Subject: [IGSMAIL-74] IERS Call for GPS Proposals
From: M. Feissel
Date: 19 AUG 1992 10:38:35

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IGS Electronic Mail       19-AUG-1992 10:38:35       Message Number 74
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From:     M. Feissel
Subject:  IERS Call for GPS Proposals
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                INTERNATIONAL   EARTH   ROTATION   SERVICE   (IERS)
             SERVICE   INTERNATIONAL   DE   LA   ROTATION   TERRESTRE

                             CALL FOR PROPOSALS

            +--------------------------------------------------------------+
            !  G P S   P A R T I C I P A T I O N S   I N   T H E  I E R S  !
            +--------------------------------------------------------------+

                                                                       JULY 1992

        In 1989 the IERS Directing Board issued a Call for Proposals for a GPS
Coordinating Centre.  As noted in the Call for Proposals, a GPS Coordinating
Centre was sought to promote GPS experiments and analysis for providing an
improved basis for evaluating potential GPS contributions to the IERS.
Furthermore, the Call stated that the selected Coordinating Centre and
Coordinator would serve in a nonvoting capacity, at least until the end of 1992.

        With the success of various experiments and campaigns, on 1992 May 1,
the Directing Board adopted unanimously the following resolution.

Recognizing the contribution that GPS is already making to the determination
and densification of the Terrestrial Reference Frame, and recognizing the
capability of GPS to determine high frequency (daily and sub-daily) Earth
Orientation Parameters, as demonstrated by the excellent results obtained
during the GIG'91 Campaign, the IERS Directing Board :

1) Adopts GPS as an official technique, co-equal with VLBI, SLR, and LLR,
in the operation of the IERS.

2) Welcomes Dr. William Melbourne as the Principal Coordinator for GPS,
representing the present Coordinating Centre at JPL, as a voting member on
the Directing Board.

3) Calls for proposals from organizations to participate as the IERS
Coordinating Centre, Analysis Centres and other functions as needed for
forthcoming IERS GPS activities. These proposals will be reviewed and acted
upon by the IERS Directing Board in consultation with the Oversight Committee
of the International Geodynamics GPS Service (IGS).

The last item is required to establish now a permanent Coordinating Centre and
Analysis Centres. The GPS Coordinator will be a member of the permanent
Coordinating Centre.

GPS PROPOSALS EXPECTED

Prospective host organizations are invited to submit proposals for
participation in one or more of the following activities:

        o as a coordinating centre, including a Technique Coordinator;

        o as an observing station or a network of stations;

        o as a data collection (and distribution) centre for quick-look and/or
full-rate observational data; such a centre could, if appropriate, also
process the data to form normal-point data for use in analyses, or the task
could be carried out by separate centres;

        o as a quick-look operational centre that would provide rapid-service
results;

        o as a full-rate analysis centre that would determine EOPs, station
coordinates and other parameters to a regular schedule.

        Several of these activities might be carried out by one centre, and
the actual organization would differ according to the number of observing
stations and networks and to the nature of the processing required. There
will be no need for associated analysis centres in the formal structure,
although it is expected that many groups will wish to analyse data provided
by the service. Offers of the deployment of mobile systems for use in improving
the terrestrial reference system would be welcomed. The Board hopes to receive
at least two proposals for each activity, even where only one
centre would be required.

        It is recognized that the determination of the Earth Orientation
Parameters is closely related to the determination of GPS orbits and other
paramaters. As such, it is expected that most GPS participants in the IERS
will also participate in the future International Geodynamics GPS Service
(IGS), which has determination of GPS orbits as a primary activity.
Consequently, responses to this Call for Participation in the IERS should
describe the link of the proposed activities with those in the future IGS.

TERMS OF REFERENCE OF THE IERS

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).

        IERS should provide the information necessary to define a Conventional
Terrestrial Reference System and a Conventional Celestial Reference System and
relate them as well as their frames to each other and to other reference systems
used in the determination of the earth orientation parameters.

IERS is responsible for :

- defining and maintaining a conventional terrestrial reference system based
on observing stations that use the high-precision techniques in space geodesy;

- defining and maintaining a conventional celestial reference system 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.

        IERS consists of a Central Bureau and Coordinating Centres for each of
the principal observing techniques, and is supported by many other organisations
that contribute to the tasks of observation and data processing.

        The Coordinating Centres are responsible for developing and organising
the activities in each technique to meet the objectives of the service. The
Central Bureau combines the various types of data collected by the service,
and disseminates to the user community the appropriate information on earth-
orientation and the terrestrial and celestial reference systems. It can include
sub-bureaux for the accomplishment of specific tasks. The Central Bureau
decides and disseminates the announcements of leap seconds in UTC and values
of DUT1 to be transmitted with time signals.

        The Directing Board is composed of representatives of

- the International Astronomical Union,
- the International Association of Geodesy/International Union of Geodesy
      and Geophysics,
- the Federation of Astronomical and Geophysical Data Analysis Services,
- the Central Bureau,
- each of the Coordinating Centres.

        The chairperson is a member of the Directing Board, elected by the
Board for a term of four years, with the possibility of reelection for one
additional term. He/she coordinates the activity of the Directing Board.
He/she is the official representative of the Service at the meetings of IAU,
IAG/IUGG, FAGS, and other outside organisations.

        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. Most
decisions are expected to be made by consensus or by a simple majority vote.
Changes in the structure, membership and chairmanship of the Directing Board
can be made at any time by a two third majority.

        The secretariat of the Board is provided by the Central Bureau. The
function includes the distribution of papers and the compilation of the annual
administrative and financial reports.

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

THE DIRECTING BOARD OF THE IERS

As of 1992 May 1, the Directing Board of IERS is composed of

        IAU representative  :                   Ya. Yatskiv, Ukraine, Chairman.
        IUGG representative :                   K. Yokoyama, Japan.
        FAGS representative :                   O.B. Andersen, Denmark.
        Central Bureau representative :                 M. Feissel, France.
        VLBI Coordinating Centre representative :       W.E. Carter, USA.
        LLR  Coordinating Centre representative :       C. Veillet, France.
        GPS Coordinating Centre representative  :       W.G. Melbourne, USA.
        SLR  Coordinating Centre representative :       B.E. Schutz, USA.

THE  ORGANIZATION OF THE SERVICE: OBSERVATIONS AND ANALYSES

        The data analysis which yields the values of the Earth Orientation
Parameters (EOP) published by IERS includes several steps, which are summarized
below.

        1- Observations by the VLBI, LLR, and SLR networks.

        2- Analyses (quick-look and refined) by the IERS Analysis Centres. The
quick-look results include only the Earth orientation information. They are
transmitted weekly in parallel to the Rapid Service sub-Bureau and to the
Central Bureau. The refined results include, in addition, information
on the reference frames. They are transmitted yearly to the Central Bureau,
and published in issues of the IERS Technical Notes.

        3- General adjustment of IERS Celestial Reference Frame (ICRF), IERS
Terrestrial Reference Frame (ITRF) and EOP by the Central Bureau, based on the
refi-ned results. This adjustment,
performed yearly, provides the basis for determining the systematic corrections
to be added to the individual series for the following year in or-der to bring
them into the IERS Reference System; these corrections are used in step 4. The
general results are described and published in the IERS Annual Report, Part II.

        4- Determination of EOP by the Central Bureau in the form of normal and
smoothed values at five-day and smoothed values one-day intervals. This involves
the application of the systematic corrections determined in step 3 and
statistical weighting. The results are published in the monthly Bulletin B with
a delay of thirty days between the date of publication and the last date of the
standard solution.

        5- Determination of EOP by the Rapid Service sub-Bureau in the form of
smoothed solutions at one-day intervals. This involves the application of
systematic corrections and statistical weighting. The results are published in
Bulletin A with a delay of about two to five days between the date of
publication and the last available date with estimated EOP. The analyses of
the sub-bureau for Rapid Service and Predictions are described in the IERS
Annual Report, part III.

        6- Prediction of EOP. Bulletins A and B provide predictions of the EOP
for up to ninety days. In addition, the Rapid Service sub-bureau issues each
week predictions at monthly intervals for one year in advance. The predictions
use similar algorithms, based on seasonal filtering and auto-regressive
processing for x, y, UT1 and on an approximate, modelled correction for the
celestial pole offsets.

FORM OF THE PROPOSALS

        Each proposal for participation should be accompanied by appropriate
information that would cover the following matters:

        o the names and locations of the observing stations and/or centres;

        o the extent of long-term commitment to participation;

        o the history of involvement in such activities;

        o the resources (equipment, personnel, communications, etc) that will
          be available for direct use or back-up; and

        o the names and records of the persons who would be responsible for the
          activities; and the name, address and telephone number of a person
          who would be able to provide any further information that might be
          required.

        The Board recognizes that no organization can give a binding commitment
to participate for a decade or more, especially as the Board will not be able
to provide funds for the operation of the Service; moreover, it recognizes that
there might be some advantages in rotating the responsibilities for some of
the tasks between different centres.

Proposals should be sent by 1993 February 1st to

        BUREAU CENTRAL DE L'IERS
        OBSERVATOIRE DE PARIS
        61, Av. de l'Observatoire 75014 PARIS (France)
        Tel. (33) 1 40 51 22 26      Telex : 270776 OBS
                Earn/Bitnet     : IERS@FRIAP51
                        Span    : IAPOBS::IERS
                FAX     : (33) 1 40 51 22 32

with a copy to the Chairman of the IERS Directing Board, Prof. Y. Yatskiv,
at the Main Astronomical Observatory, 252127 Kiev-127, Ukraine.