Impact of Sampling Variability on Sea Surface Characteristics of Nonlinear Waves

Abstract

The restricted duration of wave records, usually 20 or 30 minutes, introduces sampling variability, the statistical uncertainty due to limited number of observations, in estimates of sea surface characteristics. This uncertainty may have significant impact on derived wave parameters commonly used in design and marine operations, and quantifying it is also of importance for wave forecasting purposes as well as for investigations of extreme wave events such as rogue waves. The study shows, using numerical simulations, effects of sampling variability on the measures of wave field nonlinearity, the skewness and kurtosis coefficients of sea surface elevation, and on the wave crest. Wave data are simulated by the nonlinear wave model HOSM (Higher Order Spectral Method). The Pierson-Moskowitz and the JONSWAP spectrum with different gamma parameters and different directional energy spreading functions are used in the analysis and their effect on sampling variability estimates is demonstrated. Sea states where rogue waves were recorded in nature are considered. The results are compared with the ones obtained from linear wave model simulations. Consequences of sampling variability on description of sea surface nonlinearity are discussed.