HF Radar observations of the Dardanelles outflow current in North Eastern Aegean using validated WERA HF radar data

Abstract

A two-site WERA High Frequency radar (HF radar) system, named "Dardanos", was installed in November 2009 on the eastern coast of Lemnos Island, North Aegean Sea, to monitor the surface inflow of Black Sea waters exiting from the Dardanelles Strait, as well as to constitute a coastal management tool for incidents of oil-pollution or search-and-rescue operations. Strong interference from external radio signals has been a source of noise deteriorating the quality of the backscattered signal, thus significantly reducing the HF radar's effective operating range. In order to ameliorate this problem, further quality-control and data gap interpolating procedures have been developed and applied, to be used in addition to the procedures incorporated and used by the manufacturer's signal processing software. The second-level processing involves traditional despiking in the temporal domain, preceding Empirical Orthogonal Function analysis. The latter is used not only to filter high-frequency noise but also to fill data gaps in time and space. The data reconstruction procedure has been assessed via comparison of (a) HF radial versus CODE-type drifter radial velocities as well as (b) HF-derived virtual drifter tracks versus actual drifter tracks. The main circulation features and their variability, as revealed by the reconstructed fields, are presented.

Surface currents in the Porsanger fjord in northern Norway

“…WERA system applied in this study has been developed at the University of Hamburg in 1996, and demonstrated robust accuracy and reliability at numerous installation sites (e.g., Helzel et al 2010Helzel et al , 2011Kokkini et al 2014). In our experiment, WERA system was used in a phased-array mode, advantageous in fjord environment where spatial and temporal variability of surface currents is relatively high.…”

“…These systems are now widely accepted by the oceanographic community as an efficient tool and are routinely used by many U.S. and European oceanographic research organizations (see for example the Southern California Coastal Ocean Observing System at www.sccoos.org). The performance of HF radars has been extensively tested by comparisons with moored ADCPs, ship mounted ADCPs, drifters and models (e.g., Carbajal and Pohlmann 2004;Chapman et al 1997;Kaplan et al 2005;Kohut and Glenn 2003;Kokkini et al 2014;Ohlmann et al 2007;Shay et al 2008;Parks et al 2009;Robinson and Wyatt 2011). For example, comparisons of ADCP and WERA (Wellen Radars) estimates of surface currents at the observation network in the German Bight showed that the standard deviation between the two estimates was less than 0.1 ms -1 and the bias was -0.004 ms -1 .…”

A multiplatform investigation of Istrian Front dynamics (north Adriatic Sea) in winter 2015

“…In the Aegean Sea, offshore the eastern part of Limnos Island, an intense thermohaline front is formed between the Black Sea outflow from the Dardanelles and the Levantine Intermediate Water (LIW), which is advected from the south (Zervakis et al, 2004;Androulidakis & Kourafalou, 2011;Vervatis et al, 2011;Kokkini et al, 2014). In the eastern Alboran Sea, the Almeria -Oran convergent density front is controlled by the size and position of the Eastern Alboran Sea gyre .…”

Validation of Sensing Ocean Surface Currents Using Multi-Frequency HF Radar Based on a Circular Receiving Array

“…Many studies comparing HF radar current measurements with in situ current measurements have been developed by researchers interested in radar performance [16][17][18][19][20][21]. Other studies that compare HF radar-derived currents with drift buoy data were also conducted over the past several years [22][23][24][25][26]. More recently, studies have been performed to develop a method of calibrating the receiving antenna (array), and promising results have also been reported for direction-finding and beam-forming HF radar systems [27].…”