Activity Report for 1999-2000 of the International Earth Rotation Service (IERS)

During past years the International Earth Rotation Service (IERS) has undergone a fundamental re-organization that was led by its Directing Board under the efficient chairmanship of Chris Reigber (1995-2000).

The re-organization of the IERS was initiated at the IERS Workshop, Paris 1996, that endorsed corresponding recommendations, and the discussions that followed at the next IERS Workshop at Potsdam, 1998, namely during the 'IERS Retreat'. Shortly afterwards, the new IERS Terms of Reference were formulated and endorsed in March 1999 by the IERS Directing Board; the document is available on the IERS web site (www.iers.org). The main 'driving force' of the proposed changes was the ever increasing complexity of the service since its establishment in 1988, and the efforts to make it less centralized and even more international, with tasks and responsibilities clearly defined and distributed amongst many institutions all over the world. According to the new Terms of Reference, primary objectives of the IERS are to serve astronomical, geodetic and geophysical communities by providing:

  • International Celestial Reference System and Frame (ICRS, ICRF);
  •  International Terrestrial Reference System and Frame (ITRS, ITRF);
  •  Earth Orientation Parameters (EOP) that define the transformation between the ICRS and ITRS;
  •  Relevant geophysical data (i.e., information on the distribution and motion of the atmosphere, terrestrial and oceanic water, mantle, core...);
  • Conventions (i.e., standards, constants, models, algorithms, software...)

The re-organization practically began in November 1999, when the Call for Participation was issued, with deadlines December 10, 1999 (for non-binding Letter of Intent) and February 28, 2000 (for the Proposal). The Letters of Intent that arrived before December 10, 1999 were then reviewed by the IERS Directing Board at its meeting in December 1999 (held in conjuction with the AGU Fall Meeting in San Francisco). It was decided to set up the Proposal Review Committee (PRC) with the task to evaluate all proposals and prepare the corresponding recommendations for the next IERS DB meetings. The list of candidates of PRC was composed, consisting of about 15 knowledgeable scientists, mostly independent both of the IERS DB and proposing organizations. The PRC was then established, under the chair of I. Mueller, at the beginning of 2000. Its first recommendations were delivered and taken into consideration at the IERS DB meeting in Washington (June 2000), and some of them accepted. Nevertheless, there were still several multiple proposals for the same components whose primary scientists were further contacted by the PRC and, in some cases, asked for new joint proposals. These cases were considered and accepted later, so that the IERS DB at its meeting at Frankfurt a.M. (September 2000) was able to take final decisions. Several minor changes of the Terms of Reference were adopted by the 'old' Directing Board at its last meeting in San Francisco (December 2000), mainly reflecting a slightly changed structure of the ITRS PC (see below).

IERS Terms of Reference define the following components of the new IERS:

Technique Centers (TC) that are generally autonomous independent services, cooperating with the IERS. There is typically only one TC per technique, and it provides its operational products to the IERS. At the moment, these are the following:

  • International VLBI Service (IVS);
  • International GPS Service (IGS);
  • International Laser Ranging Service (ILRS);
  • International DORIS Service (IDS) that has not yet been formed, and the technique serves as a Pilot Experiment of the CSTG.

  Product Centers (PC) that are responsible for the products of the IERS. They are as follows:

  •  Earth Orientation PC, responsible for monitoring long-term orientation parameters, publications for time dissemination and announcements of leap seconds. It is placed at Observatoire de Paris, under the leadership of Daniel Gambis.

  • Rapid Service/Prediction PC, responsible for providing Earth orientation parameters on a rapid basis, primarily for real-time users. It is placed at U.S. Naval Observatory, Washington D.C., and is headed by Jim Ray.

  • Conventions PC is responsible for the maintenance of the IERS conventional models, constants and standards. Joint proposal of U.S. Naval Observatory (Washington D.C.) and Bureau International des Poids et Mesures (Sevres) was accepted, under the guidance of Dennis McCarthy and Gerard Petit, respectively

  •  International Celestial Reference System PC, responsible for the maintenance of ICRS and its realization, ICRF. Joint proposal of Observatoire de Paris and U.S. Naval Observatory was accepted, both groups being represented by Jean Souchay and Ralph Gaume, respectively.

  •  International Terrestrial Reference System PC, responsible for the maintenance of ITRS and its realization, ITRF. This was probably the most difficult IERS component to assign. Two different proposals were received, from Institut Geographique National (Marne-la-Vallee) and from Deutsches Geodaetisches ForschungInstitut (Munich). Because the two institutions were not able to submit a joint proposal (as requested by PRC) by the deadline of July 15, 2000, the PRC recommended to adopt a slightly different structure than originally anticipated by the IERS Terms of Reference

  • one ITRS Product Center and multiple Combination/Analysis Centers, with an option of rotating the PC responsibilities between the C/AC's every four years. New Call for Participation for these components was proposed to be issued. The IERS Directing Board at its meeting in Frankfurt (September 2000) decided to modify slightly this scheme; it assigned IGN to become the ITRS Product Center, with Claude Boucher as its representative, and both IGN and DGFI as ITRF Combination Centers. The IERS is open for additional ITRF Combination Centers. In the discussion, a possibility of rotating the PC responsibility among C/AC's was also mentioned, but no specific time schedule for the rotation was decided.

  • Global Geophysical Fluids PC, responsible for providing relevant geophysical data sets and related results. This center, having seven sub-centers, was established only in 1998, and consequently no new Call for Participation was issued. It is headed by Ben Chao of GSFC.

Combination Research Centers that are responsible for the development of combinations from data (or products) coming from different techniques. They are expected to provide their solutions to Analysis Coordinator. There are ten of them (the names of leading scientists are given in brackets):

  • AICAS & CTU, Prague (J. Vondrak);
  • FGS & DGFI, Munich (D. Angermann);
  • FGS & FESG, Munich (M. Rothacher);
  • FGS & GIUB, Bonn (A. Nothnagel);
  • GFZ, Potsdam (S.Y. Zhu);
  • FFI, Kjeller (P.H. Andersen);
  • GRGS, Toulouse (R. Biancale);
  • IGN, Marne-la-Vallee (P. Sillard);
  • JPL, Pasadena (R. Gross);
  • IAA, St. Petersburg (Z. Malkin)

  • Analysis Coordinator that is responsible for long-term and internal consistency of the IERS reference frames and other products, for ensuring the appropriate combination of the TC products into a single set of official IERS products and for archiving them. The designated Analysis Coordinator is Markus Rothacher but, because of his new position and teaching responsibilities at the Technical University Munich, he will be able to take over his new IERS office only in summer 2001. Therefore Tom Herring (MIT) was appointed as the interim Analysis Coordinator.

  • Central Bureau that is the administrative center of the IERS; it is responsible for the general management (according to the directives given by the Directing Board), for coordinating the activities, IERS publications, archiving the products and it also serves as its communication center with the users. It is placed at Bundesamt fuer Kartographie und Geodaesie in Frankfurt a.M., under the direction of Bernd Richter.
  •  Directing Board that exercises general control over the activities of the IERS; its chairperson (elected by the Board from its members) is the official representative of the IERS to external organizations. It consists of two representatives of each of the Technique Centers, one for each of the Product Centers, one for all Combination Research Centers together, a representative of the Central Bureau, Analysis Coordinator, and representatives of the IAU, IAG/IUGG and FAGS. The composition of the new DB is as follows:

TC:

  • IVS: Chopo Ma (NASA/GSFC), Axel Nothnagel (University Bonn);
  • IGS: Carine Bruyninx (Royal Observatory Brussels), Robert Weber (TU Vienna);
  • ILRS: Ron Noomen (Delft University), Peter Shelus (University of Texas);
  • IDS: Pascal Willis (IGN), with the status of non-voting observer;

PC:

  • Earth Orientation: Daniel Gambis (OP);
  •  Rapid Service: Jim Ray (USNO);
  •  Conventions: Dennis McCarthy (USNO)/Gerard Petit (BIPM);
  • ICRS: Jean Souchay (OP)/R. Gaume (USNO);
  •  ITRS: Claude Boucher (IGN);
  • GGFC: Ben Chao (NASA/GSFC);
  • Combinations: Sheng Yuan Zhu (GFZ Potsdam);
  • Central Bureau: Bernd Richter (BKG Frankfurt);
  • Analysis Coordinator: Tom Herring (MIT Cambridge)/Markus Rothacher (TU Munich);
  • IAU: Jan Vondrak (Astron. Inst. Prague);
  • IAG/IUGG: Clark Wilson (University of Texas);
  • FAGS: David Pugh (Inst. of the Oceanographic Science, Wormley).

The candidates for the election of the new IERS DB chairperson were selected by the Nominating Committee (I. Mueller, B. Schutz, F. Arias) assigned by the DB, and Jan Vondrak was elected the new chairman in December 2000. The new IERS Directing Board met for the first time in Nice (March 2000), in conjuction with the General Assembly of the European Geophysical Society.

The necessity of creating one or more data centers with mirror sites appeared during the discussions on the new structure of IERS. Therefore a meeting of IERS specialists devoted to this specific problem was organized in Paris (October 2000). Following the recommendations made there, the DB decided that the IERS Central Bureau should operate a data center to store and archive all products which are necessary for the IERS products and also those which are necessary to re-compute the products. For safety and practical reasons the data center should be mirrored at the Observatoire Paris, CDDIS NASA and at a server in Asia. Parallel to this, the observation data will be archived by the Technique Centers, and the products done by Product Centers will be presented also on their Web/ftp servers.

Most of the new IERS components were operational by the end of 2000, and the new IERS as a whole will be fully operational in summer 2001.