• Andreas Bauch - Head, Time Dissemination Working Group, Physikalisch-Technische Bundesanstalt

Reliable information about time-of-day, reliable access to accurate instant of time and of fre-quency have become an essential necessity in modern societies’ critical infrastructure. The needs of different sectors of society are very expansive, spanning several orders of magnitude in terms of accuracy. They are also quite diverse in terms of trustworthiness and the need to demonstrate traceability of local measurements being made to national or international standards and to have access to legal time. The availability of GNSS signals represents an asset that should be optimally used, and indeed their usage is abundant in many application fields. It has been stressed on sev-eral occasions that the direct reception of GNSS signals should be accompanied by other measures to guarantee the required metrological and legal traceability, but also to improve assuredness of the availability.

In view of the diversity of needs and regulations, three different services have been proposed and discussed discussed in the framework of the EGALITE project (Galileo Timing Service Ex-tension and Consolidation) which had been launched in September 2018 and received funding by the European Commission as part of the Horizon 2020 framework programme:

• A dedicated timing integrity service that relies on a network of world-wide timing moni-toring stations.
• A GNSS common-view evaluation service provided by an external partner, but relying on the availability of respective data from national metrology institutes4.
• A service provided by a National Metrology Institute which monitors GNSS signals and publishes results and possibly alerts in open access3. The example of the service offered by Physikalisch-Technische Bundesanstalt (PTB) is going to be presented.

The two latter services were designed in view of the competence of individual states to define and impose the use of legal time for certain applications. All proposed services have in common that the primary physical source of time information should be backed by at least one secondary source.