Wave Groupiness in the Nearshore Area by Hilbert Spectrum

The Empirical Mode Decomposition (EMD) method for nonlinear and non-stationary time series analysis, also known as Huang Hilbert Transform (HHT), is applied to wave field data from the nearshore area. The frequency-time distribution of the energy, designed as a Hilbert spectrum is utilized for examination of the group structure of the sea waves. The necessary condition for existence of wave grouping is determined on the base of the results of empirical mode decomposition of the data. The HHT method provides a unique basis for expansion of the data, derived from and based on the data. The variations of the group characteristics across the shore are examined and their relationship with the local wave characteristics is investigated outside and inside the surf zone. The Hilbert spectrum provided new insights on the wave and group transformation in the cross-shore direction.