Time and Frequency Monitoring and Control system is a complex and very articulated system allowing to check critical points and monitor all the Laboratory functionalities. The available monitoring tools, together with a new alert broadcasting system, allow the operators to be informed in case of problems, failures or anomalies and, hence, to be in the position to intervene in order to grant the best Laboratory efficiency.
Here, we show an interactive tool, among the ones that are normally employed for monitoring some of the Laboratory functionalities.
This tool allows to monitor the behavior of UTC(IT) time scale trough the satellite time synchronization systems, namely the GPS and the TWSTFT.
It’s composed by three sections, namely:
- Date and time: this section shows the current date and time, being the Date expressed in Gregorian and MJD (*) formats, while the Time is expressed in “local Time” (indicated as CEST, the “Central European Summer Time”), UTC and TAI. The integer number of seconds between UTC and TAI, indicated as “leap seconds” (in Italian “secondi intercalari”), is also shown.
(*)The Julian Day, is the number of days starting from midday of Monday January 1st 4713 b.C. according to the Julian calendar (November 24th 4714 b.C. according to the Gregorian calendar). It was proposed for the first time by Giuseppe Scaligero in 1583. The Julian days system was projected to give the astronomers a single dates system, without the difficulties of leap years and different calendars combination.
The Julian Date is the Julian Day combined with the fraction of day expired, starting from midday of Universal Time.
The Modified Julian Date (MJD) was introduced by the Smithsonian Astrophysical Observatory in 1958 to make measurements on the Sputnik orbit and it is defined in terms of Julian Date as follows: MJD = JD – 2400000,5. The 0,5 shift means a MJD starts and ends at midnight of the Universal Time, instead of midday. MJD 1 corresponds to November 18th 1858.
- GPS Coordinates: this section shows the coordinates of the GPS receivers antennas used for the remote comparison of Laboratory atomic clocks and time scales, expressed in the WGS 84 system. This is a standard for use in cartography, geodesy, and navigation. It comprises a standard coordinate system for the Earth, a standard spheroidal reference surface (the datum or reference ellipsoid) for raw altitude data, and a gravitational equipotential surface (the geoid) that defines the nominal sea level. The latest revision is WGS 84 (aka WGS 1984, EPSG:4326), established in 1984 and last revised in 2004. WGS 84 is the reference coordinate system used by the Global Positioning System.
- UTC(IT) time scale monitoring: this is the main section of the tool, allowing to compare the behavior of UTC(IT) time scale with respect to the time scales generated at main NMIs. This comparison is carried out by means of the two satellite synchronization techniques that are currently used for the remote comparison of atomic clocks and time scales, that is the GPS and the TWSTFT. Concerning the GPS, two type of estimates are considered, namely the classic “All in View” approach using “ionosphere free GPS measurements” (yielding to uA and uB type uncertainties of around 3 ns and 5 ns, respectively) and the geodetic methods (i.e. the “Precise Point Positioning”, GPS-PPP, and the “Orbit Determination and Time Syncronization”, GPS-ODTS) allowing to get uA and uB uncertainties at the level of 100 ps and 1 ns, respectively. GPS PPP and ODTS are algorithms developed in cooperation with the Geodetic Survey Division of the Natural Resources Canada (NRCan) and the Spanish aerospace company GMV. The mentioned satellite synchronization estimates covers a time span of one week, with associated latencies of 3 days for the GPS PPP, 1 day for the GPS AV, 2 hours for the TWSTFT and 30 minutes for the GPS ODTS. A further plot, shows the “official” behavior of UTC(IT) as estimated by BIPM, with respect to the UTC time scale, in both the “classical” and “rapid” version (UTC and UTCr).