ABSTRACT
Real sea waves are nonlinear and nonstationary by nature, and their profile is asymmetrical with respect to the zero level, with sharp crests and flat troughs, especially well pronounced in shallow water. The existence of small ripples riding longer waves, as well as an appearance of many small waves due to wave breaking, complicates the wave profile considerably. Real sea waves also appear in groups, which are time localized transient events. The wave data records always register a mixture of many wave systems with different periods and energy, generated by different sources. Through analysis of sea surface elevation record, we seek to determine characteristic time-frequency scales of the energy. The widely used methods of wave analysis are burdened with the traditional concept of sea waves: as a sine wave with definition domain from minus infinity to plus infinity. It is also assumed, according to linear wave theory, that within the framework of one wave the period is constant and the wave height is equal to twice the wave amplitude. In addition to the positive maxima and negative minima of the wave profile, positive minima and negative maxima are also often observed in the profile of real sea waves. The neglect of these actual features of sea waves leads to incompleteness and misinterpretation of the recorded sea state, and thus the analyzing method can distort the investigated phenomenon.
