Analysis and Comparison of Sub-daily Polar Motion Derived from BDS, GPS, GLONASS and Galileo

Earth Rotation Parameters (ERPs), including polar motion (PM) and length of day, are crucial for describing the motion of the Earth's axis of rotation and linking the terrestrial and celestial reference system. ERPs can be categorized into long-term components and sub-daily components with periods shorter than two days. For the sub-daily ones, they reveal the impact of ocean tides, atmospheric tides, and other factors on Earth's rotation over short timescales, providing valuable insights into the dynamic process of Earth's motion. Compared to other techniques such as Satellite Laser Ranging, Very Long Baseline Interferometry, and Doppler Orbitography and Radiopositioning Integrated by Satellite, Global Navigation Satellite System (GNSS) technique offers advantages such as a densely distributed global station network, low equipment costs, continuous data tracking and high data sampling rate, making it particularly suitable for studying sub-daily PMs.

Since 2020, the Beidou Satellite Navigation System (BDS) has been officially completed and put into operation. Comparing with GPS, GLONASS, and Galileo, BDS has hybrid constellations with MEO and IGSO satellites which could bring new features into the derived sub-daily PMs. Therefore, this study first focuses on the precision of sub-daily PMs derived from BDS only. All the sub-daily PMs is based on 3-arc-length solutions with a 1-h temporal resolution. The results show that, compared to MEO-only, the addition of IGSO can reduce PMX from 183 to 161μas. For PMY, the addition of IGSO shows a similar improvement, reducing it by approximately 10%. Secondly, we transforme the time series of sub-daily PMs from different systems into the frequency domain by Fast Fourier transform (FFT) to identify and analyze those tidal and non-tidal signals. The results of spectral analysis indicate that the more diverse constellation configuration can effectively reduce the impact of spurious signals especially nearby 28-h term. In addition, more detailed comparisons and analyses with respect to the PMs derived from GPS, GLONASS, and Galileo are also presented. Furthermore, we also analyze the impact of weighting scheme in multi-GNSS combined solutions. Properly adjusting the weights of BDS can effectively improve the accuracy of sub-daily PMs. Finally, we assessed the GNSS-based empirical models with three priori empirical models, IERS2010 model, Gipson model and Desai-Sibois model. Multi-GNSS model with different constellation configurations shows the best consistency with the priori model.