This project is a collaborative activity between Department of Marine Science, Aegean University and HCMR Institute of Oceaonography.

The CORI surface currents measuring system has been implemented in the framework of the CORI (Prevention and Management of Sea Originated Risks to the Coastal Zone) INTEREG IIIB ARCHIMED 2000-2006 programme in cooperation with the Department of Marine Science of the Aegean University. It uses a WERA HF Remote Sensing system (Helzel Messtechnik GmbH, Germany ) transmitting electromagnetic waves in the range of 6 - 30 MHz to measure surface current velocities and optionally ocean wave height and wind.

The transmitted vertical polarized electromagnetic wave travels along the sea surface beyond the horizon and is backscattered by ocean waves of half the electromagnetic wavelength (Bragg Scattering) and the system infers the speed of the surface currents carrying the waves by measuring the Doppler spectrum caused by moving ocean waves. The surface currents measurements obtained from the WERA system represent the integral of the actual currents in the top meter (or less) of the water column.

The CORI system has been deployed since June 2009 on the east coast of Limnos Island, measuring surface currents in front of Dardanelles Straits every 30 minutes. It comprises by two sub-systems (units) deployed ~23 km apart in order to get the full 2D near surface currents field (figure 1). Each sub-system has four transmit and four receive antenna elements (a 4-element square array of receiving antennas can be used if only surface currents are to be measured) and makes independent measurements of current speeds along radials emanating from its phased-array antenna system. The system working frequency is at 13.544 MHz for which the Bragg frequency is at 0.375 Hz in deep water, corresponding to a 11.08m wavelength. The Bragg scattering effect in the absence of surface currents results in two well defined spectral peaks (Bragg peaks) at ±0.375 Hz which in the case of surface current with radial component V are displaced from Bragg frequency by an amount Δf=(2/22.16)*V. The system emits a chirped continuous wave with a repetition frequency of 3.85 Hz and a 50 kHz bandwidth which gives a radial resolution of 3 km.