A COMPARISON OF DIRECTIONAL BUOY AND FIXED PLATFORM MEASUREMENTS OF PACIFIC SWELL

The performance of the Datawell Directional Waverider and the National Data Buoy Center.(NDBC) 3-m discus buoy, widely used to measure the d irectional 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 accura cy of the platform ground-truth army was verified by close agreement o f wavenumber estimates with the theoretical linear dispersion relation for surface gravity waves. Buoy and army estimates of wave energy and directional parameters, based on integration of the directional momen ts across' the frequency band of energetic swell (0.06-0.14 Hz), are c ompared for a wide range of wave conditions. Wave energy and mean prop agation direction estimates from both buoys agree well with the platfo rm results. However, the Datawell buoy provides significantly better e stimates of directional spread and skewness than the NDBC buoy.