Comparisons of the statistical properties of random waves were carried out is this study. Three different sources of data were used for comparison: field data measured in northern Taiwan; wind flume experiments conducted under various wind speeds, and mechanically random waves generated using different target spectra. Statistical properties under considerations are wave heights and period distributions. Relations between various reference wave heights were compared with theoretical relations derived from the Rayleigh assumption. Distributions of periods were fitted to the theoretical, as well as empirical models found in the literature.
Statistical properties of wind-generated random waves are best studied using field data. Since field measurements are generally sparse and the experiments are expansive, other alternatives - such as wind-flume experiments for scientific studies, and mechanical pseudo-random waves for engineering applications - are used instead. However, both these alternatives have their own limitations. Waves generated in flumes using a wind blower, for example, are subjected to side-wall effects (Longuet-Higgins, 1990), bottom friction and pressure gradients along the flume. Most frequently, are the short fetches as compared with waves on the sea surface. In order to generate more mature waves, it is often necessary to operate under rather strong wind conditions. Waves generated by a computer-controlled wave paddle, on the other hand, are often plagued by the presence of second order waves (Gu & Zhou, 1988), as well as other problems such as side-leakage (Hughes, 1993). Since the generating mechanisms, and the constrains they are subjected to, of waves from these sources are different, it is natural to expect that, the statistical properties of these waves should also be different. Evidences that prove this rather intuitive conjecture can be found in the literature. Kimura (1981), for example, used a two-parameter Weibull distribution to study the joint distribution of wave- height and periods of mechanically generated random waves in a laboratory flume.
