Wave measurements with an ADCP

A standard four beam 1.2 MHz ADCP was deployed in a sea bed frame in Red Wharf Bay, off Anglesey in the Irish Sea, in a water depth of 23 m at low water. The instrument sampled every 2 seconds, for 25 hours, recording beam data in 20 one metre bins from 3.6 to 22.6 m above the bed. The beams were at 20 degrees to the vertical. Wave activity, with peak periods of between 5 and 6 seconds, was detected in the top bins throughout the record. The largest wave activity occurred during the first four hours, coinciding with low water, when wave orbital velocities were twice as large as for the rest of the deployment. During this period the activity was detected in all current bins, decreasing exponentially with depth, and also in the back-scattered signal strength recorded by the top two bins, which at low water experienced sidelobe interference from the surface return. The measurements have been applied to obtaining wave information by studying the along beam wave orbital velocities, the phase differences between the beams for the estimation of wave direction and the phase differences between the elevation and current signals