Performance Assessment of Galileo High Accuracy Service for PPP and Atmospheric Correction Impact in 2023

Since early 2023, the Galileo High Accuracy Service (HAS) has been officially providing free corrections for Precise Point Positioning (PPP). The HAS is structured into two service levels. The first level (SL1), currently available worldwide, delivers orbit and clock corrections along with code biases for three GPS frequencies (L1, L2C, L5) and four Galileo frequencies (E1, E5a, E5b, E6). The second level (SL2), which is planned to operate exclusively within the European Coverage Area (ECA), will include atmospheric corrections.

In January 2023, the Service Definition Document (SDD) established the targeted HAS accuracy at 15 centimeters horizontally and 20 centimeters vertically, with a confidence level of 68% for static users outside the Pacific region.

An initial evaluation of the HAS performance was conducted between Day of Year (DOY) 92 and DOY 153 of 2023. In terms of correction availability, the service supports an average of 16 to 21 corrected satellites (GPS and Galileo together), depending on the user’s location. Regarding accuracy, the corrections improved the Signal-In-Space Range Error (SISRE) by 54% for Galileo and 61% for GPS, when compared to broadcast ephemeris.

To validate the HAS corrections, Precise Point Positioning (PPP) was performed using data from 132 Regional Reference Frame Sub-Commission for Europe (EUREF) stations across Europe. The analysis was conducted in static mode with a dual-constellation configuration (GPS/Galileo), a 30-second sampling interval, float ambiguities, and uncombined measurements. The results achieved a 68% accuracy of 4.4 centimeters horizontally and 4.7 centimeters vertically.

These EUREF stations were subsequently employed to generate atmospheric corrections, specifically ionospheric and tropospheric, to test the second service level. Three station networks with varying densities were constructed, consisting of 132, 49, or 34 stations. After an evaluation of these atmospheric corrections coming from these networks, a PPP positioning over 64 other EUREF stations has been performed. This positioning was carried out in kinematic mode, using the same dual-constellation setup, 30-second sampling, float ambiguities, and uncombined measurements.

The results demonstrated that atmospheric corrections had a significant impact on positioning performance. The 68% accuracy improved by 43% horizontally and 47% vertically. Furthermore, the horizontal convergence time was reduced by half and is achieved in 60 minutes instead of 127 minutes. It highlights the potential benefits of the second service level for real-time applications.

ACKNOWLEDGEMENTS

 We would like to acknowledge Munich Aerospace for the scholarship that made this study possible.

REFERENCES

[1] EUSPA, “Galileo high accuracy service service definition document (HAS SDD),” European Union, Tech. Rep., 2022.