The extraction of harmonic tidal constants from high and low waters

With the application of electronic computers, the extraction of harmonic constants from high and low waters becomes an extremely simple process as compared with Doods’n’s technique. The phenomenon of aliasing is examined by supposing the samples are taken at intervals of exactly 6 lunar hours. The constituents with frequencies satisfying the relation are inseparable and the coefficient determinant of the normal equations will be singular if the heights only are used. When the values of the first derivatives and the irregularity of the sampling are taken into consideration the condition of the determinant is improved. Large diurnal tides can cause irregularity of sampling and so we are in favour of the separation of the aliased constituents. For tidal current data, if the slack times are available, the results of analysis can be much improved. The results for major constituents derived from the observed high and low waters agree satisfactorily with those from hourly data. This paper was published in Chinese inOcean. Limn. Sinica 17(4):318–328, 1986.