey of the offshoot showed it to be 50 km across and 130 m deep (for water warmer than 17�C), and it extended 200 km seaward (as deduced from a satellite image). Velocities in the offshoot ranged up to 1 m s-1 southward and 1 m s-1 north-eastward on the western and eastern sides, respectively. Richardson numbers were, in places, as low as 0.25. On a second survey two days later, the offshoot was found to have pinched off and the remnant bulge on the edge of the parent stream to have moved 30 km eastward. The flow around this bulge reached 1.6 m s-'. The offshoot/bulge was possibly first formed in April, and it kept its identity at least until August. During this time, it moved eastward at speeds between 2 and 15 km day-1. In June, the offshoot was estimated to contain water equivalent to five days' transport of the parent current.

scholarly journals Near-Surface Ocean Kinetic Energy Spectra and Small-Scale Intermittency from Ship-Based ADCP Data in the Bay of Bengal

2020 ◽  
Vol 50 (7) ◽  
pp. 2037-2052
Author(s):  
Jai Sukhatme ◽  
Dipanjan Chaudhuri ◽  
Jennifer MacKinnon ◽  
S. Shivaprasad ◽  
Debasis Sengupta
Keyword(s):  
Kinetic Energy ◽  
Bay Of Bengal ◽  
Wave Spectrum ◽  
Acoustic Doppler Current Profiler ◽  
Surface Flow ◽  
Small Scale ◽  
Stratified Turbulence ◽  
Near Surface ◽  
Current Profiler ◽  
Along Track

AbstractHorizontal currents in the Bay of Bengal were measured on eight cruises covering a total of 8600 km using a 300-kHz acoustic Doppler current profiler (ADCP). The cruises are distributed over multiple seasons and regions of the Bay. Horizontal wavenumber spectra of these currents over depths of 12–54 m and wavelengths from 2 to 400 km were decomposed into rotational and divergent components assuming isotropy. An average of across- and along-track spectra over all cruises shows that the spectral slope of horizontal kinetic energy for wavelengths of 10–80-km scales with an exponent of −1.7 ± 0.05, which transitions to a steeper slope for wavelengths above 80 km. The rotational component is significantly larger than the divergent component at scales greater than 80 km, while the ratio of the two is nearly constant with a mean of 1.16 ± 0.4 between 10 and 80 km. The measurements show a fair amount of variability and spectral levels vary between cruises by about a factor of 5 over 10–100 km. Velocity differences over 10–80 km show probability density functions and structure functions with stretched exponential behavior and anomalous scaling. Comparisons with the Garrett–Munk internal wave spectrum indicate that inertia–gravity waves account for only a modest fraction of the kinetic energy between 10 and 80 km. These constraints suggest that the near-surface flow in the Bay is primarily balanced and follows a forward enstrophy transfer quasigeostrophic regime for wavelengths greater than approximately 80 km, with a larger role for unbalanced rotating stratified turbulence and internal waves at smaller scales.

scholarly journals Thermal structure and circulation in Lake Chapala, Mexico

2016 ◽  
Vol 75 (s1) ◽  
Author(s):  
David Avalos-Cueva ◽  
Anatoliy Filonov ◽  
Iryna Tereshchenko ◽  
César O. Monzón ◽  
Federico Á. Velázquez-Muñoz
Keyword(s):  
Thermal Structure ◽  
Acoustic Doppler Current Profiler ◽  
Dry Season ◽  
Spatial Average ◽  
Average Temperature ◽  
Lake Chapala ◽  
Anticyclonic Gyre ◽  
Current Profiler ◽  
Adcp Measurements ◽  
Good Agreement

<p>This study analyzed and discussed the instrumental measurements of temperature and currents made on January 10, 2007, in Lake Chapala. We received new data on the formation of the thermocline. It is shown that the thermocline of the lake is formed only in the daytime and in a top-heated 0.5-1.0 m layer. The vertical temperature gradient reaches 2.5°C in the first meter, and the spatial average temperature across the lake showed that the northern end of the lake is, on average, 1°C warmer than the southern end. We numerically modelled the currents in the lake for the dry season using the HAMSOM 2D hydrodynamic model. The simulation results are in good agreement with the acoustic Doppler current profiler ADCP measurements. In the dry season, two gyres were found: a cyclonic gyre in the eastern part and an anticyclonic gyre in the western part.</p>

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