Two methods to determine scale-independent GPS PCOs and GNSS-based terrestrial scale: comparison and cross-check

Abstract

The GPS satellite transmitter antenna phase center offsets (PCOs) can be estimated in a global adjustment by constraining the ground station coordinates to the current International Terrestrial Reference Frame (ITRF). Therefore, the derived PCO values rest on the terrestrial scale parameter of the frame. Consequently, the PCO values transfer this scale to any subsequent GNSS solution. A method to derive scale-independent PCOs without introducing the terrestrial scale of the frame is the prerequisite to derive an independent GNSS scale factor that can contribute to the datum definition of the next ITRF realization. By fixing the Galileo satellite transmitter antenna PCOs to the ground calibrated values from the released metadata, the GPS satellite PCOs in the z-direction (z-PCO) and a GNSS-based terrestrial scale parameter can be determined in GPS + Galileo processing. An alternative method is based on the gravitational constraint on low earth orbiters (LEOs) in the integrated processing of GPS and LEOs. We determine the GPS z-PCO and the GNSS-based scale using both methods by including the current constellation of Galileo and the three LEOs of the Swarm mission. For the first time, direct comparison and cross-check of the two methods are performed. They provide mean GPS z-PCO corrections of $$- 186 \pm 25$$ - 186 ± 25 mm and $$- 221 \pm 37$$ - 221 ± 37 mm with respect to the IGS values and $$+ 1.55 \pm 0.22$$ + 1.55 ± 0.22 ppb (parts per billion) and $$+ 1.72 \pm 0.31$$ + 1.72 ± 0.31 in the terrestrial scale with respect to the IGS14 reference frame. The results of both methods agree with each other with only small differences. Due to the larger number of Galileo observations, the Galileo-PCO-fixed method leads to more precise and stable results. In the joint processing of GPS + Galileo + Swarm in which both methods are applied, the constraint on Galileo dominates the results. We discuss and analyze how fixing either the Galileo transmitter antenna z-PCO or the Swarm receiver antenna z-PCO in the combined GPS + Galileo + Swarm processing propagates to the respective freely estimated z-PCO of Swarm and Galileo.

Sentinel-6A precise orbit determination using a combined GPS/Galileo receiver

“…In total, 30 such events were encountered in the 6-month data arc with an increased number of events found between end of December 2020 and mid-January 2021 as well as the second half of March 2021. All such phase slips occurred in the vicinity of the South Atlantic Anomaly (SAA), where the inner Van Allen radiation belt comes close to the surface of the Earth (Hess 1968). They may thus be interpreted as radiationinduced single-event effects (SEEs) in the receiver frontend, even though the detailed mechanism of their occurrence still needs further investigation.…”

“…GPS satellite orbits and transmit antenna data for the period of interest are aligned to the IGS14b reference frame and provide consistent kinematic positions of the receiver antenna phase center in this frame. In case of Galileo, possible frame height inconsistencies of 6-7 mm may arise from the use of manufacturer-calibrated transmit antenna patterns in the generation of Galileo orbit and clock products (Villiger et al 2020;Huang et al 2021) but would only explain potential discrepancies in the relative location of the GPS L1/L2 and Galileo E1/E5a PCOs. However, these amount to 16 mm and 18 mm for chamber and inflight calibrations (Table 3), respectively, and are thus consistent within 2 mm.…”

Precise orbit determination for BDS satellites

“…Hence, more efforts should be made to bridge the gap to obtain a consistent scale determined by different GNSS constellations. One of the possible ways is to use the onboard BDS, Galileo, and GPS data from LEO satellites, as done by Huang et al (2021).…”

GENESIS: co-location of geodetic techniques in space

“…A totally independent method to estimate scale-free GNSS PCOs is given via the usage of space-based GNSS observations and the gravitational constraints from the orbital dynamics of the corresponding low Earth orbiter (Huang et al 2022). The high consistency between the LEO-based and the Galileo-based approaches has been shown by Huang et al (2021). Despite the larger constellation of Galileo than that of LEOs (24 versus 10+ in 2022), the LEO-based approach has advantages in several important aspects.…”