Reporter 419, 27 April 1998

Engineering team helps to synchronise watches all over the world

Across the world people are preparing for Millennium celebrations while a team of electrical engineers at the University are working to make international time as accurate as possible.

The project to synchronise time measurements by satellite could make plane travel safer, says Professor Peter Daly, head of the Institute of Satellite Navigation in the School of Electronic and Electrical Engineering.

The University is currently participating in the first international effort to co-ordinate international time transfer via the Russian navigation satellite system, GLONASS. Since January, measurements synchronised to satellite time have been made at laboratories in Holland, Germany, China, Leeds and Russia and the project will run for many years to come. The University has one of the best-equipped laboratories in the UK for this research.

The schedule of measurements is prepared by the Bureau International des Poids et Mesures, the body responsible for co-ordinating international time and frequency, which uses information from laboratories around the world to gradually align timing standards.

The project will have important consequences. “When you’re landing a plane the more accurate your timing is the more accurately you can position yourself. Would you rather land within one metre of the runway or 100 metres?” says Professor Daly.

Safety could be improved in all phases of flight. “The plane needs to tell other planes near it just how close they are – and this will become more important as the skies get more and more crowded. If you know where you are and what time it is you can judge how to avoid other planes – it all goes back to timing standards.” It could be well into the next century before these systems are in operation in the skies, but aviation experts have made some trials and the results are encouraging.

The combined international effort is designed to lead to higher accuracy in the definition of international time itself. The international definition of a second is based on highly regular ‘clock ticks’ from atomic clocks and by transmitting information between them via satellite the project will discover how accurate international time is. “International time is already pretty accurate, to the order of tens of nano-seconds,” says Professor Daly.

People have been trying to co-ordinate international time for decades, and the advent of satellites has helped enormously. “Before satellites existed the only way to compare clocks in France and Germany would be to get them in the same place,” says Professor Peter Daly. “It was very difficult to know how accurate the comparison was as you wouldn’t know if the clock had changed along the journey. Now time can be relayed via satellite.”

The project runs in parallel with a similar programme to transfer time via the Navstar Global Positioning System (GPS). The University has participated in this programme since 1990. The Leeds contribution is unique as its sensor/ receiver can handle GPS and GLONASS simultaneously, allowing direct comparisons of the US and Russian atomic clocks controlling the two satellite systems.* More...

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