DIRECTIONAL OCEAN WAVE SPECTRA USING BUOY AZIMUTH, PITCH, AND ROLL DERIVED FROM MAGNETIC-FIELD COMPONENTS

Hull slopes resulting from wave motion are needed to estimate directional wave spectra from the motions of a buoy. To reduce the cost and size of onboard sensors, these slopes can be determined from measurements of the magnetic field components inside the hull along two orthogonal axes parallel to the deck of a buoy. Algorithms are developed for estimation of azimuth, pitch, and roll angles using these measurements. The algorithms account for residual and induced hull magnetism. Azimuth, pitch, and roll, as well as estimates of directional wave spectra, are determined both from the magnetic field measurements and from a conventional wave measurement system on the same buoy. Comparisons show that estimates of directional spectra based on magnetometer-derived pitch and roll agree well.