scholarly journals Eddy Detection in HF Radar-Derived Surface Currents in the Gulf of Naples

2019 ◽  
Vol 12 (1) ◽  
pp. 97 ◽  
Author(s):  
Leonardo Bagaglini ◽  
Pierpaolo Falco ◽  
Enrico Zambianchi
Keyword(s):  
Velocity Fields ◽  
Automated Detection ◽  
Hf Radar ◽  
Surface Currents ◽  
Tracer Transport ◽  
Gulf Of Naples ◽  
Radar Systems ◽  
Inorganic Matter ◽  
Radar Velocity ◽  
Synoptic Observations

Submesoscale eddies play an important role in the energy transfer from the mesoscale down to the dissipative range, as well as in tracer transport. They carry inorganic matter, nutrients and biomass; in addition, they may act as pollutant conveyors. However, synoptic observations of these features need high resolution sampling, in both time and space, making their identification challenging. Therefore, HF coastal radar were and are successfully used to accurately identify, track and describe them. In this paper we tested two already existing algorithms for the automated detection of submesoscale eddies. We applied these algorithms to HF radar velocity fields measured by a network of three radar systems operating in the Gulf of Naples. Both methods showed shortcomings, due to the high non-geostrophy of the observed currents. For this reason we developed a third, novel algorithm that proved to be able to detect highly asymmetrical eddies, often not properly identified by the previous ones. We used the results of the application of this algorithm to estimate the eddy boundary profiles and the eddy spatial distribution.

scholarly journals Measurement Characteristics of Near-Surface Currents from Ultra-Thin Drifters, Drogued Drifters, and HF Radar

2018 ◽  
Vol 10 (10) ◽  
pp. 1633 ◽  
Author(s):  
Steven Morey ◽  
Nicolas Wienders ◽  
Dmitry Dukhovskoy ◽  
Mark Bourassa
Keyword(s):  
High Frequency ◽  
Measurement Techniques ◽  
Hf Radar ◽  
Stokes Drift ◽  
Surface Velocity ◽  
Surface Currents ◽  
Material Transport ◽  
Surface Shear ◽  
Near Surface ◽  
Radar Velocity

Concurrent measurements by satellite tracked drifters of different hull and drogue configurations and coastal high-frequency radar reveal substantial differences in estimates of the near-surface velocity. These measurements are important for understanding and predicting material transport on the ocean surface as well as the vertical structure of the near-surface currents. These near-surface current observations were obtained during a field experiment in the northern Gulf of Mexico intended to test a new ultra-thin drifter design. During the experiment, thirty small cylindrical drifters with 5 cm height, twenty-eight similar drifters with 10 cm hull height, and fourteen drifters with 91 cm tall drogues centered at 100 cm depth were deployed within the footprint of coastal High-Frequency (HF) radar. Comparison of collocated velocity measurements reveals systematic differences in surface velocity estimates obtained from the different measurement techniques, as well as provides information on properties of the drifter behavior and near-surface shear. Results show that the HF radar velocity estimates had magnitudes significantly lower than the 5 cm and 10 cm drifter velocity of approximately 45% and 35%, respectively. The HF radar velocity magnitudes were similar to the drogued drifter velocity. Analysis of wave directional spectra measurements reveals that surface Stokes drift accounts for much of the velocity difference between the drogued drifters and the thin surface drifters except during times of wave breaking.

scholarly journals Improved Detection of the First-Order Region for Direction-Finding HF Radars Using Image Processing Techniques

2017 ◽  
Vol 34 (8) ◽  
pp. 1679-1691 ◽  
Author(s):  
Anthony Kirincich
Keyword(s):  
Image Processing ◽  
Direction Finding ◽  
Hf Radar ◽  
Image Processing Technique ◽  
Spectral Energy ◽  
Surface Currents ◽  
Surface Gravity Wave ◽  
First Order ◽  
Radar Systems ◽  
Wave Conditions

AbstractFor direction-finding high-frequency (HF) radar systems, the correct separation of backscattered spectral energy due to Bragg resonant waves from that due to more complex double-scattering represents a critical first step toward attaining accurate estimates of surface currents from the range-dependent radar backscatter. Existing methods to identify this “first order” region of the spectra, generally sufficient for lower-frequency radars and low-velocity or low-surface gravity wave conditions, are more likely to fail in higher-frequency systems or locations with more variable current, wave, or noise regimes, leading to elevated velocity errors. An alternative methodology is presented that uses a single and globally relevant smoothing length scale, careful pretreatment of the spectra, and marker-controlled watershed segmentation, an image processing technique, to separate areas of spectral energy due to surface currents from areas of spectral energy due to more complex scattering by the wave field or background noise present. Applied to a number of HF radar datasets with a range of operating frequencies and characteristic issues, the new methodology attains a higher percentage of successful first-order identification, particularly during complex current and wave conditions. As operational radar systems continue to expand to more systematically cover areas of high marine traffic, close approaches to ports and harbors, or offshore energy installations, use of this type of updated methodology will become increasingly important to attain accurate current estimates that serve both research and operational interests.

scholarly journals Assessment of CODAR SeaSonde and WERA HF Radars in Mapping Surface Currents on the West Florida Shelf*

2014 ◽  
Vol 31 (6) ◽  
pp. 1363-1382 ◽  
Author(s):  
Yonggang Liu ◽  
Robert H. Weisberg ◽  
Clifford R. Merz
Keyword(s):  
Radial Velocity ◽  
Long Range ◽  
Hf Radar ◽  
Integration Time ◽  
Surface Currents ◽  
West Florida Shelf ◽  
The West ◽  
Florida Shelf ◽  
Radar Systems ◽  
Effective Depth

Abstract Concurrently operated on the West Florida shelf for the purpose of observing surface currents are three long-range (4.9 MHz) Coastal Ocean Dynamics Applications Radar (CODAR) SeaSonde and two median-range (12.7 MHz) Wellen Radar (WERA) high-frequency (HF) radar systems. These HF radars overlook an array of moored acoustic Doppler current profilers (ADCPs), three of which are presently within the radar footprint. Analyzed herein are 3 months of simultaneous observations. Both the SeaSonde and WERA systems generally agree with the ADCPs to within root-mean-square differences (rmsd) for hourly radial velocity components of 5.1–9.2 and 3.8–6.5 cm s−1 for SeaSonde and WERA, respectively, and within rmsd for 36-h low-pass filtered radial velocity components of 2.8–6.0 and 2.2–4.3 cm s−1 for SeaSonde and WERA, respectively. The bearing offset and tidal and subtidal currents of total velocities are also assessed using the ADCP data. Despite differences in a variety of aspects between the direction-finding CODAR SeaSonde (long range, effective depth of 2.4 m, integration time of 4 h, and idealized antenna patterns) and the beam-forming WERA (median range, effective depth of 0.9 m, and integration time of 1 h), both HF radar systems demonstrated good surface current mapping capability. The differences between the velocities measured with the HF radar and the ADCP are sufficiently small in this low-energy shelf that much of these rmsd values may be accounted for by the expected measurement differences due to the horizontal, vertical, and temporal sampling differences of the ocean current observing systems used.

Backtracking drifting objects using surface currents from high-frequency (HF) radar technology

2012 ◽  
Vol 62 (7) ◽  
pp. 1073-1089 ◽  
Author(s):  
Ana Julia Abascal ◽  
Sonia Castanedo ◽  
Vicente Fernández ◽  
Raúl Medina
Keyword(s):  
High Frequency ◽  
Hf Radar ◽  
Surface Currents

scholarly journals Assimilation of HF radar surface currents to optimize forcing in the northwestern Mediterranean Sea

2014 ◽  
Vol 21 (3) ◽  
pp. 659-675 ◽  
Author(s):  
J. Marmain ◽  
A. Molcard ◽  
P. Forget ◽  
A. Barth ◽  
Y. Ourmières
Keyword(s):  
Surface Wind ◽  
Circulation Model ◽  
Radar Data ◽  
Hf Radar ◽  
Open Boundary ◽  
Coastal Current ◽  
Surface Currents ◽  
Data Set ◽  
Radar Measurements ◽  
Northwestern Mediterranean

Abstract. HF radar measurements are used to optimize surface wind forcing and baroclinic open boundary condition forcing in order to constrain model coastal surface currents. This method is applied to a northwestern Mediterranean (NWM) regional primitive equation model configuration. A new radar data set, provided by two radars deployed in the Toulon area (France), is used. To our knowledge, this is the first time that radar measurements of the NWM Sea are assimilated into a circulation model. Special attention has been paid to the improvement of the model coastal current in terms of speed and position. The data assimilation method uses an ensemble Kalman smoother to optimize forcing in order to improve the model trajectory. Twin experiments are initially performed to evaluate the method skills. Real measurements are then fed into the circulation model and significant improvements to the modeled surface currents, when compared to observations, are obtained.

scholarly journals Comparison of HF radar measurements with Eulerian and Lagrangian surface currents

2015 ◽  
Vol 65 (5) ◽  
pp. 679-690 ◽  
Author(s):  
Johannes Röhrs ◽  
Ann Kristin Sperrevik ◽  
Kai Håkon Christensen ◽  
Göran Broström ◽  
Øyvind Breivik
Keyword(s):  
Hf Radar ◽  
Surface Currents ◽  
Lagrangian Surface ◽  
Radar Measurements
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