The present paper intends to compare the satellite data provided by the CLIOSat data base with the Global Wave Statistics as well as WRB data, and to asses the variation in the long-term load responses and fatigue damage arising from use of the different data types. The North Atlantic ship route is considered. In the first part of the paper, methods for derivation of Tz estimates from SAR image spectra are discussed. Further, the Tz estimates are compared with the Global Wave Statistics periods and WRB data. Finally, case studies illustrating the uncertainty in response characteristics arising from use of the Global Wave Statistics and satellite wave data are given.
The joint long-term distribution of significant wave height, Hs, and average zero-crossing wave period, Tz, represents an important characteristic for prediction of design and operational conditions of ship and offshore structures. Up to now, the data sources for these statistics were limited to instrumental measurements, most of them nearshore, to ship masters" observations, conveniently compiled into Global Wave Statistics atlas, Hogben et al. (1986), and to hindcast model results. The accuracy of these data is varying. Recently, in several papers, the comparison of the Global Wave Statistics (GWS) data with the instrumental/hindcast data has been presented. However, some doubt remains concerning the GWS data accuracy, especially wave period, confer e.g. Guedes Soares and Moan (1991), Chen and Thayamballi (1991) and Bitner-Gregersen et al. (1993, 1994, 1995). These studies have indicated that the GWS data may both underestimate as well as overestimate the significant wave height, and for large hs they may underestimate the mean zero-crossing wave period while overestimate for low hs For instance, Bitner-Gregersen et al. (1995) suggested to adjust the North Atlantic and world-wide GWS data using the instrumentally measured/recommended average wave steepness as a reference value.
