Effect of intrinsic and sampling variability on wave parameters and wave statistics

Abstract

Significant wave height and zero-crossing wave period are used for validation of wave models, wave climate studies, and calculations of extremes for weather forecasting purposes. They represent also important parameters for design and operations of ships and offshore structures. They can be evaluated using 20 or 30-min long wave recordings directly or using the wave spectrum. Spectral methods often reduce the 20 min to about 17 min. Due to the limited duration of wave records, estimates of significant wave height and zero-crossing wave period are affected by sampling variability, the statistical uncertainty due to limited number of observations. The study provides estimates of sampling variability associated with significant wave height and zero-crossing wave period based on measurements from the Ekofisk field in central North Sea. Further, it demonstrates the impact of intrinsic and sampling variability has on short-term and long-term description of ocean waves as well as validation of wave spectral models.

Appendix A—sampling variability

Tables and include sampling variability standard deviations of the significant wave height and zero-crossing wave period, respectively, for the Northern North Sea scatter diagram calculated by Bitner-Gregersen and Hagen (1990). Assuming Gaussian sea surface and the JONSWAP spectrum with γ = 3.3. The results are valid for any worldwide location under the adopted assumptions.

Table 1 The sampling variability standard deviation ${\sigma}_{H_{{}_{m0}}}$ (in %) of H _m0 for the JONSWAP spectrum (Bitner-Gregersen and Hagen 1990)

Table 2 The sampling variability standard deviation ${\sigma}_{T_{{}_{m0}}}$ (in %) of T _m02 for the JONSWAP spectrum (Bitner-Gregersen and Hagen 1990)