Development of a MATLAB-based toolbox for tide Gauge records using Hilbert-Huang transform

Jamali, Aydin
Tidal records are usually processed on the basis of Harmonic Analysis which in fact works well for linear and stationary data. It is a mathematical procedure which divides the data in a finite number of harmonic constituents. But the tidal data is in reality non-linear and non-stationary because of atmospheric and meteorological parameters. Therefore in this work a MATLAB –based Toolbox has been developed for hourly tidal data collected from four tide gauge stations at the Turkish costs using Hilbert Huang Empirical Mode Decomposition (HHEMD) which is an efficient and powerful method for non-linear and non-stationary time series. Hilbert Huang Empirical Mode Decomposition (HHEMD) is carried out in two steps. Firstly data are processed by Empirical Mode decomposition (EMD) which decomposes the signal in a number of intrinsic mode components (IMFs). The second step is to apply the Hilbert transform to each IMF in order to find Phase, Amplitude and Instantaneous Frequency of the signal. In this study the hourly tidal data are decomposed in tidal and sub-tidal components using HHEMD and the results of the tidal components are compared with the results of harmonic analysis. Very long and non-stationary period components are filtered as sub tidal. Finally the frequency and amplitude of the diurnal and semi-diurnal component are used to extract the minimum and maximum velocities of the diurnal and semidiurnal tidal constituents in order to analyze the capability of producing tidal energies from possible tidal turbines to be located at tidal stations. Also an exemplarity completeness test has been performed to validate the decomposition of the time series obtained by the Antalya station utilizing EMD. The result showed that the signal has been recovered properly.