No abstract

No abstract

High Frequency Radar (HFR) is a land-based remote sensing instrument offering a unique insight to coastal ocean variability, by providing synoptic, high frequency and high resolution data at the ocean atmosphere interface. HFRs have become invaluable tools in the field of operational oceanography for measuring surface currents, waves and winds, with direct applications in different sectors and an unprecedented potential for the integrated management of the coastal zone. In Europe, the number of HFR networks has been showing a significant growth over the past 10 years, with over 50 HFRs currently deployed and a number in the planning stage. There is also a growing literature concerning the use of this technology in research and operational oceanography. A big effort is made in Europe toward a coordinated development of coastal HFR technology and its products within the framework of different European and international initiatives. One recent initiative has been to make an up-to-date inventory of the existing HFR operational systems in Europe, describing the characteristics of the systems, their operational products and applications. This paper offers a comprehensive review on the present status of European HFR network, and discusses the next steps toward the integration of HFR platforms as operational components of the European Ocean Observing System, designed to align and integrate Europe's ocean observing capacity for a truly integrated end-to-end observing system for the European coasts.

Wind fields retrieved from high-resolution synthetic aperture radar (SAR) images are valuable in wind resource assessment offshore. In contrast to in situ measurements, SAR wind maps provide spatial information which allows wind farm developers to compare the wind resource for different sites. Further advantages include the opportunity to obtain archived data and a low cost of satellite based assessments compared to the cost of installing a meteorological mast offshore. Using accurate inputs of wind speed is crucial in wind resource assessment, as predicted power is proportional to the wind speed cubed. Wind speeds retrieved from a series of 97 high-resolution ERS-2 SAR and Envisat ASAR images, at moderate wind speeds (2-15 m s-1), were validated against in situ measurements from an offshore mast in the North Sea. The wind direction input, necessary for SAR wind speed retrievals, was obtained from the meteorological mast and from a local gradient analysis of streaks in the SAR images. For the first method, a standard deviation of ~1.1 m s-1 was found. The second method, which worked independently of in situ measurements, yielded a standard deviation of ~1.3 m s-1. The performance of three geophysical model functions was compared. The best approximation to the in situ measurements of wind speed was found for CMOD-IFR2, despite a bias on the order of-0.3 m s-1. CMOD4 retrievals also underestimated the wind speed, whereas the bias on CMOD5 retrievals was negligible. The accuracy on SAR wind retrievals improved as cases with a long fetch and near-neutral atmospheric stability were analyzed separately. The mean wind speed, obtained from the 97 SAR scenes, was linked closely to the bias on SAR wind retrievals. Agreement to ±15% of the in situ measurements was found for all the wind retrieval methods tested.

No abstract

No abstract

No abstract

The Lagrangian Submesoscale Experiment (LASER) involved the deployment of ~1000 biodegradable GPS-tracked Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE) drifters to measure submesoscale upper-ocean currents and their potential impact on oil spills. The experiment was conducted from January to February 2016 in the Gulf of Mexico (GoM) near the mouth of the Mississippi River, an area characterized by strong submesoscale currents. A Helmholtz-Zentrum Geesthacht (HZG) marine X-band radar (MR) on board the R/V F. G. Walton Smith was used to locate fronts and eddies by their sea surface roughness signatures. The MR data were further processed to yield near-surface current maps at ~500-m resolution up to a maximum range of ~3 km. This study employs the drifter measurements to perform the first comprehensive validation of MR near-surface current maps. For a total of 4130 MR–drifter pairs, the root-mean-square error for the current speed is 4 cm and that for the current direction is 12°. The MR samples currents at a greater effective depth than the CARTHE drifters (1–5 m vs ~0.4 m). The mean MR–drifter differences are consistent with a wave- and wind-driven vertical current profile that weakens with increasing depth and rotates clockwise from the wind direction (by 0.7% of the wind speed and 15°). The technique presented here has great potential in observational oceanography, as it allows research vessels to map the horizontal flow structure, complementing the vertical profiles measured by ADCP.