WAVE AND CURRENT OBSERVATIONS IN A TIDAL INLET USING GPS DRIFTER BUOYS

Abstract

The Wave Resolving Drifter (WRD) Buoy, developed at NPS, was refined by adding an accelerometer and utilizing horizontal Doppler velocity measurements to better resolve the wave surface motions. The WRD Buoy was validated against a Datawell Waverider-GPS buoy by comparing bulk wave statistics, wave energy spectra and wave directional spectra. The validation was performed in deep water, offshore of Monterey Bay, CA. Horizontal measurements from Doppler velocities showed improved capability, particularly in the wind-wave band. Vertical measurements were significantly improved through the addition of the accelerometer. A large array of WRD buoys was deployed in the Golden Gate channel at the entrance to San Francisco Bay and allowed to drift with the outgoing ebb current. The simultaneous deployment of many drifters provides a unique view of the details of the temporal and spatial evolution of the wave field as it propagated through regions of bathymetric and wave-current interactions. Wave heights increased as the wave field propagated over the ebb-tidal shoal and at the entrance to the channel, in the presence of a strong opposing ebb current, as expected. Inside the channel, strong dissipation of high frequency wind waves was observed in the opposing current.