ABSTRACT
Feasible methods that might be used to decompose wave groups are Fourier transform, wavelet transform (Chan 1995), and empirical mode decomposition (EMD) analysis (Huang et al. 1998, 1999). For a continuous uniform wave group, in which the wave group arises from the superposition of continuous constant-amplitude cosine waves, Fourier transform can distinguish the frequencies of all the components accurately. For an intermittent wave group, in which the wave group arises from the superposition of intermittent cosine waves, Fourier transform can yield only a collection of frequencies that will not represent the actual components. The reason is that Fourier transform is a high-resolution frequency detector with no resolution in the time domain; as a result, the intermittency of wave groups will show as additional frequencies in the spectrum, and the actual frequencies of the wave components will be altered to new locations.
