SPMS is a long-term project, the aim of which was to support the monitoring of the effectiveness of the EGNOS (European Geostationary Navigation Overlay Service), the European SBAS (Satellite Based Augmentation System). It was implemented in short-term grants, which allowed for adjusting the EUSPA (European Union Agency for the Space Programme) requirements to changing conditions and modernization of the system. Thanks to the establishment of a wide consortium of European companies and scientific units that constantly monitor the EGNOS service, it was possible to independently analyse the distributed corrections and the quality of the service’s operation.

Many aspects related to the use of the service and parameters reflecting its reliability and accuracy were monitored and analysed. CBK PAN was involved in two tasks, the first of which included monitoring the availability of EGNOS corrections and the accuracy of determining the local position based on EGNOS corrections from the signal received directly from a geostationary satellite. As part of the second task, the positioning accuracy using EGNOS corrections downloaded via the Internet from the EDAS (EGNOS Data Access Service) service was tested, and in addition, the results obtained were compared with the results obtained in the first task.

The research was based on data from the ASTRA-5b (PRN123) satellite located above the equator at longitude 31.5°E. The signal at the L1 frequency was received and recorded by three receivers located on the roof of the CBK PAN building in Warsaw, working in the interval of 1 s and observing all GPS satellites from 0° elevation above the horizon.

As part of the first task, the Trimble NetR9 multi-system receiver operating at the CBKA station collected observational data for the analysis performed by the CNES (Centre National d’Études Spatiales), as well as corrections of the SBAS system, used to control the calculations performed by the second receiver. It was a Septentrio PolaRx2 working on a CSIS station, equipped with the option to work with the SBAS corrections. This receiver determined its position for each observation epoch using GPS observations and EGNOS correction.

The second task involved monitoring the accuracy of determining the local position for the EGNOS correction signal received via the Internet from the EDAS service. The Septentrio PolaRx2 receiver at the CNET station determined its position based on GPS observations and EGNOS corrections (as did the receiver at the CSIS station). Both Septentrio devices were connected to one antenna.

As the purpose of both tasks, at the end of each day, calculations were performed, the result of which were plots presenting the analysed parameters, independently for CSIS and CNET stations. These data were made available to units cooperating in the project. These include:

• values of precision level of determined horizontal position HPL (horizontal precision level) and vertical position VPL (vertical precision level) in UTC time;
• distributions of HPE (horizontal position errors) and vertical VPE (vertical position errors) in relation to CSIS station coordinates determined by geodetic methods;
• Stanford diagrams for the precision level of determined horizontal and vertical position;
• differences between the coordinates determined by the receiver working with the usage of EGNOS SIS corrections for each observation epoch and the reference coordinates of the station.

Moreover, after the end of each quarter, reports were prepared for both stations – CSIS and CNET, including monthly analyses of the availability of GPS observations and EGNOS corrections, quarterly plots of the HPE horizontal and VPE position error distribution values determined for 95% of the observed values, as well as quarterly plots of differences from the reference position in horizontal and vertical components.

The results of the analyses were the basis for improving the EGNOS system and supplementing correction deficiencies, performed at the request of the GSA by the system operator.