Subject: [IGSMAIL-1806] 1998 IGS AC Workshop in Darmstadt
From: G. Beutler
Date: Tue, 17 Feb 1998 5:53:35 PST

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IGS Electronic Mail      Tue Feb 17  5:53:35 PST 1998      Message Number 1806
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Author: G. Beutler
Subject: 1998 IGS AC Workshop in Darmstadt

Dear Colleagues

The 1998 IGS Analysis Center Workshop took place 9-11 February 1998
in Darmstadt. In addition, a business meeting of the IGS Governing Board
was scheduled for Sunday, February 8, a wrap-up meeting of the Governing
Board together with the convenors of the AC Workshop and the authors of the
position papers concluded the Darmstadt IGS events. As usual I try to
summarize the essential events of the Board meetings and of the workshop.

Governing Board Meetings (February 8 and 11)
********************************************

IGEX-98
-------
Pascal Willis, chair of the CSTG Subcommission on "Precise Satellite
Microwave Systems", presented the draft call for participation for the
"International GLONASS Experiment (IGEX)" to the IGS Governing Board. In
essence it is proposed to organize a three months GLONASS test campaign by
the end of 1998. The Experiment is organized by CSTG, it is sponsored by
the IGS, the ION, and the IERS. The call for participation was prepared by
the IGEX steering committee consisting of Pascal Willis (IGN, chair),
Gerhard Beutler (AIUB), Werner Gurtner (AIUB), Guenther Hein (UFAF), Ruth
Neilan (JPL), and Jim Slater (NIMA).

The draft call for participation consists of two parts, a description of
the experiment and the actual call for participation. The IGS involvement
is indeed essential:  Major parts of the IGS infrastructure (network, data
links, data centers) will be used. It is furthermore expected that some of
the IGS Analysis Centers will answer the IGS Call for Participation.

The Steering Committee of the IGEX-98 is fostering participation in the
1998 International GLONASS Experiment IGEX-98 in the following areas:

 - IGEX-98 Coordinating Center
 - IGEX-98 Observing Sites
 - IGEX-98 Data Centers
 - IGEX-98 Analysis Centers
 - IGEX-98 Evaluation Center(s)

All GLONASS satellites are equipped with arrays of LASER reflectors
allowing the SLR community to range easily (!) to the GLONASS satellites. It
was thus decided to closely coordinate the IGEX-98 with the SLR
Subcommission of CSTG (Werner Gurtner from the IGEX-98 steering committee
is the "liaison officer" to the SLR Subcommission). The participation of
the SLR community is essential for validating the results and for the
development of radiation pressure models for the GLONASS satellites.

The receiver situation is of concern to the IGS Board members. In
principle one would like to use uniquely geodetic-type dual frequency
combined GPS/GLONASS equipment (similarly as it was done for the 1992 IGS
Test Campaign). In order to have access to a greater number of receivers
the steering committee decided to be more flexible:  In sequence of
preference, the following receiver types may be used in IGEX-98:

 - Combined dual-frequency GPS/GLONASS receivers
 - Dual-frequency GLONASS receivers
 - Combined single-frequency (L1) GPS/GLONASS receivers
 - Single-frequency GLONASS receivers

Receivers must be collocated with or tied to sites that have well-determined
ITRF coordinates. IGS sites are preferable. The ITRF coordinates should
have an accuracy of 1-5 cm.

Not only the receiver situation, but also the satellite situation has to be
considered as a crucial issue. Today, there are only 14 operational
GLONASS satellites available. Launches of GLONASS satellites have been
announced, however. There is not much that the steering committee can do
to improve satellite availability (!). Should the number of operational
GLONASS satellites fall under a critical level, the IGEX-98 would of course
have to be postponed.

The schedule for IGEX-98 is as follows:

 February 1998  Distribution of IGEX-98 Call for Participation
                through mail e-mail services of the sponsoring
                agencies.
 May            Proposals due
 June           Evaluation of proposal by the Steering Committee
                Review/approval of the schedule
                Designation of the Oversight Committee (including Chair)
                Campaign Planning Meeting
 September 20   Campaign begins
 December 20    Campaign ends
 early in 1999  IGEX-98 Evaluation Workshop (possibly combined with the
                1999 IGS Analysis Center Workshop)

The IGS Governing Board discussed the proposal in detail. It was finally
decided that the Call for Participation should be sent out in February 1998
after a few modifications. The modifications underline the experimental
(as opposed to operation oriented) character of IGEX-98. The chairman
thanked Pascal Willis and the IGEX-98 steering committee for their planning
work.

IGS Densification
-----------------
At the eighth IGS Governing Board meeting in San Francisco (December 1998)
it was decided to take the necessary steps to terminate the Pilot Phase of
the Densification Project as soon as possible, but not before all
discrepancies, errors, etc., in the understanding of station coordinates
(and velocities) were removed (IGS Mail Message 1763). This condition
could not yet be met. The IGS Central Bureau, together with the IGS
Infrastructure Committee are still working on that issue. The basis is the
list of discrepancies published regularly by the Analysis Coordinator.

It is the policy of the IGS Governing Board to come up with a unique IGS
product of coordinates and station velocities. As all three GNAACs are
willing to continue with their activities one has the problem that a unique
series of coordinates has to be formed using the resulting SINEX files
of the three SINEX files. Norman Beck, Chief of Active Control System,
Natural Resources Canada (NRCan), kindly offered in a letter dated January
19, 1998 to produce the SINEX GNAAC combination, based on the three GNAAC
solutions by University of Newcastle, JPL and MIT. The IGS Governing Board
unanimously accepted this offer and asked the chairman to thank NRCan for
providing this service to the IGS community. NRCan will start providing
this combination as soon as possible (probably in March 1998).

As a side issue Norman Beck asked the chairman to explore the IGS
Governing Board's views concerning an EUREF-like activity for North
America. The discussion revealed that the Board and the GNAACs represented
at the business meeting would in fact favour such a development. The EUREF
solution, coordinated by Carine Bruyninx, is (amongst other) most useful to
eliminate all station-related problems. Also, it makes sure that the
solution is actually providing the reference frame for the continent, which
is accepted and used by the European topography and geodetic services. The
chairman was asked to write a letter to the existing and potential RNAACs
in North America encouraging this level of cooperation.

"Densification of the ITRF using GPS" will be again on the agenda of the
ninth IGS Governing Board Meeting, to be held end of May 1998 in Boston. I
hope (and assume) that the Board will be in a position to decide about the
operational phase of the densification issue.

1997 IGS Annual Report
----------------------
Ruth Neilan and Jim Zumberge came up with a new format for the 1997 IGS
Annual Report. They propose to produce the report in two parts
(corresponding to 2 volumes). Part 1 would contain, so to speak, the top
level information (CB report, IGS Analysis Center Coordinator report,
report about current projects, etc.), Part 2 would contain the Analysis
Center reports, the station reports, etc. Part 1 would be edited by the
Central Bureau in a similar way as it was done with the 1996 Annual Report.
Part 2 would be published based on "camera ready manuscripts". In order to
reduce the size of the Annual Report, page limits will be given to the
authors. Both reports will be made available also in electronic form.

The proposal aims at reducing the costs of the Annual Reports and at having
the Annual Report available much earlier.

After extensive discussions and after positive feedback from the Analysis
Centers the Board accepted the proposal. The authors of the 1997 Annual
Report will be notified concerning the expected contributions in the near
future. The Annual report -- if possible both parts, but certainly Part 1
-- should be available in July 1998.

GPS Modernization Process and IGS Involvement
--------------------------------------------
Ruth Neilan informed the Board that she was asked to chair a working group
of the "US GPS Interagency Advisory Council (GIAC)" jointly set up by the
U.S. Department of Defence (DoD) and the Department of Transportation
(DoT). Ruth Neilan views this assignment as an important interface between
the international scientific community represented in the IGS and operators
of the GPS.

The IGS Governing Board in turn viewed this as a very positive development
and encouraged the Central Bureau to play a very active role in this
working group. The hope was expressed that views of the IGS community on
issues like the "second civil frequency" or on the attempt to assign the
frequency range 1559-1567 MHz to Mobile Satellite Services (MSS) (latest
attempt made at the the WRC-97 in Geneva) could more easily be made
known. The CB was in particular asked to coordinate efforts in such
matters with other organizations like, e.g., the ION.

IGS Retreat, December 1998
--------------------------
At the seventh IGS Governing Board Meeting in Rio de Janeiro it was decided
to organize an "IGS Retreat" in December 1997 with the IGS Governing Board
Members and a very limited group of IGS Associates with the goal to come up
with a plan for the future development of the IGS which then should be
discussed by the entire IGS community and the Board (IGS Mail Message No
1683).

About half of the time of the Sunday business meeting of the IGS Governing
Board was devoted to the discussion of the "recommendations and action
items" of the IGS Governing Board retreat in Napa Valley, December 12-14,
1997. The report was prepared by Ivan I. Mueller, who was also the program
chair of the retreat. It was clear that the report could only be discussed
at the business meeting; decisions on this matter will be taken at the next
official IGS Governing Board Meeting (28 May 1998 in Boston). The complete
report containing all recommendations and action items may be retrieved by
ftp (see attachment). Let me point out that comments on the action items
and recommendations are welcome!:  no decisions have been taken so far, the
process may still be influenced till the end of May.

The report contains fourteen recommendations and thirteen action
items emerging from them. Let me comment a few of these recommendations and
action items.

Recommendation 1 proposes to change the name "International GPS Service for
Geodynamics" to "International GPS Service". The acronym "IGS" remains the
same. The Board is in favour of this recommendation.

Recommendation 2 asks the "IGS to produce combined, internally consistent,
global products". Product will include in future orbit parameters, station
coordinates and velocities, earth rotation parameters, GPS clock
corrections, IGS time scale, tropospheric zenith delays, and ionosphere
models. Consistency of all products is the central issue, which was also
discussed at the workshop (see below). The IGS/BIPM Project addresses the
time-related issues.

Recommendation 5 asks that "the global IGS Network should be enhanced in
the overall sense". An important (actually THE important) action item
related to this recommendation is to appoint a Network Manager or
Coordinator, within or outside the CB.

Recommendation 7 asks for a review of the definition of the terms "IGS
Analysis Center", "Associate Analysis Center" at the Analysis Center
Workshop in Darmstadt.

Recommendation 8 recommends that Working Groups be appointed for
"troposphere products", "ionosphere products", for "ITRF densification",
and possibly for others. The working groups should have clear charters and
structures.

Recommendations 9 to 12 are related to the IGS Central Bureau. It is in
particular recommended that the tasks of the CB (as described in the Terms
of Reference) are regularly reviewed, that future tasks are clearly
defined. Moreover, requirements concerning the minimum number of persons
working for the CB were stated.

Recommendation 14 asks the Governing Board to consider forming a committee,
with external participation, with the task to prepare the IGS Long Range
and Strategic Plan.

The above selection of recommendations and action items emerging from the
IGS Retreat 1997 is of course a personal one. Everybody is encouraged to
retrieve the complete report.

The Governing Board considers the "recommendations and action items" of
the IGS Governing Board retreat in Napa Valley, December 12-14, 1997 as
prepared by Ivan I. Mueller as an extremely useful document defining the
development of the IGS at least till the end of the millenium (!). The
Board thanked Ivan I. Mueller for his excellent work.

1998 IGS Analysis Center Workshop (9-11 February, 1998)
*******************************************************
4 topics (see below) were dealt with in detail at the 1998 IGS Analysis
Center Workshop. The first presentation within each topic was a position
paper, topic 4 even was dealt with in two position papers. All of the
position papers were available over the internet prior to the workshop
(ftp-address:  see attachment). The final versions of the position papers
will be available no later than March 15, 1998 under the same ftp-address.
These remarks underline how well the workshop was prepared by the programme
committee, consisting of John Dow, Jan Kouba, and Tim Springer.

The workshop was formally opened on Monday, February 9 at 9 a.m. with a
welcome address by Carlo Mazza, Head of Ground Systems Engineering
Department of ESA, with an introduction by John Dow, and an overview of
previous IGS workshops by Gerhard Beutler.

Topic 1: The IGS Analysis Products and Consistency of the Combination
Solutions (Session Chair: Jan Kouba, Markus Rothacher)
--------------------------------------------------------------------
The position paper entitled "the IGS Analysis Products and the Consistency
of the Combined Solutions" written by T.A. Springer, J.F. Zumberge, and J.
Kouba reviewed the quality, consistency, and reliability of current IGS
analysis products (orbits, Earth orientation parameters, station
coordinates, and clocks). The paper focused on current procedures to derive
these products, on reporting and feedback. Seven recommendations were given
at the end of the paper. All of them were accepted, some will ask for
significant work by the IGS Analysis Centers in the near future. As the
proceedings of the workshop (containing all position papers and
resolutions) should be available rather soon, and as people interested in
the resolutions may retrieve preliminary versions of the position papers
under the ftp address mentioned, we may confine ourselves to highlight
only a few of these resolutions.

First of all it is recommended that the IGS ACs include ephemerides for ALL
operational satellites in the daily SP3-files, and that these ephemerides
are characterized by MEANINGFUL accuracy codes. No format changes are
necessary for this step, most of the analysis centers already provide such
accuracy information. It was also discussed, however, that the user
community of IGS products must be made aware of these accuracy codes, and
that this community should be strongly encouraged to make use of these
codes. This aspect might be more important in future, when more orbit
information of "modest quality" will available (due to this resolution).

Precise single point positioning developed by Zumberge et al. is used
extensively today. Consistency of orbit and clock information is crucial
for this technique. The required consistency level (of millimeters) is much
easier to achieve if the same software package is used to produce the
global products (orbits and clocks) AND the coordinates using the single
point positioning technique. It was/is most encouraging to see that
already today, thanks to an essential upgrading of the combination
technique, the consistency level for the combined IGS products is not far
away from the best possible consistency level that may be reached (using
one and the same software). It seems feasible that sub-centimeter
point-positioning using IGS products should be possible in the very near
future.

Other recommendations dealt with the "densification project". It was
recommended that deadlines in compliance with other deadlines in the IGS
are used, that EOP information is included by all analysis centers in the
GNAAC solutions, and that all discrepancies/errors in the RINEX files are
removed.

Also, the minimal requirements (performance-wise) to become an IGS Analysis
Center were reviewed (and probably clearly defined for the first time). As
this recommendation was extensively discussed and modified at the workshop,
it is advisable to wait for the final version of this position paper.

There were other interesting contributions in the first session. Jim
Zumberge presented a technique at JPL to produce in an efficient way
high-rate GPS clocks, Wolfgang Soehne from GFZ presented the GFZ procedures
developed for the same purpose. Jim Ray gave a short status report of the
IGS/BIPM project:  the call for participation was issued in January, the
next phase will consist of evaluating the proposals received in spring
1998.

Topic 2: Orbit Prediction and Rapid Products (Session Chair: Tim Springer,
John Dow)
--------------------------------------------------------------------------
Tomas Martin Mur (ESA), Tim Springer (CODE) and Yoaz Bar Sever (JPL)
reviewed the procedures for "Orbit Prediction and Rapid Products" in
the position paper for topic 2. With the increasing demand for close to
real-time products this issue becomes more and more important. It came out
very clearly that data availability is THE critical issue. Global coverage
is far more important than the number of stations (provided a minimum
number of about 30 stations is available).

The paper also reviewed the prediction techniques used by individual IGS
Analysis Centers and in the combination. Usually, IGS predictions are much
better than broadcast orbits (the former, when compared to the IGS final
orbits are of about 30-50 accuracy (extrapolation over 2 days), the latter
are of 2-3 meter accuracy). There are exceptions, however, which are not
always predictable. Two measures may improve the reliability of IGS
predicted orbits:  (a) reduction of the delay of data availability (see
primary recommendation below), (b) reduction of the number of "unknown"
parameters for prediction process.

New orbit models developed by Yoaz Bar-Sever at JPL and by Tim Springer at
CODE are promising in area (b). Only improved data transmission may help
in area (a):  Therefore, the first and probably the primary recommendation
of the position paper asks the operational and global data centers to give
highest priority to the delivery of stations outside Europe and North
America (!). This does not mean, of course, that data from Europe and North
America are not important; but due to the usually excellent infrastructure
ftp retrieval guarantees quick availability of a sufficiently high
number of stations (data outside these areas often have to be retrieved by
the operational centers by telephone or other links).

All in all seven recommendations were given in the position paper for Topic
2. The first three addressed data availability (including more frequent
than daily data download), the third recommends extensive tests of the two
new radiation pressure models (which are made available by CODE and JPL) by
all IGS ACs. The other three resolutions dealt with EOP series to be used
with the predictions, studies to improve the accuracy codes for prediction,
and the use of the NANU messages to reduce the number of blunders. An
important issue, the change of the deadline for the IGS Analysis Centers
to deliver the rapid orbits/eops to 4 p.m. U.T. by January 1, 1999
(from 9 p.m. U.T.), was extensively discussed at the workshop. A
recommendation related to that topic will be contained in the final version
of position paper 2.

The position paper was followed by technical papers related to topic 2:
Tim Springer presented his "latest and greatest" radiation pressure model
and compared it to the model developed by Bar-Sever. Jim Zumberge
addressed the problem of identifying mismodeled satellites in GPS predicted
orbits. A presentation by M. Romay-Merino dealt with considerations
concerning real-time orbit computation for navigation using orbit
predictions of the GPS, GLONASS, etc., in the context of GNSS. A
contribution by P. Silvestrin described the GRAS (GPS/GLONASS) receiver
being developed by ESA for support of atmospheric sounding and other
applications.

Topic 3: IGS Reference Frame Realization and Contribution to ITRF (Session
Chair: Mike Watkins, Gerhard Beutler)
--------------------------------------------------------------------------
The position paper by J. Kouba, J. Ray and M.M. Watkins addressed "IGS
Reference Frame Realization" within/by the IGS. It was stated in particular
that the current set of 13 ITRF94 stations and the current IGS approach to
realize the ITRF are no longer appropriate. A new set of about fifty
reference frame stations (based essentially on an IGS history of station
coordinates AND the new ITRF96 as made available through the IERS) are
about to replace the "old" set of 13 stations. It is expected that this
measure will "dramatically" improve the IGS rapid EOPs. This in turn will
improve the Bulletin A values of the IERS.

The paper also compares in detail the ITRF96 station positions and
velocities with the purely IGS derived quantities for the selected fifty
stations (and subsets of it). The agreement is excellent, indeed. It is
therefore natural that recommendation 1 demands the IGS to adopt ITRF96
as early as March 1, 1998.

Other recommendations deal with technical aspects of producing the SINEX
solutions, like, e.g., the inclusion of EOPs. Last but not least, it is
recommended that a "super"combination of G-SINEXes for station coordinates,
velocities and EOPs is researched and initiated on behalf of the IGS. The
participants of the workshop were very much pleased to learn that NRCan
would take on this new combination task (compare report about GB Meeting,
topic "densification").

Very interesting and informative presentations concerning the establishment
of ITRF96 followed the position paper. It became quite clear that
the IGS is an important contributor to the ITRF. The histograms dealing
with coordinate accuracies are interesting, as well. It might be
worthwhile to look into the technique specific aspects:  it seems in
particular that the distribution of SLR-derived height errors supports the
conclusion that, due to the unproblematic modeling of the troposphere in
SLR, the SLR determined heights may significantly contribute to the height
datum of the ITRF96.

Markus Rothacher et al. summarized their attempts to extract
short-period nutation terms from CODE/IGS eop series. Apparently, for
periods up to about 20 days, the results obtained by GPS are of equal or
better quality than those obtained by VLBI. The work was motivated by the
simple idea that "there is no reason NOT to solve for nutation drifts, if
one is solving for lod-values"! It is expected that the results can be
significantly improved, if a more appropriate orbit model (radiation
pressure model) is adopted.

Geoff Blewitt et al. proposed to extract "fiducial-free Euler vectors"
from the GNAAC Polyhedron time series. The method presented allows it
very well to separate "normal" plate motion (represented through the Euler
vectors, resp. their first derivatives) from "abnormal" (e.g., subsidence)
or "apparent" (e.g., induced through antenna changes ...) motion. It might
be worthwhile to explore the interest within the IGS and the IERS community
for such vectors as a regular IGS product.

Topic 4: IGS Products for Troposphere and Ionosphere (Session Chair: Gerd
Gendt, Mark Schenewerk)
-------------------------------------------------------------------------

TROPOSPHERE
The position paper "IGS Combination of Tropospheric Estimates - Experiences
from Pilot Project" was presented by Gerd Gendt from the GFZ Analysis
Center. GFZ was gaining experience since more than one year of comparing
and combining troposphere estimates for about 100 sites of the IGS
Global Network stemming from individual IGS Analysis Centers.

Despite the fact that rather different processing options were used
by the Analysis Centers (different levels of differencing, different
binning, different cut-off angles) the consistency level reached is in
general quite good. There was general agreement that the combined series
of total zenith path delays for the entire IGS network are of interest for
climatological studies. Gerd Gendt recommends furthermore that the
troposphere combination product should become an official IGS product, that
the weekly summary reports are made publicly available (in the IGS report
series), and that the product distribution is performed using the ftp
server of GFZ.

The IGS troposphere product would be of much greater value, if a
significant number of permanent, accurate, reliable surface meteorology
measurements series would be available. This is a station specific issue
to be addressed by the Central Bureau, the Infrastructure Committee and the
future Network Coordinator.

Gerd Gendt's recommendations were unanimously accepted. We are thus
looking forward to see the announcement through IGS-mail that official IGS
troposphere products are available.

Matthias Becker and Georg Weber from BKG Frankfurt (former IfAG)
presented a study to use the German permanent GPS network (GREF) to extract
regional troposphere information on a routine basis. The results are
promising and should be seen as an attempt to make optimum use of
a permanent network.

Yoaz Bar-Sever discussed troposphere gradient estimates performed at the
JPL Analysis Center. He concludes that gradient estimates are significant
and tend to improve station coordinate repeatability. The drawback has to
be seen in the considerably increased number of parameters. Comparisons of
monthly mean values for the JPL gradient parameters with those of the CODE
Analysis Center show a good agreement. More work has to be done in this
area.

IONOSPHERE
The position paper "IGS Products for the Ionosphere" was given by Joachim
Feltens (ESA) and Stefan Schaer (CODE). They reviewed the ionosphere
related activities within the IGS in previous years and they came up with
a list of ten potential participating institutions in a future "IGS
ionosphere service". Based on an e-mail inquiry they furthermore gave an
overview of analysis methods and models used by the institutions mentioned.
An important part of the presentation dealt with the definition of a future
IGS ionosphere product. They recommend that all IGS ionosphere products
 - must be based on the IONEX format,
 - should refer to a two-dimensional grid in a (single layer) shell,
 - should refer to the same shell height,
 - should use identical reference epochs for subsequent ionosphere models,
 - that one, maybe two, time resolutions have to be agreed on, and
 - that naming conventions for ionosphere model files have to be
   defined.
The authors and the interested institutions are convinced that the
development of an IGS ionosphere product makes sense and that a continuous
series of IGS products should be produced at least over one full 11 years
cycle of solar activity. It is of particular importance that the IGS
models are covering the next period of maximum of solar activity (years
2001-2003). The key recommendation was to establish a pilot phase for such
an IGS ionosphere service as soon as possible.

It was most encouraging that the experts in the field of ionosphere
physics, in particular Drs. N. Jakowski (DLR Neustrelitz), R. Leitinger
(TU Graz), and R. Warnant (Royal Observatory of Belgium, Brussels), and L.
Wanninger (TU Dresden) were attending the workshop to give their input for
the development of an IGS product. Their presentations showed that many
activities in the ionosphere community are regional in nature -- and that
there are good reasons for this. It became clear that the IGS (at least in
a first phase) should stay out of regional ionosphere modeling, but should
rather focus on global aspects. One had to conclude from the discussions
that there is a great interest of the ionosphere community in a continuous
series of global IGS ionosphere models.

That the modeling capabilities were significantly improved over the
last few years emerged from two technical presentations given by Stefan
Schaer and by Joachim Feltens. The former presentation showed (among
other) that the parameters of the CODE models may be successfully
predicted, the latter presentation was also addressing mathematical aspects
using a so-called "Chapman profile approach".

In the discussion portion of the session and in the wrap-up meeting at the
end of the workshop the following procedure was proposed:

 - Joachim Feltens and Stefan Schaer, in close cooperation with the
   existing "IGS ionosphere club", should come up with
   - a proposal for global IGS ionosphere products (including the
     specification of parameters, formats, etc.)
   - a clear proposal how to proceed (test phase, pilot phase, etc.)
   - a proposal for the structure of the working group (what
     positions have to be created (e.g., IGS (Associate) Ionosphere
     Analysis Centers, Ionosphere Combination Center, Validation Center),
   - a list of members for the future IGS Ionosphere Working Group.

   These specifications should be included in the final version
   of their position paper.

 - John Dow and Gerhard Beutler should
   - draft a general "charter" for setting up Working Groups within the IGS
     and circulate this draft within the Governing Board,
   - develop in close cooperation with the "ionosphere club" the
     charter for the ionosphere working group and circulate this draft
     within the "ionosphere group" (which probably is the nucleus for the
     working group).

 - Assuming that the structure of the ionosphere working group is
   acceptable to all parties interested in IGS ionosphere monitoring, the
   ionosphere working group should be established by the IGS Governing
   Board by the end of May 1998 in Boston.

This procedure was unanimously accepted by the IGS Governing Board and the
session convenors at the wrap-up meeting on Wednesday, February 11. It
should thus be possible to start an IGS pilot ionosphere service in the
near future.

The workshop was concluded with a session addressing topics other than
those treated in the previous four sessions. Let us mention in particular
presentations by T. Martin-Mur and C. Garcia-Martinez (absolute and
relative orbit determination using spaceborne GPS receiver), Y. Bar-Sever
(low elevation tracking of TurboRogue receivers, site specific antenna
phase center calibrations), H. Habrich (processing of GLONASS and combined
GLONASS/GPS observations), and by Ruth Neilan (GPS modernization effort in
the US).

Hospitality experienced in Darmstadt
------------------------------------
As one may conclude from the above report, the Darmstadt IGS event really
was a WORKshop. That the IGS Analysis Centers form a very dynamic group
of enthusiasts became also clear at the reception on Monday evening and at
the dinner at Jagdschloss Kranichstein. Despite its name there was no
hunting before the dinner, one even had the option of a vegetarian menue
(and this in a Jagdschloss -- "o tempora, o mores"!).

The Analysis Centers took the opportunity to thank Jan Kouba for his
personal engagement and his great performance as IGS Analysis Coordinator.
A Swiss railway clock presented to him will undoubtedly help him to
understand the subtleties of the IGS/BIPM project. The clock is also
complicated enough (it has at least two buttons and may be used in at least
two different ways, e.g., as a pocket clock or as a clock on his desk) to
represent a challenge for his technical skills. Jan will continue to serve
as IGS Analysis Center Coordinator till the end of 1998. As the next IGS
AC Workshop will take place only in 1999, the Darmstadt workshop was
presumably the last workshop with Jan Kouba "in command" as AC coordinator.

The chairman also took the opportunity at the dinner to express the
gratitude of all workshop participants to the local organizers from ESA, in
particular John Dow, his wife Roberta, Siegmar Pallaschke, Rolf Muench, and
Hiltrud Grunewald for their perfect organization of the 1998 IGS events in
Darmstadt.

                                                      Gerhard Beutler
                                                      Chair,
                                                      IGS Governing Board

Attachment: How to find position papers and retreat recommendations
----------
            ftp nng.esoc.esa.de
            user: anonymous
            cd pub
            cd gps_data
            cd PosPapersACWS
            dir
            get ...
            bye

[Mailed From: GERHARD BEUTLER <[email-masked]>]