GNSS-specific characteristic signals in power spectra of multi-GNSS coordinate time series

Understanding satellite system-specific artifacts and geophysical phenomena affecting coordinate estimates using multi-Global Navigation Satellite System (GNSS) data is of vital importance to ensure the accuracy and reliability of positioning, enabling scientific research to yield trustworthy and informed results. Therefore, this study is conducted to investigate the precision of single/multisystem solutions, factors affecting these precisions due to spurious periodic signals, and the mitigation of these signal powers in the frequency domain after fusing multi-GNSS data. For this purpose, the multi-GNSS data from 46 globally distributed International GNSS Service (IGS) stations spanning from January 1st, 2020 to August 31st, 2022, were processed using PRIDE-PPPAR v2.2 software in Precise Point Positioning (PPP) mode for GPS-, GLONASS-, Galileo-, and BeiDou-only solutions, as well as all possible combinations with GPS. The coordinates in the time domain were then converted into the frequency domain utilizing the Lomb-Scargle algorithm. The results of this experiment indicated that the GPS-only solutions have the best coordinate precision among the other satellite systems. The GLONASS, Galileo, and BeiDou systems exhibit orbital resonance up to the 3rd, 4th, and 3rd harmonics, respectively, whereas the GPS system, with a half of a sidereal day orbital period, exhibits no resonant effects due to the Nyquist frequency in the daily sampled time series. Enhanced coordinate precision for the multi-GNSS solutions was achieved with the GPS + GLONASS + Galileo + BeiDou combination (with only 0.1 mm deterioration in the east component), as well as the GPS + GLONASS + Galileo and GPS + Galileo combinations. The power spectra, particularly for the quadruple multi-GNSS combination, revealed that the system-specific periodic signals for GLONASS, Galileo, and BeiDou lost, on average, 85%, 55%, and 75% of their power in all components, respectively. Omitting the BeiDou and GLONASS systems from the quadruple and triple combinations slightly altered the power reductions of the Galileo systems. In other words, power reductions for orbital artifacts decreased as the number of satellite systems in the combination decreased. Interestingly, omitting specific systems did not significantly affect the fortnightly signals in multi-GNSS solutions. (c) 2024 COSPAR. Published by Elsevier B.V. All rights reserved.