Portilla et al. (2009) pointed out that the overshoot phenomenon in the 1D wave spectrum means the peak amplitude of developing wind sea is greater than that of a fully developed wave with the same peak frequency. Since the PM spectrum mentioned above is a typical wave model of fully developed sea state, it is practical to identify a wave system by comparing the peak value of the corresponding 1D wave spectrum with the peak amplitude of the PM spectrum of the same peak frequency.