Sub-daily polar motion from GPS, GLONASS, and Galileo

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.

Orbital Artifacts in Multi‐GNSS Precise Point Positioning Time Series

“…The origin of these signals is most likely in satellite orbits/clocks with smaller contributions from geophysical and multipath signals. Not only do the signals appear in PPP series but also in other GNSS‐based products, for example, K 1 harmonic signals are visible in the time series of high‐frequency Earth rotation parameters derived in the processing of double‐differenced GPS observations collected by a global network of stations (Rothacher et al., 2001; Sibois, 2011; Zajdel et al., 2021b).…”

“…Zajdel et al. (2021b) provided details on the expected orbital periods for GPS, GLONASS, and Galileo systems.…”

“…However, when stacking subdaily ZTD estimates from all the stations, the signals at the harmonics of the sidereal day are visible, with the amplitude reaching 1.3 mm for the 23.93 hr period (K 1 ). Earth rotation parameters derived in the processing of double-differenced GPS observations collected by a global network of stations (Rothacher et al, 2001;Sibois, 2011;Zajdel et al, 2021b).…”

“…This dependency shall be expressed as follows, after Zajdel et al (2019): where T S is satellite revolution period, T E is Earth rotation period (∼23.9345 hr), and P nm is an orbital period for selected n,m terms. Zajdel et al (2021b) provided details on the expected orbital periods for GPS, GLONASS, and Galileo systems.…”

“…Spurious signals might originate from deficiencies in the background geodynamical models used in the processing or deficiencies in orbit modeling, especially nongravitational perturbing forces, such as solar radiation pressure (SRP). The artifactual signals found in the GNSS‐based products may be classified into five groups: (1) mismodeling of the long‐period tides (Abraha et al., 2018; Klos et al., 2021; Steigenberger et al., 2009; Tregoning & van Dam, 2005; Watson et al., 2006), (2) aliasing of subdaily signals through the daily GNSS solutions, (3) repeat period of satellite orbits (Abraha et al., 2017; Griffiths & Ray, 2013; King et al., 2003, 2008; Penna & Stewart, 2003), (4) draconitic errors due to the repeat period of the orbital plane orientation with respect to the Sun (Ray et al., 2008), (5) the resonance between the Earth rotation and satellite revolution period (Hadas & Hobiger, 2020; Zajdel et al., 2021b). Finally, stations respond to the local environmental issues reaching centimeters in effects, for example, snow and ice cover, soil moisture or vegetation growth, and local multipath (Chanard et al., 2020).…”