The annual Asia Pacific Regional Geodetic Project (APRGP) GPS campaign is an activity of the Geodetic Reference Frame Working Group (WG) of the Regional Committee of United Nations Global Geospatial Information Management for Asia and the Pacific (UN-GGIM-AP). This document describes the data analysis of the APRGP GPS campaign undertaken between the 15th and 22nd of September 2019. Campaign GPS data collected at 101 sites in ten countries across the Asia Pacific region were processed using version 5.2 of the Bernese GNSS Software in a regional network together with selected IGS (International GNSS Service) sites. The GPS solution was constrained to the ITRF2014 reference frame by adopting IGS14 coordinates on selected IGS reference sites and using the final IGS earth orientation parameters and satellite ephemerides products. The average of the root mean square repeatability of the station coordinates for the campaign was 1.8 mm, 1.6 mm and 5.4 mm in north, east and up components of station position respectively.

<div>Within the preparation for the release of the International Terrestrial Reference Frame 2020, the International GNSS Service (IGS) analysis centers (ACs) issued the results of the third reprocessing campaign (IGS Repro 3) of all the GNSS network solutions backwards starting from 1994. For the first time, the IGS reprocessing products include not just GPS and GLONASS, but also the Galileo constellation. In this study, we show the methodology and results of the orbit combination provided by the IGS Analysis Center Coordinator (IGS ACC) at Geoscience Australia. The quality of the provided combined orbit products was cross-checked with the individual IGS Repro3 AC contributions. The internal consistency of the individual AC solutions with the combined orbits was assessed based on the root mean square of the 3D orbit differences. In 2020, the mean consistency of the combination is at the level of 9, 23, and 15 mm for GPS, GLONASS, and Galileo, respectively. The external validation was performed using Satellite Laser Ranging (SLR) observations. We proposed a novel approach to handling detector-specific biases in the results of SLR validation, reducing the standard deviation of SLR residuals by up to 15% for Galileo FOC satellites. The method is based on bias referencing to single-photon SLR stations that are not affected by the retroreflector signature effect. The proposed approach increased the internal consistency of the SLR dataset, facilitating the detection of orbit modeling issues. The standard deviation of SLR residuals of the best individual solution versus the combined equals 13/14, 15/16, 17/16, 16/16 mm for Galileo-FOC, -IOV, GLONASS-K1B, -M, respectively. Therefore, the combined solution can be considered equal or slightly better in quality compared to the best individual AC solutions. Searching for patterns in SLR residuals for different satellite-Sun-Earth geometries reveals that some issues in orbit modeling are not fully diminished for individual ACs. Eventually, we proved that the delivered combined orbit product may be considered the best solution overall. The combined solution benefits from the best individual solutions for each satellite type.</div> <b> Citation:</b> Zajdel, R., Masoumi, S., Sośnica, K. et al. Combination and SLR validation of IGS Repro3 orbits for ITRF2020. J Geod 97, 87 (2023). https://doi.org/10.1007/s00190-023-01777-3

<div>In the third reprocessing campaign (repro3) initiated by the International GNSS Service (IGS), 11 analysis centers (ACs) reanalyzed GPS/GLONASS/Galileo observations spanning 1994–2020 for station coordinates, satellite orbits, clocks, biases and attitudes. To improve the robustness of satellite products, the IGS AC Coordinator (ACC) carried out the satellite orbit combination, and the reference satellite attitudes were computed by the Technical University of Graz (TUG). The clock/bias combination was performed by Wuhan University via the IGS “Precise Point Positioning with Ambiguity Resolution” (PPP-AR) Pilot Project using the PRIDE <i>ckcom</i> software. This article aims at reporting the clock/bias combination results in the repro3. In particular, the consistencies for the combined GPS P1–P2/Galileo C1–C5 differential code biases (DCBs) and the GPS/Galileo uncalibrated phase delays (UPDs) among contributing ACs are all better than 0.1&nbsp;ns and 0.05 cycles, respectively. As a result, the consistencies for the combined GPS/Galileo satellite clocks/biases are better than 10&nbsp;ps, equating about 3&nbsp;mm which is very close to the nominal precision of carrier-phase. In general, the Hadamard deviation and PPP-AR results confirm the higher robustness of the combined satellite clock/bias products over their original AC-specific counterparts. This is because the combined satellite clock/bias products harvest the merits of AC-specific contributions by identifying and excluding outlier solutions from the combination process.</div> <b>Citation:</b> Geng, J., Yan, Z., Wen, Q. et al. Integrated satellite clock and code/phase bias combination in the third IGS reprocessing campaign. <i>GPS Solut </i>28, 150 (2024). https://doi.org/10.1007/s10291-024-01693-9