Uncertainty in the Estimation of the Directional Wave Spectrum from the Swan and Wavewatch-Iii Models

Abstract

The accuracy of hindcasted directional spectral wave data is not evaluated in many seas due to the lack of spectral wave measurements. As part of this study, a spectral wave measuring buoy was installed on the Utrish coast. The study objective is to define the uncertainties in the estimated wave spectra, considering low-frequency and high-frequency waves. For this purpose, the estimated spectral density distribution and mean spectral direction in terms of spectral frequency bins are assessed based on 14,710 spectral measurements for both SWAN and WAVEWATCH III (WWIII) outputs. The results show that SWAN output fits better the average variance density shape at all frequency ranges f>0.08Hz. However, it somewhat slightly overestimates the variance density in the 0.13-0.17 Hz range. In contrast to the SWAN model, WWIII data show only better accuracy in the 0.13-0.17 Hz frequency range but underestimate the lower frequency energies and overestimate higher frequency ranges.

Keywords: Wave spectra, Spectral wave models, SWAN validation, WWIII validation. Black Sea, ERA5