engleski

The influence of digitisation and timing errors on the estimation of tidal components at Split (Adriatic Sea)

The paper comprises the calculations of amplitudes and phases of tidal harmonic constituents, performed on hourly sea level data recorded at Split tide gauge in the period 1957-2001. Interannual changes in all constituents have been detected, stronger in phases than in amplitudes. For example, estimated change in M2 amplitude and phase is 22% (1.31 cm) and 24.9o between 1962-1978 and 1957-1961 period, respectively. Some of the differences are generated artificially throughout the measurements (clock errors, positioning and stretching of a chart) and within the digitising procedure, rather than by natural processes and changes (e.g. changes in mean sea level). That is the reason why M2 and K1 amplitudes were recomputed with 3-4 mm larger values using newer software, decreasing their standard deviation for 60-70% in 1986-1995 period. Artificial errors may be reduced by upgrading of digitising software ; however, most of the errors still remain in the series. These errors may have a repercussion when trying to explain some unusual findings: the energy of de-tided sea level series at M2 tidal period (12.4 h) has been assumed previously to be a result of nonlinear coupling, but it may be caused, at least partly by, timing errors in the time series.

Instruments and techniques; Surface waves and tides; General or miscellaneous

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