Observation of the Power Spectrum of Ocean Waves Using a Cloverleaf Buoy

Abstract

The power spectra of typical sets of ocean wave data obtained in the open ocean using a cloverleaf buoy are analyzed to determine an idealized form for the spectrum of ocean surface waves. It is shown that most of the single-peaked spectra observed in a generation area can be described well by the spectral form of the JONSWAP type. Two parameters α and ? characterizing the spectral form are calculated for each spectrum measured. Their relations to the dimensionless peak frequency f?m (=fmU/g) are then determined. These relations are further converted into fetch relations for α and ? through a relation between f? and a dimensionless fetch F? (=gF/U2). Another spectral form proposed by Toba (1978) is examined and shown to fit as well to the observed spectra at high frequencies This fact shows quasi-equivalence of the JONSWAP spectrum and Toba's spectrum in the high-frequency range. On the basis of the agreements of both spectral forms at high frequencies, properties of the dimensionless constant α&prime in Toba's spectrum are examined. It is shown that α&prime depends very weakly on the dimensionless fetch F?.