ADeLA2002 - Astrometry in Latin America ADeLA Publications Series, No. 1, 2003 R.Teixeira, N.V.Leister, V.A.F.Martin, and P.Benevides-Soares, eds. The Observatorio Naval Buenos Aires time service M.S. De Biasi1,2,J.Osorio1,2, J. Amenna1,2, C. Esper´on1,E.F.Arias3 1 Observatorio Naval Buenos Aires, Av. Espa˜na 2099,1107 Buenos Aires, Argentina 2 Facultad de Ciencias Astron´omicas y Geof´ısicas UNLP, Paseo del Bosque s/n, 1900 La Plata, Argentina 3 Bureau International des Poids et Mesures, Pavillon de Breteuil, 92312 S`evres Cedex, France Abstract. The time service at the Observatorio Naval Buenos Aires (ONBA) maintains local UTC scale which is the basis of the legal Ar- gentine time scale. It is one of the three laboratories in South Amer- ica that participates in international time links, by GPS multi-channel common-views between the ONBA and the United States Naval Obser- vatory (USNO). We describe the ONBA equipment and activities. 1. Historical background The ONBA was created in 1881 to provide time to the ships that were at the port of Buenos Aires. Since 1923 this department of the Argentine Navy has been charged to maintain and disseminate the Argentine legal time. The first equipment of the time service at the ONBA included three electric pendulums, in 1937 the first speaking clock of French fabrication acquired by the Navy was installed, and in 1938 the first oscilloquartz. The first atomic clock was installed in 1967. From 1940 to 1981 the ONBA contributed with astrometric observations to the international time and latitude services. At present, the time service at the ONBA maintains UTC(ONBA) which is the basis of the Argentine legal time. This local realization of UTC is dis- seminated by time signals; the legal time is distributed to all the country by telephone line and radio-broadcast time signals. The ONBA is also a member of the National Council of Communications. 2. Time Service The time service at the ONBA is equipped by two industrial caesium clocks, a microphase-stepper, a GPS receiver Truetime XL-DC and a recently incor- porated a GPS single-frequency multi-channel receiver TTS-2 developed by the Polish Academy of Sciences. The source of UTC(ONBA) is a HP5061A clock and a microphase-stepper. 23 24 de Biasi, Osorio, Amenna et al. For clock comparison, until the end of 2000 both caesium clocks were contin- uously compared with the industrial caesium clocks of the time service at the In- stituto Geogr´afico Militar Argentino (IGMA) by TV link, being the IMGA time service charged to submit clock comparison data to the BIPM as UTC(IGMA)- UTC(ONBA). As the common-view methods of GPS time transfer is one of the most precise and accurate methods for time comparison between clocks, the sit- uation changed since the GPS receiver TTS-2 has been acquired. Multichannel receivers permit the observation of several satellites simultaneously and relate one pulse per second (1pps) signal of the local clock to the 1pps pulse of the receiver operating in GPS synchronisation mode. The time service at the ONBA is one of the three time laboratories in South America that submits data to the BIPM and keeps the local representation of UTC as UTC(ONBA). Figure 1 shows the traceability of UTC(ONBA) to UTC, which is monthly provided by BIPM Circular T, from January 1st 1998 until the end of Jan- uary 2003. The difference UTC-UTC(ONBA) takes from 0.5 to 1 microsecond in the period january-september 1998, corresponding to the installation of two HP5061A coming from Omega station at Trelew, Argentina, and the single- channel GPS Truetime. After this period the difference decreases to 200nsec. From June 2001 the clock comparison is done by GPS multi-channel common views and ONBA participate in international time links. Until the end of September 2002 the difference is at the level of 300nsec and gradually increases up to 600nsec, it shows that a clock update is necessary. Actually, there are few time laboratories in the southern hemisphere equipped with the most accurate time transfer systems that submit data to BIPM. In South America we can find ONBA, IGMA and Observatorio Nacional de Rio de Janeiro (ONRJ), Brasil. Another Latin-American time laboratories are: Cen- tro Nacional de Metrolog´ıa (CNM), El Marqu´es, M´exico, and Real Instituto y Observatorio de la Armada (ROA), San Fernando, Espana˜ IGMA, ONRJ, ROA and CNM participates in TAI, as given in sections 8a and 9a Annual Report BIPM 2001. 3. Time dissemination Some legal aspects are included in the dissemination of UTC as national time keeping. UTC(ONBA) is kept in close agreement with UTC and follows ITU- R recommendations for the time dissemination in Argentina, as ONBA is the authority responsible for time dissemination in the country. UTC(ONBA) is disseminated by: – LOL station (Buenos Aires, Argentina) broadcasts time signals and stan- dard frequencies at 5, 10 and 15 MHz (discontinued for maintenance) in five one-hour interval per day. One interval of transmission contains second pulses of 5 cycles of 1000 Hz modulation, announcements of hours and minutes every 5 minutes, followed by 3 minutes of 1000 Hz or 440 Hz modulation. DUT1 is transmitted accordingly to the ITU-R recommendations. – speaking clock with an access phone number only accessible in Argentina – hourly and half hourly radio-broadcast time signal The Observatorio Naval Buenos... 25 Figure 1. The traceability of UTC(ONBA) to UTC. – since December 2002 internet time service at web site www.hidro.gov.ar/hora/hora.asp Another time signals in Latin America are YVTO from Direcci´on de Hidro- graf´ıa y Navegaci´on, Observatorio Cagigal, Venezuela; EBC from ROA and CBV Playa Ancha Radio from Servicio Hidrograf´ıco Oceanogr´afico de la Armada de Chile, and another time services are CNM, ONRJ and ROA. 4. Conclusion The Time Service at ONBA keeps the local representation of UTC, UTC(ONBA) which is the basis of the Argentine legal time. The equipment of this time laboratory has been partially updated in the last years. ONBA submits data form GPS multi-channel common-views with USNO to BIPM. The traceability of UTC(ONBA) to UTC is shown. The Time Service at ONBA complies well with the requirements of national time keeping, but a clock update should be necessary to contribute with clock data to TAI. References Annual Report of BIPM Time Section 2001 26 de Biasi, Osorio, Amenna et al. TTS-2 Time Transfer System-2, Nawrocki J. Polish Academy of Sciences, Jan- uary 2000 Discussion Andrei: Did you have any propose to implement the time stamping service? De Biasi: Yes, the Naval Observatory of Buenos Aires is working in the subject jointly with other state organisms. M´endez: Nice talk! Could you provide with a web address to get time stamps through the Internet for Latin-American users? Thanks. De Biasi: Sorry that I don’t remember exactly a web address, but you can find them in the Annual Report of the Bureau International des Poids et Mesures (BIPM). Anyway, a laboratory K that contributes must provide time needed for time stamps to BIPM, following ITU and CCTF recommendations. I mean, this ”hour” must be UTC(K). Beliz´on: Do you have a calibration service like a national patron of time and frequency? De Biasi: Affirmative..