G. Galluzzo, P. Waller, J. Hahn, C. Plantard, D. Ibañez, S. Circiu, European Space Agency, The Netherlands; C. García, F.J. Sobrero, D. Jiménez, E. López, A. Lobit, D. Del Valle, GMV Spain

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Abstract:

This paper provides an overview of the activities conducted at the European Space Research and Technology Centre in the domain of GNSS timescales monitoring and assessment, and the related multi-GNSS receivers calibration methodology required to enable this evaluation. The European Space Agency (ESA), as the Galileo System Design Authority (SDA), is responsible for the development and qualification of new Galileo system releases (known as System Builds), and is also contributing, along other Programme stakeholders, to the continuous monitoring of the system navigation and timing performance. A number of tools and resources are being used to fulfil these objectives and to generate performance figures of merit in near real time. This is particularly important to support the prompt diagnose and resolution of potential system anomalies, that might propagate to the timing users community. The Time and Geodetic Validation Facility (TGVF-X), with its core infrastructure hosted and operated at ESTEC, is the main system validation and prototyping testbed currently being used by ESA. TGVF-X is a culmination of a project that dates back to the early 2000s, to the early inception of the Galileo project, encompassing the early experimentations of the Galileo System Time (GST) and of Galileo on-board atomic clocks. The first part of this paper will address a number of timing performance figures of merit generated by TGVF-X, including GNSSs on-board clock stability and UTC timing dissemination accuracy, not only limited to the case of the Galileo system. Results from GPS, GLONASS and Beidou systems will also be presented. The methodology for the UTC time dissemination and GNSS to GNSS Time Offset accuracy will be presented and results from different GNSSs will show that a UTC time dissemination accuracy below 5ns (95%) can be achieved. The second part of this paper will introduce the multi-GNSS receiver calibration activities that are required for the monitoring of GNSS timescales. As reported earlier (e.g. [1, 2]), we have developed and validated methods for the absolute calibration of GNSS receiver chains, including the antenna. Those methods have now been extended to cover all GPS, Galileo, Glonass and Beidou-2 and -3 signals, allowing for a comprehensive and consistent calibration process. Two receivers have been fully calibrated and are operating in our Laboratory. They are connected to UTC(ESTC), our local realisation of UTC, which is used as reference for the monitoring of the GNSS timescales. ESA, as member of the United Nations International Committee on GNSS (ICG), is also contributing to the harmonisation and standardisation of GNSS performance metrics, and also contributing to GNSS timing interoperability discussions. A brief status of these activities will be outlined in this paper. [1]: “Absolute calibration of GNSS timing stations and its applicability to real signals”, E.Garbin et al., Metrologia 56 015010, 2019 [2]: Cross-calibration of multi-GNSS Receiver Chains, P.Waller et al, Joint IFCS-EFTF, Orlando, 2019