Estimation of Infragravity Wave Spectrum with Variable Parameter Related to Properties of Wind Wave

Abstract

It is well known that a correlation between infragravity wave heights and the properties of wind waves observed in offshore harbor. Hirasihi et al (1997) have proposed a function of infragravity wave spectrum related to a function of wind wave spectrum by a boundary frequency estimated with parameter: α_l. The α_l can be estimated with the square root of ratio of infragravity wave energy to total wave energy: R_L. In this study, a related function between α_l and R_L for JONSWAP spectrum is proposed and it is confirmed that an averaged value of α_l estimated with spectra observed in storm conditions at each observation station may overestimate the infragravity wave heights in calm conditions. Moreover, the related function between Ursell number and α_l proposed Hirayama et al (2014) can estimate them with good accuracy.