- International Earth Rotation Service (IERS) Service International de la Rotation Terrestre Chairman of the Directing Board (1995-1999) C. Reigber The International Earth Rotation Service (IERS) was established in 1987 by IAU and IUGG and it started operation on 1988 January 1st. It replaces the International Polar Motion Service (IPMS) and the earth-rotation section of the Bureau International de l'Heure (BIH) ; the activities of BIH on time are continued at Bureau International des Poids et Mesures (BIPM). IERS is a member of the Federation of Astronomical and Geophysical Data Analysis Services (FAGS). I- Functions IERS is responsible for : - defining and maintaining the international terrestrial reference system recommended by the IUGG, based on observing stations that use the high-precision techniques in space geodesy; - defining and maintaining the international celestial reference system recommended by the IAU that is based on extragalactic radio sources, and relating it to other celestial reference systems; - determining the earth orientation parameters connecting these systems, the terrestrial and celestial coordinates of the pole and universal time; - organising operational activities for observation and data analysis, collecting and archiving appropriate data and results, and disseminating the results to meet the needs of users. In 1996 it relies on five observing techniques: Very Long Baseline Interferometry (VLBI), Lunar Laser Ranging (LLR), Global Positioning System (GPS), Satellite Laser Ranging (SLR), and Doppler Orbit Radiopo-sitioning Integrated on Satellite (DORIS). II- Organisation The main centres in IERS are the Central Bureau, Sub-bureaus, and Coordinating Centres for each of the observing techniques. It is supported by many other organisations that contribute to the tasks of observation and data processing. The Coordinating Centres are responsible for organizing observations, objects to be observed, schedules, preprocessing of observational results, etc. and for the selection of models and procedures to be used in the analysis of observations. These centres are the following in 1995. VLBI Coordinating Centre, until 1996 A new centre will be selected in 1996 NOAA, N/OES13 SSMC IV, Sta. 82 11 1305 East-West Highway Silver Spring, MD 20910 USA Internet: bcarter@ray.grdl.noaa.gov LLR Coordinating Centre OCA/CERGA Avenue Nicolas Copernic 06130 Grasse France Internet: veillet @ocar01.obs-azur.fr GPS Coordinating Centre Jet Propulsion Laboratory MS 238-540 4800 Oak Grove Drive Pasadena, CA 91109 USA Internet:BILL_MELBOURNE. JPL#u#330#u#QMail@JPL-335- SERVER.JPL.NASA.GOV SLR Coordinating Centre Center for Space Research 60605 The University of Texas at Austin Austin, TX 78712-1085 U S A Internet: schutz@utcsr.ae.utexas.edu DORIS Coordinating Centre Institut Geographique National B P 68 2 avenue Pasteur 94160 Saint-Mande France Internet: willis@ign.fr The observations are organized in networks for each of the observing techniques, under the responsibility of the IERS Technique Coordinating Centres. They are archived in data centres and distributed to Analysis Centres. Some of the centres contribute, in operational mode, earth-orientation data to the Sub-Bureau for Rapid Service and Predictions (weekly bulletins) and to the Central Bureau (monthly bulletins). Most Analysis Centres produce global solutions based on many years of observations, including the determination of station positions and velocities, earth rotation and, in the case of VLBI, directions of extragalactic compact radio sources. The Central Bureau combines the various types of results to obtain the final results, which are disseminated to the user community in Annual Reports and electronically accessed data bases. Assesment of the accuracy and precision of the contributed solutions is also provided. Technical Notes are distributed; some describe the IERS Standards, while others contain the reports of the Analysis Centres and details of the final IERS results. The mailing list includes 780 institutes in 62 countries: space-geodesy and astronomical observa-tories, geodetic institutes, universities, time services, etc. The observational results of VLBI, LLR, GPS, SLR and DORIS are archived at several centres, subject to the agreement of the relevant Coordinating Centres. The results on earth rotation and reference frames are archived at the network and analysis centres which obtained them, as well as at the Central Bureau. The atmospheric data related to earth-orientation variations from four major meteorological centres are collected, validated and made available by the Sub-Bureau for Atmospheric Angular Momentum. Currently, there are four participating centers contributing to the Sub-Bureau. It serves as a focal point for the collection of atmospheric measurements. The data is made available within the IERS and to the users community. Research is performed in order to assess the accuracy and completeness of the series derived by the participating meteorological centers. The Central Bureau decides and disseminates the announcements of leap seconds in UTC and values of DUT1 to be transmitted with time signals. The principal IERS centres are: CENTRAL BUREAU Observatoire de Paris 61, avenue de l'Observatoire 75014 Paris France Internet: iers@obspm.fr Terrestrial Frame Section Institut Geographique National B.P. 68 94160 St Mande France Internet: boucher@ign.fr Earth Orientation Section Observatoire de Paris 61, avenue de l'Observatoire F-75014 Paris France Internet: gambis@obspm.fr Celestial Frame Section Observatoire de Paris 61, avenue de l'Observatoire F-75014 Paris France Internet: felicitas@fcaglp.edu.ar SUB-BUREAU FOR RAPID SERVICE AND PREDICTIONS National Earth Orientation Service U.S. Naval Observatory 3450 Massachusetts Avenue, N.W. Washington DC 20392-5420 U S A Internet: dmc@maia.usno.navy.mil SUB-BUREAU FOR ATMOSPHERIC ANGULAR MOMENTUM Climate Analysis Center NOAA/National Weather Service 5200 Auth Road-Room 805 Washington, DC 20233 U S A Internet: salstein@aer.com The Directing Board exercises general control over the activities of the service, including modifications to the organisation and participation that would be appropriate to maintain efficiency and reliability, while taking full advantage of the advances in technology and in theory. It is advised by a group of Corresponding Members, who are kept informed of the activity of the Directing Board and are encouraged to submit comments and suggestions. The secretary of the Board is provided by the Central Bureau. The Members of the Board are, in 1996: C. Reigber International Union of Geodesy and Geophysics B. Kolaczek International Astronomical Union O.B. Andersen Federation of Astronomical and Geophysical Data Analysis Services W.E. Carter VLBI Coordinating Centre C. Veillet LLR Coordinating Centre W.G. Melbourne GPS Coordinating Centre B.E. Schutz SLR Coordinating Centre P. Willis DORIS Coordinating Centre M. Feissel Central Bureau with the permanent participation of D.D. McCarthy Sub-bureau for Rapid Service and Predictions C. Boucher Terrestrial Reference Frame Section of the Central Bureau F. Arias Celestial Reference Frame Section of the Central Bureau D. Gambis Earth orientation Section of the Central Bureau D. Salstein Sub-bureau for Atmospheric Momentum III- Publications . Weekly Bulletin A Earth orientation parameters (x,y,UT1,dy,de): Rapid Service, prediction. First issue covering observation dates in the last week in 1987. . Monthly Bulletin B Earth orientation parameters (x,y,UT1,dy,de) combined solution and individual series. Information on UTC time scale. First issue covering observation dates in January 1988. . Annual Report Earth-orientation parameters, terrestrial and celestial frames of the IERS Reference System: combined solutions and analysis of individual results. First issue, Report for 1988, published in July 1989. . Special Bulletin C Announcement of the leap seconds in UTC. . Special Bulletin D Announcement of the value of DUT1 to be transmitted with time signals. . Technical Notes Reports and complementary information of relevance to the work of IERS on Earth orientation and the reference systems. The IERS Conventions (called earlier IERS Standards are published every three years in this series). The precision of the published results depends on the delay of their availability. For the operational solutions of earth rotation (weekly and monthly bulletins) it is of the order of one millisecond of arc. The prediction accuracy is in the range of 0.005-0.020" for x,y, 0.002-0.015s for UT and 0.002" for dy, de (prediction lags of 10 and 90 days). For the scientific solution of reference frames and Earth orientation, the inaccuracy is lower than 0.0003" (1 cm). The IERS publications are airmailed. Bulletin A is prepared and distributed by the sub-bureau for Rapid Service and Predictions; the other publications are prepared and distributed by the Central Bureau. Bulletins A and Bulletin B are also distributed by e-mail and available on anonymous FTP (File Transfert Protocol). The sub-bureau for Rapid Service and Predictions makes available various results on a Bulletin Board.