What is REFIMEVE?
The REFIMEVE Network: High-Performance Time and Frequency for everyone
The time used globally is based on the development of International Atomic Time (TAI). This TAI relies on complex processing of the scales produced in the National Metrology Institutes (NMIs) of various countries, with the SYRTE in France playing a key role. To achieve this, these NMIs develop atomic clocks that generate a reference frequency, which can achieve a precision of one second over the age of the Universe-13.8 billion years! This extraordinary precision led international metrology bodies to modify the definitions of the units of physical quantities (such as length, mass, temperature, etc.) in 2018, all of which are now tied to the second, the unit of time and frequency. As a result, the second has become the reference quantity for all measurements.
Having an accurate reference for time and frequency is thus imperative in activities where measurement plays a central role. The goal of T-REFIMEVE is to provide the scientific community and industry with a complete set of temporal signals at the highest international level that metrology laboratories can offer, leveraging the exceptional precision of atomic clocks. Using the optical fibers of the national telecommunications network RENATER, the time and frequency signals developed at SYRTE are transported to users. To maintain the initial precision, any disturbances during transmission must be corrected. This correction, achieved through optical and electronic methods, is so perfect that users connected to this network receive a signal of the same quality as if the clock had been relocated to their laboratory. This represents a remarkable pooling of resources, a technological breakthrough beyond GPS.
The T-REFIMEVE project amplifies what was achieved in the previous REFIMEVE+ project. By adding time signals for event synchronization, the potential number of users has greatly expanded. This includes synchrotrons like SOLEIL (https://www.synchrotron-soleil.fr/fr) and ESRF (https://www.esrf.fr/), which serve thousands of users. Numerous scientific fields will benefit from these new services: atomic and molecular spectroscopy, astrophysics, high-energy physics, and fundamental physics tests.
One emerging scientific domain, known as chronometric geodesy, will fully exploit the potential of this project. It relies on the fact that a clock delivers a frequency that depends (very slightly) on its altitude, an effect of general relativity. In 2016, it was shown that clocks connected via optical fiber over 1400 km between Paris and Braunschweig, Germany, deviated from each other by one second over 16 million years. This revealed a 20-meter altitude difference between the two clocks. Building on this principle and connecting French tide gauges in Brest, Marseille, and Dunkerque to the T-REFIMEVE network will allow us to monitor sea levels using the ultimate performance of atomic clocks and the fiber-optic network. The expected precision, down to the centimeter, which is unmatched by GPS, is exactly what is needed to track the rising sea levels due to climate change, which are projected to occur in the coming decades.
This is just one of the applications that this fiber-optic network with its time and frequency services will enable. Over 30 laboratories and institutes across the country will be connected, with additional laboratories nearby able to easily connect in the future. This situation is unparalleled worldwide.
