Wavelet Spectrum of Freak Waves in the Ocean

Abstract

This paper presents a wavelet transform analysis of continuous wave recordings in the Sea of Japan during 1986 1990. The analysis is carried out to study the incidents of freak waves. The results show that a well-defined freak wave can be readily identified from the wavelet spect rum where strong energy density in the spectrum is instantly surged and seemingly carried over to the high frequency components at the ins tant the freak wave occurs. Thus for a given freak wave, there appears a clear corresponding signature shown in the time-frequency wavelet spectrum. Since freak waves are primarily transient events occurring unexpectedly, wavelet transform analysis on continuous, long duration wave measurements clearly represents the most ideal approach to discern the localized characteristics of freak waves for further exploration. 1 I n t r o d u c t i o n Coasta l and open oceans are known to have occasionally observed waves of unusually large size, generally known as the freak waves, which can be hazardous to mariners . As the occurrence of freak waves has been mostly during unknown and unexpec ted conditions, available measurement and analysis are extremely rare. Because of i ts rareness and lack of measurement , nei ther the cause of the occurrence nor a specific definition of freak waves have been sufficiently