A Comparison of Directional Buoy and Fixed Platform Measurements Of Pacific Swell

Abstract

The performance of the Datawell Directional Waverider and the National Data Buoy Center (NDBC) 3-m discus buoy, widely used to measure the directional properties of surface gravity waves, are evaluated through comparisons to an array of six pressure transducers mounted 14 m below the sea surface on a platform in 200-m depth. Each buoy was deployed for several months within a few kilometers of the platform. The accuracy of the platform ground-truth array was verified by close agreement of wavenumber estimates with the theoretical linear dispersion relation for surface gravity waves. Buoy and array estimates of wave energy and directional parameters, based on integration of the directional moments across the frequency band of energetic swell (0.06?0.14 Hz), are compared for a wide range of wave conditions. Wave energy and mean propagation direction estimates from both buoys agree well with the platform results. However, the Datawell buoy provides significantly better estimates of directional spread and skewness than the NDBC buoy.