Abstract
The earth rotation parameters (ERPs) are time-variable global geodetic parameters with a purely geophysical origin. Theoretically, the estimates of these parameters should be independent of the satellite constellation used in GNSS processing. Nonetheless, clear differences in the time series of ERPs are noticed when using different GNSS constellations. In this study, GPS, GLONASS, and Galileo estimates of ERP have been extensively evaluated in search of system-specific signals. Some of the processing details, such as modeling of the direct solar radiation pressure and length of the orbital arc, also have an impact on the ERP estimates. The GPS-based polar motion estimates are of better quality than those based on GLONASS and Galileo, which are susceptible to deficiencies in the orbit modeling. On the other hand, we observe a systematic bias of GPS-based length-of-day (LoD) with respect to the IERS-C04-14 values with a mean offset of − 22.4 µs/day. The Galileo-based solutions are almost entirely free of this issue. The extension of the orbital arc in the GNSS processing from 1 to 3 days is superior for the quality of the ERPs, especially for pole coordinate rates and LoD. The spurious signals inherently influence the Galileo-based and GLONASS-based ERPs at the frequencies which arise from the resonance between the satellite revolution period and earth rotation, e.g., 3.4 days for Galileo and 3.9 days for GLONASS. These and the draconitic signals overshadow the GNSS-based ERP estimates. Although all the system-specific solutions are affected by the artificial signals, the combination of different GNSS mitigates most of the uncertainties and improves the ERP results.
Highlights
The earth rotation parameters (ERPs) belong to the fundamental transformation parameters linking the International Celestial Reference Frame (ICRF) and the International Terrestrial Reference Frame (ITRF) (Petit and Luzum 2010)
The estimates of the X and Y pole coordinates, their rates, and LoD are compared to the reference values of IERS-C04-14 (Bizouard et al 2018)
Bizouard et al (2018) assessed the general consistency of the Global Navigational Satellite System (GNSS)-based IGS results within the IERS-C04-14 combination for the period 2010–2015, which reached an impressive level of 30 μas and 10 μs/day for PM and LoD, respectively
Summary
The earth rotation parameters (ERPs) belong to the fundamental transformation parameters linking the International Celestial Reference Frame (ICRF) and the International Terrestrial Reference Frame (ITRF) (Petit and Luzum 2010). Essential advantages of GNSS in the context of PM estimation are (1) continuous signal registration, (2) a globally distributed network of ground sites, and (3) a wide and stable constellation of satellites (Ray et al 2017). This concerns, in particular, the whole multi-GNSS constellation with almost 120 satellites in space, including GPS, GLONASS, Galileo, BeiDou, and QZSS at different altitudes and different revolution periods (Montenbruck et al 2017; Weiss et al 2017). In contrast to PM, the GNSS technique is not capable of delivering independent information about UT1 as it requires the ability to separate the axial rotation of the earth relative to the celestial frame and rotation of the satellite orbit nodes in the inertial frame (Senior et al 2010; Thaller et al 2007)
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