Recommendation 4 of the 19th CCTF (2012)

Concerning the upgrade and calibration of global navigation satellite systems (GNSS) equipment in the timing laboratories contributing to Coordinated Universal Time (UTC) towards multi-frequency, multi-constellation receiving systems

The Consultative Committee for Time and Frequency (CCTF),

considering that

• atomic frequency standards have achieved unprecedented stability and accuracy, and that further advances in this field are under way,
• the ability to compare these standards for the realization of UTC is dependent on the accuracy and precision of time transfer methods based on GNSS,
• data from Global Positioning System (GPS) satellites plays an important role in time and frequency transfer,
• the GLONASS constellation is now complete and a modernization of the GLONASS system is under way,
• deployment of the European Galileo constellation started in 2011 and should be completed in the coming years,
• the People’s Republic of China has started launching BeiDou/COMPASS satellites for regional applications, and the global constellation will be operational in the coming years,
• present uncertainties in the calibration of equipment at timing laboratories currently have a significant impact on international time transfer in general and on the accuracy of the computation of UTC in particular,
• GPS time transfer based on dual-frequency code and carrier-phase data is used in the operational computation of UTC for some time links,

noting that

• the costs associated with equipment acquisition, installation, operation, and maintenance are less than the purchase price of a single caesium frequency standard,
• many software algorithms using dual-frequency code and carrier-phase data are either available or under active development,
• some of these algorithms already allow for the combination of GPS and GLONASS data,

recommends that

• the laboratories contributing to UTC upgrade their equipment towards multi-frequency, multi-constellation receiving systems providing code- and carrier-phase measurements,
• institutions developing software algorithms for time transfer work to upgrade their multi-constellation and multi-receiver solutions,
• the BIPM in collaboration with the regional metrology organizations (RMOs) develops calibration guidelines for new multi-frequency, multi-constellation equipment,
• the BIPM continues to organize and run campaigns to measure delays of this new GNSS equipment in laboratories, with the support of the RMOs within the frame of regional comparisons,
• all laboratories, especially those playing a unique role in International Atomic Time (TAI) computations, such as pivot laboratories and those contributing directly to Section 5 of the BIPM Circular T, to supply data from at least three GNSS receivers traceable to their local realization of UTC; this would help verify the stability of their hardware delays.

DOI : 10.59161/CCTF2012REC4E