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Ann. Geophys., 24, 1483-1491, 2006
www.ann-geophys.net/24/1483/2006/
© European Geosciences Union 2006
The influence of digitisation and timing errors on the estimation of tidal components at Split (Adriatic Sea)
I. Vilibic
Institute of Oceanography and Fisheries, Šetalište I. Meštrovića 63, 21000 Split, Croatia
Abstract. The paper comprises the calculations of amplitudes and phases of tidal
harmonic constituents, performed on hourly sea level data recorded at the Split
tide gauge in the period 1957-2001. Interannual changes in all constituents
have been detected, stronger in phases than in amplitudes. For example, the
estimated change in M2 amplitude and phase is 22% (1.31 cm) and
24.9° between the 1962–1978 and 1957–1961 periods, 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). This is the reason why the M2 and K1 amplitudes were
recomputed with 3–4 mm larger values using newer software, thereby decreasing their
standard deviation by 60–70% in the 1986–1995 period. Artificial errors may
be reduced by the upgrading of digitising software; however, most of the errors
still remain in the series. These errors may have repercussions when trying
to explain some unusual findings: the energy of de-tided sea level series at
the 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.
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