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IERS Terms of Reference

October 6, 2015


[Please note that the new structure of the IERS set by these Terms of Reference is in place since January 1, 2001, with several modifications after that date. The previous Terms of Reference (1988-1999) can be found in the History section. Previous versions of the new Terms of Reference were printed in the IERS Annual Reports.]

The IERS was established as the International Earth Rotation Service in 1987 by the International Astronomical Union (IAU) and the International Union of Geodesy and Geophysics (IUGG) and it began operation on 1 January 1988. In 2003 it was renamed to International Earth Rotation and Reference Systems Service. IERS is a member of the ICSU World Data System (WDS).

The primary objectives of the IERS are to serve the astronomical, geodetic and geophysical communities by providing the following:

  • The International Celestial Reference System (ICRS) and its realization, the International Celestial Reference Frame (ICRF).
  • The International Terrestrial Reference System (ITRS) and its realization, the International Terrestrial Reference Frame (ITRF).
  • Earth orientation parameters required to study earth orientation variations and to transform between the ICRF and the ITRF.
  • Geophysical data to interpret time/space variations in the ICRF, ITRF or earth orientation parameters, and model such variations.
  • Standards, constants and models (i.e., conventions) encouraging international adherence.

IERS is composed of a broad spectrum of activities performed by governmental or selected commercial organizations.

IERS collects, archives and distributes products to satisfy the objectives of a wide range of applications, research and experimentation. These products include the following:

  • International Celestial Reference Frame.
  • International Terrestrial Reference Frame.
  • Monthly earth orientation data.
  • Daily rapid service estimates of near real-time earth orientation data and their predictions.
  • Announcements of the differences between astronomical and civil time for time distribution by radio stations.
  • Leap second announcements.
  • Products related to global geophysical fluids such as mass and angular momentum distribution.
  • Annual report and technical notes on conventions and other topics.
  • Long term earth orientation information.

The accuracies of these products are sufficient to support current scientific and technical objectives including the following:

  • Technique Centers.
  • Product Centers.
  • ITRS Combination Center(s).
  • Research Center(s).
  • Analysis Coordinator.
  • Central Bureau.
  • Directing Board.
  • Working Groups.

Some of these components (e.g., Technique Centers) may be autonomous operations, structurally independent from IERS, but which cooperate with the IERS. A participating organization may also function as one or several of these components (except as a Directing Board).


The TCs generally are autonomous independent services, which cooperate with the IERS.

The TCs are responsible for developing and organizing the activities in each contributing observational technique to meet the objectives of the service. They are committed to produce operational products, without interruption, and at a specified time lag to meet requirements. The products are delivered to IERS using designated standards. The TCs provide, as a minimum, earth orientation parameters and related reference frame information, as well as other products as required.

The TCs exercise overall control of observations from their specific techniques, archiving, quality control and data processing including combination processing of data and/or products received from their participating organizations. TCs are the various international technique specific services: IDS, IGS, ILRS, IVS, and possible future TCs.


PCs are responsible for the products of the IERS.

Such centers are the following:

  • Earth Orientation Center, responsible for monitoring earth orientation parameters including long term consistency, publications for time dissemination and leap second announcements.
  • Rapid Service/Prediction Center, responsible for publication of semiweekly (possibly daily?) bulletins of preliminary and predicted earth orientation parameters.
  • Conventions Center, under the guidance of the IERS Conventions Editorial Board, responsible for the maintenance of the IERS conventional models, constants and standards.
  • ICRS Center, responsible for the maintenance of the ICRS/ICRF.
  • ITRS Center, responsible for the maintenance of the ITRS/ITRF, including network coordination (design collocation, local ties, and site quality). For this purpose the Center is also responsible to provide the ITRS Combination Centers (see below) with specifications, and to evaluate their respective results.
  • Global Geophysical Fluids Center, responsible for providing relevant geophysical data sets and related computational results to the scientific community.


ITRS Combination Center(s) are responsible to provide ITRF products by combining ITRF inputs from the TCs and others. Such products are provided to the ITRS Center.


Research Center(s) are responsible for carrying out research on a specific subject. They are established by the DB and are related to a corresponding Product Center. Research Center(s) are limited to a term of 4-5 years.


The AC is responsible for the long-term and internal consistency of the IERS reference frames and other products. He is responsible for ensuring the appropriate combination of the TC products into the single set of official IERS products and the archiving of the products at the Central Bureau or elsewhere.

The AC is elected by the DB for a term of four years with the possibility of re-election for one additional term. The responsibility of the AC is to monitor the TC and PC activities to ensure that the IERS objectives are carried out. This is accomplished through direct contact with the independent TC Analysis Coordinators and PC chairs or equivalent. Specific expectations include quality control, performance evaluation, and continued development of appropriate analysis methods and standards. The AC interacts fully with the Central Bureau, the Product Centers and the Research Center(s).


The Central Bureau is responsible for the general management of the IERS consistent with the directives and policies set by the Directing Board, i.e., acts as the executive arm of the Directing Board. The CB facilitates communications, coordinates activities, monitors operations, maintains documentation, archives products and relevant information and organizes reports, meetings and workshops.

Although the Chairperson of the Directing Board is the official representative of the IERS at external organizations, the CB is responsible for the day-to-day liaison with such organizations. The CB coordinates and publishes all documents required for the satisfactory planning and operation of the Service, including standards/conventions/specifications regarding the performance, functionality and configuration requirements of all elements of the Service including user interface functions.

The CB operates the communication center for the IERS. It distributes and/or maintains a hierarchy of documents and reports, both hard copy and electronic, including network information, standards, newsletters, electronic bulletin board, directories, summaries of performance and products, and an Annual Report.


The Directing Board consists of the following members:

  • Two representatives from each Technique Center to be selected by the Technique Center's governing board or equivalent. The two representatives will represent that technique regarding
    a. its network and coordination with other techniques,
    b. the details of the technical analyses.

It is desired that, as part of reciprocity agreements, IERS representatives are to become members of the Technique Centers' directing boards.

  • One representative from each Product Center.
  • Representative of the Central Bureau.
  • IERS Analysis Coordinator.
  • Representatives of IAU, IAG/IUGG and GGOS.

The Chairperson is elected by the Board for a term of four years with the possibility of re-election for one additional term. Eligible candidates are members of the DB and IERS Associate Members. The Chairperson does not vote, except in case of a tie. He/she is the official representative of IERS to external organizations.

The DB exercises general control over the activities of the service and modifies the organization as appropriate to maintain efficiency and reliability, while taking full advantage of the advances in technology and theory.

Most DB decisions are to be made by consensus or by a simple majority vote of the members present, provided that there is a quorum consisting of at least one half of the membership. In case of a lack of a quorum, the voting is by correspondence. Changes in the Terms of Reference and Chairperson of the DB can be made by a two third majority of the members of the DB. If a DB member cannot participate in the meeting, he/she can designate a proxy to attend the meeting and vote in the place of the absent DB member. Any appointment of a proxy by a DB member shall be in writing to the CB prior to the meeting, and is valid only for the meeting.

For the DB to effectively assess the value of IERS services to the user communities, and to ensure that the service remains up to date and responsive to changing user needs, the DB will organize reviews of the IERS components at appropriate intervals. The DB will decide, on an annual basis, those components that are to be reviewed and from time to time may select other activities for review, as it deems appropriate. The Central Bureau provides the secretariat of the DB.

The Board shall meet at least annually and at such other times as shall be considered appropriate by the Chairperson or at the request of five members.


Working Groups may be established by the DB to investigate particular topics related to the IERS components. Working groups are limited to a term of two years with a possible one-time re-appointment. The IERS Analysis Coordinator and the Director of the Central Bureau are ex officio members of each working group, and may send official representatives to meetings which they are unable to attend. Working groups may also collaborate with other scientific organizations like, e.g., IAG, CSTG.

The chair of a working group must prepare, at least annually, a report about the activities of the group to be included in the IERS Annual Report. Working group chairs are invited to participate in DB meetings.

Individuals or groups wishing to establish an IERS Working Group must provide the following at least two weeks prior to the IERS Directing Board Meeting where DB approval is requested.

  • Draft charter clearly specifying:

    • Proposed goals (two pages at maximum),
    • Proposed structure of the group or project,
    • Working plan including schedule / deadlines including the anticipated end of work,
  • Candidate for a chairperson to be appointed by the DB (optional),
  • Initial list of members,
  • Proposed plans for an operational phase (if applicable),
  • Draft IERS Message to inform the IERS community.


Persons representing organizations that participate in any of the IERS components, and who are not members of the Directing Board, are considered IERS Associate Members. Ex officio IERS Associate Members are the following persons:
IAG General Secretary
IAU General Secretary
IUGG General Secretary
President of IAG Commission 1
Chair of IAG Subcommission 1.1
Chair of IAG Subcommission 1.2
Chair of IAG Subcommission 1.4
President of IAG Commission 3
Chair of IAG Subcommission 3.1
Chair of IAG Subcommission 3.2
Chair of IAG Subcommission 3.3
President of IAU Division A
President of IAU Commission A1
President of IAU Commission A2
President of IAU Commission A3


IERS Correspondents are persons on a mailing list maintained by the Central Bureau, who do not actively participate in the IERS but express interest in receiving IERS publications, wish to participate in workshops or scientific meetings organized by the IERS, or generally are interested in IERS activities.

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