Complex demodulation in VLBI estimation of high frequency Earth rotation components |
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| Institution: | 1. Institute of Geodesy and Geophysics, Vienna University of Technology, Gußhausstraße 27-29, 1040 Vienna, Austria;2. Department of Geodesy and Cartography, Warsaw University of Technology, Pl. Politechniki 1, 00-661 Warsaw, Poland;3. Space Research Centre, Polish Academy of Sciences, Bartycka 18A, 00-716 Warsaw, Poland;1. Adam Mickiewicz University in Poznań, Institute of Geology, Poland;2. University of Warsaw, Faculty of Geography and Regional Studies, Poland;1. Universidade Federal Rural de Pernambuco, Departamento de Estatística e Informática, Rua Dom Manoel de Medeiros s/n, Dois Irmãos, 52171-900 Recife/PE, Brazil;2. National Research Council, Institute of Methodologies for Environmental Analysis, C.da S.Loja, Tito 85050, Italy;1. Geosciences department, Institut polytechnique LaSalle Beauvais, 19, rue Pierre-Waguet, 60000 Beauvais, France;2. Équipe B2R Département des géosciences, Institut polytechnique LaSalle Beauvais, 19, rue Pierre-Waguet, 60000 Beauvais, France;3. UP 2012-10-103 PICAR-T, Institut polytechnique LaSalle Beauvais, 19, rue Pierre-Waguet, 60000 Beauvais, France;4. Syndicat mixte Baie de Somme, Grand Littoral picard, 1, place de l’Amiral-Courbet, 80142 Abbeville, France;1. Astronomical Institute, Czech Academy of Sciences, Fri?ova 298, 251 65 Ond?ejov, Czech Republic;2. ESA/ESRIN, Via Galileo Galilei, 00044 Frascati, Italy |
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| Abstract: | The spectrum of high frequency Earth rotation variations contains strong harmonic signal components mainly excited by ocean tides along with much weaker non-harmonic fluctuations driven by irregular processes like the diurnal thermal tides in the atmosphere and oceans. In order to properly investigate non-harmonic phenomena a representation in time domain is inevitable. We present a method, operating in time domain, which is easily applicable within Earth rotation estimation from Very Long Baseline Interferometry (VLBI). It enables the determination of diurnal and subdiurnal variations, and is still effective with merely diurnal parameter sampling. The features of complex demodulation are used in an extended parameterization of polar motion and universal time which was implemented into a dedicated version of the Vienna VLBI Software VieVS. The functionality of the approach was evaluated by comparing amplitudes and phases of harmonic variations at tidal periods (diurnal/semidiurnal), derived from demodulated Earth rotation parameters (ERP), estimated from hourly resolved VLBI ERP time series and taken from a recently published VLBI ERP model to the terms of the conventional model for ocean tidal effects in Earth rotation recommended by the International Earth Rotation and Reference System Service (IERS). The three sets of tidal terms derived from VLBI observations extensively agree among each other within the three-sigma level of the demodulation approach, which is below 6 μas for polar motion and universal time. They also coincide in terms of differences to the IERS model, where significant deviations primarily for several major tidal terms are apparent. An additional spectral analysis of the as well estimated demodulated ERP series of the ter- and quarterdiurnal frequency bands did not reveal any significant signal structure. The complex demodulation applied in VLBI parameter estimation could be demonstrated a suitable procedure for the reliable reproduction of high frequency Earth rotation components and thus represents a qualified tool for future studies of irregular geophysical signals in ERP measured by space geodetic techniques. |
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