Measurement of surface currents in Liverpool Bay by high-frequency radar

The backscattering of high-frequency radar echoes from the sea surface can yield useful information about ocean waves and surface currents 1–3 . The Rutherford Appelton Laboratory Ocean Surface Current Radar (OSCR) system is based on the CODAR system 4 but differs significantly in that it uses a beam-forming receive antenna to determine the direction of the backscattered signals instead of using the CODAR direction finding system. OSCR derives a radial component of surface velocity by measuring the shift in recorded spectra associated with advancing and receding waves. In this survey of surface currents in Liverpool Bay, using only OSCR, measurements were made first for 7 days from the Lancashire coast followed, 1 month later, by similar measurements from the Wirral coast. These were combined to compute current ellipses for the predominant M 2 tidal constituent. Spatial distributions of the ellipse parameters agree well with values obtained from a numerical model and from moored current meters. This new observational technique should provide data on the fine structure of near-shore surface currents for use in studies of sediment transport and pollutant dispersal.