Mitigation of multipath effects in multi-GNSS and multi-frequency precise point positioning with multipath hemispherical maps

To mitigate multipath effects in multi-GNSS and multi-frequency precise point positioning (PPP), we constructed multi-GNSS and multi-frequency multipath models using the multipath hemispherical map (MHM) method. We investigated multi-GNSS and multi-frequency multipath effects by analyzing the impact of multipath corrections on observation residuals and PPP performance. In general, greater code rates and signal strengths lead to smaller observation residuals and multipath corrections, and signals with better anti-multipath performance are obtained. Notably, the observation residuals and multipath corrections of the GPS L5 signals are the smallest among those of the triple-frequency signals, and those of the GLONASS G1 signals are smaller than those of the G2 signals. Among the Galileo five-frequency signals, those of the E1 and E5 signals are the largest and smallest, respectively. Among the BDS-3 five-frequency signals, those of the B1I and B1C signals are greater than those of the other signals. Additionally, overlapping frequency signals with the same code rates and similar signal strengths display similar observation residuals and multipath corrections. In particular, the BDS-3 B1C signal has large phase residuals in the high-elevation region, possibly due to inaccurate receiver antenna phase center corrections applied. Surprisingly, the MHM method works well on it, possibly because the phase multipath corrections include elevation-specific errors. After multipath correction, the low-frequency multipath errors of multi-GNSS and multi-frequency observations are efficiently mitigated, significantly reducing the observation residuals and improving the observation accuracy. As a result, the three-dimensional convergence time of multi-GNSS and multi-frequency float kinematic PPP is reduced by 24.1%, with a 13.8% improvement in the positioning accuracy.