Validation of surface current measurements in the Northern Adriatic Sea from High-Frequency radars

The performances of a shore-based high-frequency (HF) radar network deployed along the coast of theVenice lagoon (northern Adriatic Sea) are discussed based on a comparison with a single bottom-mountedADCP deployed in the shallow-water area offshore of the lagoon for a 40-day period in August–September2005.The analyses, carried out using currents representative of the first meter for the HF radars and 2.5 m for theADCP, gave rms differences of radial currents in the range of 8.7–14.7 cm/s (correlation 0.37– 0.82) for theideal pattern and 8.4–20.5 cm/s (correlation 0.14–0.84) for the measured pattern. Good correlation wasfound between surface current vectors and moored data (scalar correlation up to R=0.83, vector correlationr=0.78, veering angle 68). Comparison metrics were improved for the low-passed currents. Angular offsetsranged between +16 and +11. Differences depended primarily on the geophysical variability within thewater column. Bearing offsets also contributed because they lead to comparisons with radial velocities aterroneous angular sectors.Radar performances were severely affected by strong northeasterly wind pulses in their early stages. Anincreased broadband noise, spread over the entire Doppler spectrum across all ranges to the antennas,masked the Bragg peaks and determined the loss in radar coverage, introducing gross underestimations ofboth radial velocities and total currents.