DEPARTMENT 1 : Reference systems and Geodynamics

Section 1 : Time, Earth rotation and Space geodesy

Project 1. Time and Time Transfer

One of the missions of the Royal Observatory of Belgium (ROB) is to integrate Belgium into international space and time reference systems through determination of Time, and precise positioning.
The ROB is therefore involved in the realization of the International Atomic Time (TAI), from which one gets UTC (Universal Time Coordinated) by adding the leap seconds, UTC being the basis of the legal time.
Four atomic clocks (3 cesium clocks and 1 Hydrogen Maser) of the ROB are presently used by the BIPM (Bureau International des Poids et Mesures) for the realization of TAI.

The research developed at the ROB in the Time domain concern GPS time transfer, i.e. remote clock comparisons based on the analysis of GPS signals. They aim at improving the precision in order to be able to compare the most precise atomic clocks in the world.

The ROB also provides for Belgium a realization of UTC, named UTC(ORB), which is therefore the most precise time (i.e. most closest to UTC) for Belgium.
This time scale is based on the signal of one of our active Hydrogen Maser CH1-75, of which the frequency is readjusted using in order to be stable with respect to UTC. UTC(ORB) is permanently monitored through its comparison with all the other laboratory clocks, and through its comparison with respect to other national time scales, using the GPS time transfer technique. The difference between UTC(ORB) and UTC stays always below 0.1 microsecond.
The time laboratory of the ROB distributes the exact time, i.e. UTC(ORB), through telephone line (which can be obtained with a PC and a modem), and via Internet (NTP).
The Royal Observatory is also in charge to inform the Belgian users about the leap seconds which are applied, if necessary (i.e. if the difference between UTC and the Earth rotation comes close to 0.9 sec), on June 30 and/or December 31 of the year considered.

Staff