Evaluating the surface circulation in the Ebro delta (northeastern Spain) with quality-controlled high-frequency radar measurements

Abstract. The Ebro River delta is a relevant marine protected area in the western Mediterranean. In order to promote the conservation of its ecosystem and support operational decision making in this sensitive area, a three-site standard-range (13.5 MHz) CODAR SeaSonde high-frequency (HF) radar was deployed in December 2013. The main goal of this work is to explore basic features of the sea surface circulation in the Ebro deltaic region as derived from reliable HF radar surface current measurements. For this aim, a combined quality control methodology was applied: firstly, 1-year long (2014) real-time web monitoring of nonvelocity-based diagnostic parameters was conducted to infer both radar site status and HF radar system performance. The signal-to-noise ratio at the monopole exhibited a consistent monthly evolution, although some abrupt decreases (below 10 dB), occasionally detected in June for one of the radar sites, impacted negatively on the spatiotemporal coverage of total current vectors. It seemed to be sporadic episodes since radar site overall performance was found to be robust during 2014. Secondly, a validation of HF radar data with independent in situ observations from a moored current meter was attempted for May–October 2014. The accuracy assessment of radial and total vectors revealed a consistently high agreement. The directional accuracy of the HF radar was rated at better than 8°. The correlation coefficient and root mean square error (RMSE) values emerged in the ranges [0.58–0.83] and [4.02–18.31] cm s−1, respectively. The analysis of the monthly averaged current maps for 2014 showed that the HF radar properly represented basic oceanographic features previously reported, namely, the predominant southwestward flow, the coastal clockwise eddy confined south of the Ebro delta mouth, or the Ebro River impulsive-type freshwater discharge. The EOF analysis related the flow response to local wind forcing and confirmed that the surface current field evolved in space and time according to three significantly dominant modes of variability.

[1]  N. Levanon.  Lowest GDOP in 2-D scenarios , 2000 .

[2]  Simone Cosoli,et al.  Validation of Surface Current Measurements in the Northern Adriatic Sea from High-Frequency Radars , 2010 .

[3]  K. Taylor.  Summarizing multiple aspects of model performance in a single diagram , 2001 .

[4]  P. K. Kundu,et al.  Ekman Veering Observed near the Ocean Bottom , 1976 .

[5]  Hugh Roarty,et al.  Automated quality control of high frequency radar data II , 2012, OCEANS 2016 MTS/IEEE Monterey.

[7]  Pablo Lorente,et al.  Validation of high-frequency radar ocean surface current observations in the NW of the Iberian Peninsula , 2015 .

[8]  J. Font.  A comparison of seasonal winds with currents on the continental slope of the Catalan Sea (northwestern Mediterranean) , 1990 .

[9]  S. Cailleau,et al.  The MyOcean IBI Ocean Forecast and Reanalysis Systems: operational products and roadmap to the future Copernicus Service , 2015 .

[10]  Lucy R. Wyatt,et al.  A two year comparison between HF radar and ADCP current measurements in Liverpool Bay , 2011 .

[11]  A. Mazzoldi,et al.  A Real-Time and Offline Quality Control Methodology for SeaSonde High-Frequency Radar Currents , 2012 .

[12]  Lucy R. Wyatt.  Improving the quality control and accuracy of HF radar currents , 2015, OCEANS 2015 - Genova.

[13]  P. K. Kundu,et al.  Some Three-Dimensional Characteristics of Low-Frequency Current Fluctuations near the Oregon Coast , 1976 .

[14]  A. Sánchez-Arcilla,et al.  Influence of benthic boundary layer dynamics on wind‐induced currents in the Ebro delta inner shelf , 2002 .

[15]  Clifford R. Merz,et al.  Assessment of CODAR SeaSonde and WERA HF Radars in Mapping Surface Currents on the West Florida Shelf , 2014 .

[16]  Irina I. Rypina,et al.  Eulerian and Lagrangian Correspondence of High-Frequency Radar and Surface Drifter Data: Effects of Radar Resolution and Flow Components , 2014 .

[17]  F. Chavez,et al.  Calibration and Validation of Direction-Finding High-Frequency Radar Ocean Surface Current Observations , 2006, IEEE Journal of Oceanic Engineering.

[18]  S. Cosoli,et al.  Surface circulation in the Gulf of Trieste (northern Adriatic Sea) from radar, model, and ADCP comparisons , 2013 .

[19]  Eric Terrill,et al.  Improving SeaSonde radial velocity accuracy and variance using radial metrics , 2015, OCEANS 2015 - Genova.

[20]  Robert F. Cahalan,et al.  Sampling Errors in the Estimation of Empirical Orthogonal Functions , 1982 .

[21]  D. A. Trujillo,et al.  Accuracy of surface current velocity measurements obtained from HF radar in Corpus Christi Bay, Texas , 2004, IGARSS 2004. 2004 IEEE International Geoscience and Remote Sensing Symposium.

[22]  S. Piedracoba,et al.  Accuracy assessment of high frequency radar current measurements in the Strait of Gibraltar , 2014 .

[23]  Robert E. Synovec,et al.  Data Analysis Methods , 2012 .

[24]  Eric Terrill,et al.  Skill Assessment of Resolving Ocean Surface Current Structure Using Compact-Antenna-Style HF Radar and the MUSIC Direction-Finding Algorithm , 2007 .

[25]  Scott Glenn,et al.  Improving HF Radar Surface Current Measurements with Measured Antenna Beam Patterns , 2003 .

[26]  Libe Washburn,et al.  Evaluating Radial Current Measurements from CODAR High-Frequency Radars with Moored Current Meters , 2004 .

[27]  George O. Marmorino,et al.  Empirical Orthogonal Function Analysis of Ocean Surface Currents Using Complex and Real-Vector Methods* , 1998 .

[28]  D. Crombie,et al.  Doppler Spectrum of Sea Echo at 13.56 Mc./s. , 1955, Nature.

[29]  Simone Cosoli,et al.  Surface current variability and wind influence in the northeastern Adriatic Sea as observed from high-frequency (HF) radar measurements , 2012 .

[30]  Alexander Barth,et al.  Assimilation of HF radar surface currents to optimize forcing in the northwestern Mediterranean Sea , 2014 .

[31]  Jordi Font,et al.  Permanent features of the circulation in the Catalan Sea , 1988 .

[32]  S. Glenn,et al.  Automated quality control of High Frequency radar data , 2012, 2012 Oceans.

[33]  R. O. Schmidt,et al.  Multiple emitter location and signal Parameter estimation , 1986 .

[34]  Hans C. Graber,et al.  On the accuracy of HF radar surface current measurements: Intercomparisons with ship‐based sensors , 1997 .

[35]  Raúl Medina,et al.  Surface water circulation patterns in the southeastern Bay of Biscay: New evidences from HF radar data , 2014 .

[36]  Hans C. Graber,et al.  HF radar comparisons with moored estimates of current speed and direction: Expected differences and implications , 1997 .

[37]  David M. Kaplan,et al.  HF radar observations of surface circulation off Bodega Bay (northern California, USA) , 2005 .

[38]  William J. Emery,et al.  Data Analysis Methods in Physical Oceanography , 1998 .

[39]  Improvements in ocean surface radar applications through real-time data quality-control , 2015, 2015 IEEE/OES Eleveth Current, Waves and Turbulence Measurement (CWTM).

[40]  D. Barrick,et al.  Correcting for distorted antenna patterns in CODAR ocean surface measurements , 1986 .

[41]  Eric Terrill,et al.  Improving HF Radar Estimates of Surface Currents Using Signal Quality Metrics, with Application to the MVCO High-Resolution Radar System , 2012 .

[42]  R. Chant,et al.  Kinematics of Inner Shelf Motions during the Summer Stratified Season off New Jersey , 2000 .

[43]  D.P. Atwater,et al.  A first approach to SeaSonde quality control , 2011, OCEANS'11 MTS/IEEE KONA.

[44]  Øyvind Breivik,et al.  A short-term predictive system for surface currents from a rapidly deployed coastal HF radar network , 2012, Ocean Dynamics.

[45]  Y. Yoshikawa,et al.  On the accuracy of HF radar measurement in the Tsushima Strait , 2006 .

[46]  Joseph Gonella,et al.  A rotary-component method for analysing meteorological and oceanographic vector time series , 1972 .

[47]  Libe Washburn,et al.  Interpretation of Coastal HF Radar–Derived Surface Currents with High-Resolution Drifter Data , 2007 .

[48]  D. Gomis,et al.  Seasonal changes of water mass structure and shelf slope exchanges at the Ebro Shelf (NW Mediterranean) , 2002 .

[49]  Joanna Staneva,et al.  Blending Surface Currents from HF Radar Observations and Numerical Modeling: Tidal Hindcasts and Forecasts , 2015 .

[50]  B. Lipa,et al.  SeaSonde Radial Velocities: Derivation and Internal Consistency , 2006, IEEE Journal of Oceanic Engineering.

[51]  S. Marinetti,et al.  HF radar observations in the northern Adriatic: surface current field in front of the Venetian Lagoon , 2004 .

[52]  Pablo Lorente,et al.  Towards the implementation of a fully operational HF coastal radar network operated by Puertos del Estado , 2015, OCEANS 2015 - Genova.

[53]  David M. Kaplan,et al.  Spatial interpolation and filtering of surface current data based on open‐boundary modal analysis , 2007 .

[54]  Hans C. Graber,et al.  VALIDATION OF HF RADAR MEASUREMENTS , 1997 .

[55]  J. Font,et al.  The seasonality of mesoscale motion in the northern current of the western mediterranean - several years of evidence , 1995 .

[56]  Clifford R. Merz,et al.  Real-time quality control of current velocity data on individual grid cells in WERA HF radar , 2014, OCEANS 2014 - TAIPEI.