Estimation of the Free Core Nutation parameters from SG data: Sensitivity study and comparative analysis using linearized least-squares and Bayesian methods |
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| Institution: | 1. Institute of Mechanics, Materials and Civil Engineering (IMMC), Université catholique de Louvain, Avenue Georges Lemaître 4, B-1348 Louvain-la-Neuve, Belgium;2. Royal Observatory of Belgium, Avenue Circulaire 3, B-1180 Bruxelles, Belgium;3. Space Exploration Sector, Johns Hopkins Applied Physics Laboratory, Laurel, MD 20723, USA;5. Université catholique de Louvain, Institute of Mechanics, Materials and Civil Engineering (IMMC) & Earth and Life Institute (ELI), Avenue Georges Lemaître 4, B-1348 Louvain-la-Neuve, Belgium;6. Delft Institute of Applied Mathematics (DIAM), Delft University of Technology, Mekelweg 4, 2628CD Delft, The Netherlands;1. Dipartimento di Ingegneria dell’Informazione ed Elettrica e Matematica Applicata, Università di Salerno, Via Giovanni Paolo II, Fisciano 84084, SA, Italy;2. Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Napoli - Osservatorio Vesuviano, Via Diocleziano 328, Naples 80124, Italy |
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| Abstract: | The Free Core Nutation (FCN) is investigated with the help of its resonance effect on the tidal amplitudes in Superconducting Gravimeter (SG) records of the GGP network. The FCN resonance parameters are combined in a resonance equation involving the Earth's interior parameters. The sensitivity of the FCN parameters to the diurnal tidal waves demonstrates that the quality factor of the FCN is strongly dependent on the accuracy of the imaginary part estimates of the gravimetric factors close to the resonance. The weak amplitude of Ψ1 tidal wave on the Earth, which is the closest in frequency to the FCN, in addition to errors in ocean loading correction, explains the poor determination of the quality factor Q from surface gravimetric data. The inversion of tidal gravimetric factors leads to estimates of the period, Q and resonance strength of the FCN. We show that, by inverting log(Q) instead of Q, the results using the least-squares method optimized using the Levenberg–Marquardt algorithm are in agreement with the Bayesian probabilistic results and agree with the results obtained from VLBI nutation data. Finally, a combined inversion of 7 GGP European SG data is performed giving T = 428 ± 3 days and 7762 < Q < 31,989 (90% C.I.). An experimental estimate of the internal pressure Love number is also proposed. |
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