Subject: [IGSMAIL-0842] Dec 94 Workshop and GB Meeting
From: G. Beutler
Date: Tue, 17 Jan 1995 14:43:10 PST

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IGS Electronic Mail      Tue Jan 17 14:43:10 PST 1995      Message Number 0842
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Author: G. Beutler
Subject: Dec 94 Workshop and GB Meeting

Re : December 1994 IGS Workshop
     December 1994 Governing Board Meeting

to : IGS Community

Dear colleagues,

As you all know two important IGS events took place in December 1994 in
California, namely the workshop "Densification of the ITRF through
Regional GPS Networks" at the JPL in California and the third Governing
Board Meeting of the IGS on December 6, 1994 in San Francisco (during
the 1994 AGU Fall Meeting). Let me briefly summarize these events:

Summary of the IGS Workshop
Densification of the ITRF through Regional GPS Networks
-------------------------------------------------------
Four position papers were prepared for the workshop:

Position Paper 1) "Densification of the IGS Global Network"
                   J.F. Zumberge, R.E. Neilan, I.I. Mueller

Position Paper 2) "Constructing the IGS Polyhedron by Distributed
                   Processing"
                   G. Blewitt, Y. Bock, J. Kouba

Position Paper 3) "Network Operations, Standards and Data Flow Issues"
                   W. Gurtner and R.E. Neilan

Position Paper 4) "Densification of the ITRF through Regional GPS
                   Networks: Organizational Aspects"
                   G. Beutler, J. Kouba, R.E. Neilan

These papers are now being finalized to take into account the results of
the workshop. They will soon be available in the proceedings of the
December workshop. It is therefore not necessary to summarize these
papers here. We will instead present the conclusions taken at the
workshop and the action items emerging from these conclusions:

Two years of IGS operations show that frequent and regular comparisons
of the results produced by the IGS Analysis Centers were and are the key
to accurate and reliable products. Furthermore the official IGS orbits
prove that combined products are beneficial to the user community. From
such experiences one has to recommend that the coordinates produced by
different IGS Analysis Centers should be checked in the same way as the
orbits and the erps. The following conclusion was drawn:

     Conclusion No 1:
     ---------------
     One, ideally two Associate Analysis Centers shall perform weekly
     comparisons and combinations of the coordinate solutions of all IGS
     Analysis Centers and of future Associate Analysis Centers analysing
     parts of the densified IGS network.

An agency performing coordinate comparisons and combinations in the way
described in position paper 2 will be called an Associate Analysis
Center of type-2 (AAC type-2), an agency analysing parts of the
(densified) IGS network is called an Associate Analysis Center of
type-1 (AAC type-1).

In view of the fact that seven IGS AC's are in principle ready to
produce weekly so-called free coordinate solutions, and considering that
the Department of Surveying of the University of Newcastle, represented
at the workshop by G. Blewitt, and the Institute of Geophysics and
Planetary Physics of Scripps Institution of Oceanography, represented at
the workshop by Y. Bock expressed their interest to act as AAC's type-2
during such a pilot phase, it was decided to ESTABLISH A PILOT PHASE FOR
AAC'S TYPE-2 AS EARLY AS POSSIBLE IN 1995. The ITRF section of the
IERS, represented by Claude Boucher, Pascal Willis and Zuheir Altamimi
at the workshop promised to accompany this pilot phase by regularly
analysing the products of the AAC's type-2.

In order to launch the pilot phase as soon as possible, G. Blewitt was
asked to come up with a time-table for a one-year pilot phase in January
1995.

The permanent IGS tracking network has grown considerably since 1992.
Although the NUMBER of permanent sites (about 60 today) is impressive,
the actual distribution of IGS sites over the globe is still far from an
ideal distribution in the sense of a regular polyhedron.

The problem of obtaining the desired coverage for the IGS network was
addressed in detail in position paper No 1 (Zumberge et al, 1995).
Concerning the instrumentation of future IGS sites the following conclusion
was drawn:

     Conclusion No. 2:
     ----------------
     IGS stations should be permanent stations wherever possible.
     Although near real-time data transmission is desirable, permanent
     receivers with less-than real-time data communications would be
     acceptable, too.

In order to actually obtain the necessary coverage it was recommended at
the workshop to proceed in the following way:

The CB was asked to write a CALL FOR PARTICIPATION (CFP) identifying
regions for the IGS network densification. This CFP shall be sent out
in March 1995.

The densification of the IGS network leads to a considerable growth of
the daily processing workload.  It must be the primary goal of the IGS
TO AVOID THE SITUATION THAT DATA ARE COLLECTED BUT NOT ANALYSED.  This
is why we ask that each site with an IGS label has to be included in the
solution series of at least one (A)AC.  Additional analyses will have to
be taken over by new or existing IGS Associate Analysis Centers of
type-1 (using the terminology of position paper 2).  It was recommended
at the workshop that a Call for Participation should be issued for AAC's
of type 1.  On the other hand it seemed premature to send out such a
call BEFORE having clearly defined the duties of such AAC's of type-1
and before having a clear picture of the densified network.  Based on
these considerations it was recommended to proceed as follows:

     - A format working group consisting of G. Blewitt, Y. Bock, C.
       Boucher, W. Gurtner, and J. Kouba will come up with a
       Software INdependent coordinate solution EXchange format,
       tentatively called SINEX (!).

     - The expectations to be met by an IGS AAC of type-1 are given in
       position paper No 2.  An extract will be included in the CFP for
       AAC's of type-1.

     - The expectations to be met by an IGS site are given in position
       paper No 3 (Gurtner and Neilan, 1995).

     - A Call For Participation for AAC's type-1 will be delayed until
       the pilot program for AAC's of type-2 has had a few months of
       operation.

Not ALL the problems concerning the densification of the IGS network
could be addressed at the 1994 IGS workshop "Densification of the ITRF
through Regional GPS Networks". But the workshop will be remembered as
the principal milestone of this ambitious project -- provided the
actions outlined above are executed in a timely fashion. The workshop
clearly documented that the innovative spirit within the IGS and the
firm wish to work together in an International, truly Global Frame are
still as strong as in the early days of the IGS.

At the end of the workshop the participants thanked the Jet Propulsion
Laboratory and -- of course -- the Central Bureau of the IGS in
particular, for hosting the 1994 IGS workshop.

Summary of the third IGS Governing Board Meeting
of 6 December 1994 in San Francisco
------------------------------------------------

The following report is based on the minutes taken by J.F. Zumberge.

The third official meeting of the IGS Governing Board took place in the
Civic room of the ANA Hotel in San Francisco on December 6, 1994. It
was started at 4:00 p.m. and it ended around 7:30 p.m.

11 of the 15 Governing Board Members attended the meeting. The meeting
started by the formal approval of the minutes of the second GB meeting.
The next topic was the Densification of the ITRF. In essence, the
recommendations of the workshop as outlined above were accepted and the
corresponding action items approved.

The chairman proposed that an IGS workshop should be organized in 1995
with the principal goals (a) to give an overview over the state of the
IGS and (b) to discuss urgent global analysis issues. It seemed clear
that such a workshop should be attached to one of the meetings in the
field taking place in 1995. Finally the invitation of the
GeoForschungsZentrum (GFZ) in Potsdam to host a three-day workshop from
May 15-17 (immediately following the IERS workshop in Paris) was
gratefully accepted. The invitations will be sent out soon by the GFZ.

The Analysis Center Coordinator gave an overview of his activities. He
pointed out in particular that, beginning with January 1, 1995, the
Analysis Centers will start using the ITRF93 (which actually was done).
For future he recommended to consider atmospheric loading and he pointed
out that one may want to start using site-specific atmospheric
measurements. (This undoubtedly will be an important issue for the 1995
workshop). It implicitly became clear that the orbit combination
performed by the coordinator was extremely successful in 1994, and that
the combined orbits are of greatest use to the IGS community.

The IGS will produce an Annual Report for the first time covering the year
1994. The CB will issue guidelines by the end of January, the final version
of the report will be available by the end of June (in time for the XXI-th
General Meeting of the IUGG in Boulder).

In view of the close technical relationship between the GPS and the
Russian GLONASS the question of what role the IGS should play in this
context was addressed. Everybody agreed that, in principle, the IGS
network or a subnet of it would be ideal for GLONASS, too (communication
problem solved, reference frame defined). No immediate action was
recommended. It was assumed that the IUGG meeting in Boulder may serve
as the platform for first contacts between the GPS and GLONASS
communities.

After a few administrative issues it was finally recommended, that the
IGS should apply to become a FAGS (Federation of Astronomical and
Geophysical Data Analysis Services). The necessary steps are being
taken.

In Summary, the two IGS December events, the IGS workshop and the
Governing Board Meeting were extremely fruitful. If we look back for a
few years at the development of our service - first steps were taken in
1989 in Edinburgh, the IGS Oversight Committee was established in 1991
with the goal to organize one or more test campaigns between 1991 and
1995 (recommendation no 5 at the XX-th IUGG meeting in Vienna), the
official service started on 1 January 1994 - we may indeed speak of a
very efficient and very successful implementation of the IGS.

We should never forget that this development was only made possible
thanks to all the institutions and the individuals devoting considerable
parts of their funding and of their working power to the IGS. Let me
thank you all in the name of the IGS Governing Board for your
contributions to the IGS in the past. Let me express the hope that you
will continue to contribute to the IGS in the same sense and spirit.

Wishing you a Happy New Year I remain with kind regards

                                                    Yours sincerely

                                                    Gerhard Beutler

                                                    Chair,
                                                    IGS Governing Board

[Mailed From: James F Zumberge <[email-masked]>]