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Open Access item Spectral analysis of earth tides

Authors:Sukhwani, P. K.
Vieira, Ricardo
Keywords:Earth tides, Mareas terrestres, Geodesia, Geodesy
Issue Date:1978
Publisher:Universidad Complutense de Madrid
CSIC - Centro Coordinado de Mecánica y Astronomía
Citation:Publicación. Seminario de Astronomía y Geodesia, nº 98, 1978.
Series/Report no.:Publicación. Seminario de Astronomía y Geodesia
Abstract:Fourier's method is scarcely used nowadays for the analysis of Earth Tide records since most of the authors working in this field find in this method some disavantages: the long time spent in the computer, the necessity of eliminating the drift before the analysis, the resolution decrease due to those tidal waves whose frequencies are not a multiple of the fundamental frequency of the analysis, the need of large uninterrupted series of records, etc... However, we think that these difficulties can be overcome and that the powerful method of Fourier analysis should not be abandoned. The main ideas for accomplishing it are: the use of a FFT algorithm for which the number of records need not be an integral power of two; several methods for adjusting the drift (for instance, making use of the Legendre polynomials of up to a certain degree, or the method of Pertsev, etc.) and then choose that which gives the least mean square errors for the amplitude ratios and phase lags; the use of the prior knowledge of the frequency of each tidal wave for the computation of the Fourier series to which each wave gives place (seeing that the amplitude and phase of the wave do not affect the "form" of the spectrum) and then set up a system of equations in which the unknowns are the amplitude factor and phase difference of each group of waves, the coeficients affecting these are the harmonics of the above mentioned Fourier series and, the independent terms are the harmonics of the Fourier series of the Earth Tide records; the computation of the effect of the missing records on the spectrum and then making the appropiate convolution to the Fourier series of each wave for taking in account this effect. All this has been programmed and some examples of output from the computer are given, together with the results of the application of the least squares method of analysis for the same records, for comparison of both methods.
Description:Publicado en "Proceedings of the 8th International Symposium on Earth Tides".
Appears in Collections:(IAG) Comunicaciones congresos

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