Analysis of short and discontinuous tidal data: a case study from the Aegean Sea

An algorithm, which permits to compute the statistically significant tidal constituents and amplitude, duration and frequency of recurrence of meteorological surges, in the case of short, discontinuous or noisy tidal records, is presented. This algorithm is based on step by step filtering techniques and least squares based spectral analysis in both the frequency and time domain, and hence, it permits to avoid, first, the noise introduced in measurements as a result of interpolations, zero padding or fragmentation, and second, large uncertainties introduced by automated tidal computation routines, mainly designed for high tidal amplitudes and high signal to noise ratio data. Additionally, it is simple to follow by non-specialists in oceanic processes. The efficiency of the proposed algorithm is demonstrated on the basis of comparison of annual and interannual, high accuracy and conventional tidal records from the Aegean. This region is characterised by an astronomical tide of the order of 10 cm, about one order of magnitude smaller than the meteorological tide, and hence represents an extreme tidal environment, with very low-signal-to noise ratio values. Such data permit to evaluate the adequacy of an algorithm to successfully analyse records of short duration or with significant gaps, cases in which conventional algorithms fail. The proposed algorithm is therefore suitable for the analysis of recent, high sampling frequency but short duration records, many of which are available online, and for the identification of small amplitude tectonic, oceanographic signals, useful for climatological studies, satellite altimetry calibration or even to test malfunction of instruments.