DIRECTIONAL SPECTRUM CHARACTERISTICS OBSERVED AT AN OFFSHORE OBSERVATION TOWER AND THE CORRELATION WITH WIND FIELD

Abstract

 In this study, directional wave spectra observed every 20 minutes by an ADCP installed on an offshore observation tower were analyzed to classify energy distribution characteristics and dominant wave directions, followed by a correlation analysis with wind data. Wave system separation was conducted using the WITS method, where cases in which the first component accounted for more than 75% of the total energy were defined as Unimodal, and others as Complex-field. Unimodal wave systems were dominant in the northwest direction within a wave age below 30, whereas in the southwest direction, data were distributed across a broader wave age range, with a higher occurrence rate of Complex-field systems. Additionally, the relationship between nondimensional fetch and nondimensional significant wave period theoretically follows a 1/3 power law. The observational data showed a smaller slope than this theoretical value for waves from the northwest, while a larger slope was observed for waves from the southwest.