The University of Plymouth owns and operates a high-frequency (HF) ocean Wellen radar (WERA) system made up of two stations on the north Cornwall coast. The system has overlooked and measured surface currents and directional wave spectra in the area surrounding the Wave Hub test site for offshore renewable energy since 2011.
Four-element CODAR HF radar systems have been an established method for accurate measurement of offshore currents since the 1980s. The radar returns are sorted by range and azimuth onto a grid of a predetermined resolution. WERA HF systems improve upon CODAR as they make use of a high number of receive antennas (16 at the Wave Hub), enabling beamforming techniques which allow for reliable resolution of surface wave spectra from wave-induced second-order spectral bands. The larger array also allows for greater ranges and a higher spatial resolution than traditional systems. In addition, a single radar station measures just the radial current speed relative to its position, therefore the University’s two WERA arrays allow for the determination of the two-dimensional current vector. Some nations including the USA and Australia operate nationwide radar networks as an effective method for regular monitoring of offshore currents, however the Wave Hub system is the only 2 station system currently operating in the UK.
Due to the vertical polarisation of the HF signal and the electrically conductive ocean surface, HF systems are capable of measuring further than the line-of-sight and the Wave Hub HF radar measures current velocities up to 100 km from the coast and wave spectra 50 km from the coast. Results from the radar system are provided hourly with a spatial resolution of 1 km.
While the use of HF radars for ocean current measurements has been established for more than 30 years, the special wave measuring capabilities of our WERA setup is a much less mature technology that our research is helping to establish. The maturity of this technology will prove invaluable as the requirement for regular wave measurements over large spatial areas grows from emerging sectors including wave-to-energy renewables; here our system offers distinct advantages over current practice. Wave buoys are limited to single point wave measurements, whereas our radar offers a large spatial coverage. Remote sensing satellites are also outperformed temporally by our radar as the satellites are only overhead to take measurements of the target area for a short period, with gaps between passes on the scale of days to weeks.