Abstract
We derive an empirical model of the sub-daily polar motion (PM) based on the multi-GNSS processing incorporating GPS, GLONASS, and Galileo observations. The sub-daily PM model is based on 3-year multi-GNSS solutions with a 2 h temporal resolution. Firstly, we discuss differences in sub-daily PM estimates delivered from individual GNSS constellations, including GPS, GLONASS, Galileo, and the combined multi-GNSS solutions. Secondly, we evaluate the consistency between the GNSS-based estimates of the sub-daily PM with three independent models, i.e., the model recommended in the International Earth Rotation and Reference Systems Service (IERS) 2010 Conventions, the Desai–Sibois model, and the Gipson model. The sub-daily PM estimates, which are derived from system-specific solutions, are inherently affected by artificial non-tidal signals. These signals arise mainly from the resonance between the Earth rotation period and the satellite revolution period. We found strong spurious signals in GLONASS-based and Galileo-based results with amplitudes up to 30 µas. The combined multi-GNSS solution delivers the best estimates and the best consistency of the sub-daily PM with external geophysical and empirical models. Moreover, the impact of the non-tidal spurious signals in the frequency domain diminishes in the multi-GNSS combination. After the recovery of the tidal coefficients for 38 tides, we infer better consistency of the GNSS-based empirical models with the new Desai–Sibois model than the model recommended in the IERS 2010 Conventions. The consistency with the Desai–Sibois model, in terms of the inter-quartile ranges of tidal amplitude differences, reaches the level of 1.6, 5.7, 6.3, 2.2 µas for the prograde diurnal tidal terms and 1.2/2.1, 2.3/6.0, 2.6/5.5, 2.1/5.1 µas for prograde/retrograde semi-diurnal tidal terms, for the combined multi-GNSS, GPS, GLONASS, and Galileo solutions, respectively.
Highlights
Polar motion (PM) is a wobble of the spin axis of the Earth about its figure axis
We assess the consistency of our empirical Global Navigation Satellite Systems (GNSS) sub-daily PM models w.r.t. external models of sub-daily PM, including the International Earth Rotation and Reference Systems Service (IERS) 2010 Conventions model (Petit and Luzum 2010), the Desai–Sibois model based on the altimetric ocean tide TPXO.8 model (Desai and Sibois 2016), and the Gipson model derived from Very Long Baseline Interferometry (VLBI) data (Gipson 2017)
As we demonstrated in the previous sections, each of the system-specific solutions is partly affected by the impact of the artificial signals at the orbital periods, which may lead to inconsistencies at the particular tidal lines
Summary
Polar motion (PM) is a wobble of the spin axis of the Earth about its figure axis. In space geodesy, PM is observed as a variation in the true pole at the surface of the Earth, represented by the pole coordinates, around the mean pole. Besides different revolution periods of various GNSS satellites, two Galileo satellites have an eccentric orbit, which may help to decorrelate tidal constituents from orbit parameters and reveal the GPS-based errors in sub-daily ERP estimates. The main emphasis of this contribution is to evaluate the suitability of different GNSS constellations, including GPS, GLONASS, and Galileo, to the estimation of sub-daily PM and the reliability of the PM models based thereon. We assess the consistency of our empirical GNSS sub-daily PM models w.r.t. external models of sub-daily PM, including the IERS 2010 Conventions model (Petit and Luzum 2010), the Desai–Sibois model based on the altimetric ocean tide TPXO. model (Desai and Sibois 2016), and the Gipson model derived from VLBI data (Gipson 2017)
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