Subject: [IGSMAIL-141] Minutes of Goddard Meeting 1992
From: Gerhard Beutler
Date: 1 DEC 1992 15:35:11

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IGS Electronic Mail        1-DEC-1992 15:35:11       Message Number 141
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From:    Gerhard Beutler 
Subject: Minutes of Goddard Meeting 1992
         -------------------------------

Summary of the Goddard 1992 IGS Oversight Committee Meeting
___________________________________________________________

This report is (a) late, (b) not (yet) complete. I would like to ask
the working group leaders for their help ! Thank you very much in
advance.

The report is based on the notes received from Pat Dewegeli (JPL),
Peter Morgan (U of Canberra) (both covering the entire 2 days), on the
working group reports from Ulf Linquister, Peter Morgan, Ivan Mueller,
and myself.

General Remarks :
_______________

The 1992 Goddard workshop of the IGS Oversight Committee followed the
pattern of the preceeding Goddard workshop (October 1991):  A plenary
session took place on Thursday, October 15 in the afternoon, Friday
morning was reserved for working group meetings, the working group
meetings were presented and the action items set up in the plenary and
closing session Friday, October 16 in the afternoon.

The material of this report together with other information (campaign
summary and announcement/set up of the Berne meeting) should flow into
an IGS Newsletter (to be prepared by Ruth Neilan and her
IGS-collaborators at JPL).  Hopefully such a Newsletter will be
available by the end of January 1993.

Plenary Session, Thursday 15 October 1992
_________________________________________

The session was moderated by Joe Engeln, vice-chairman of the
oversight committee. It was generally agreed that the 1992 IGS
campaign (21 June - 23 September 1992) was a great success: Data
acquisition, data transfer to the network centers, and data management
at the network centers worked surprisingly well : no serious
complaints came from the primary users, the processing centers. The
network centers also made the products of the processing centers
available to all scientific users.  First comparisons showed the
high consistency of the individual) products, but also revealed that a
considerable effort is necessary to get rid of datum problems etc.
But, it should be pointed out again, the level of agreement is
encouraging.

The following working group leaders presented their view of the 1992
IGS events :

 - Werner Gurtner : Standard GPS Data Exchange
 - Peter Morgan   : Communications
 - Claude Boucher : Reference frame issues
 - Ulf Liquister  : Stations/Data Acquisition/AS Data
                    Completion of CORE Network
 - Clyde Goad     : Analysis Center Coordination
 - Bernard Minster: Epoch'92
 - Ivan Mueller   : Management issues

The first five working groups were those set up one year ago at
Goddard, Bernard Minster's working group was formally set up at this
meeting, it proved to be necessary to set up an ad hoc working group
on managenemt issues for this meeting.  Since these working groups
continued their work on Friday it does not make sense to discuss them
here individually (see attached reports plus information in the
summary session).  We try instead to focus on the issues that proved
to be crucial:

Ulf Linquister was replacing Ruth Neilan as working group leader (Ruth
could not attend the workshop this time). Among other agenda items he
had to address the performance of the Rogue receivers under AS :
Starting with August 1, AS was turned on for a varying number of
satellites on most of the weekends. The Rogue switched into a squaring
mode when tracking these satellites, but data was not handled
correctly by the software active in most of the Rogue receivers in the
IGS Core network. Ulf stated that the problem was isolated and that a
new software release (to be sent out in November 1992) would cure this
problem. This issue is of crucial importance since it must be expected
that in future AS will be turned on not only on weekends.

Data collection, data transfer, and data processing continued on a
"best effort basis" after the official end of the 1992 IGS campaign.
Ivan Mueller presented the idea to set up a n IGS Pilot Service,
starting on November 1 1992 to bridge the gap between the end of the
1992 IGS campaign and the start of the official service. He also
discussed the IERS call for participation (of GPS as an official IERS
technique) : In view of the situation created by the success of the
IGS campaign it might make sense to seek a collaboration on a higher
level between IGS and IERS. These issues were discussed at length,
action items were postponed to Friday.

It was generally agreed that the feedback from IERS (Radid Service and
Central Bureaa) to the relevant IGS products was excellent. It was
suggested that similar analyses should be done with the orbits --
after all orbits are the primary interest of the IGS.

Plenary/Closing Session, Friday 15 October 1992
_______________________________________________

Again the session was moderated by Joe Engeln.

Summary of Working Group Reports :

1. Standards for GPS Data Exchange (Werner Gurtner)

The RINEX data exchange worked properly during the campaign. Problems
mainly occured due to the "human factor" (changing site/antenna/...
names in the files). Rinex needs to be modified under AS.

2. Analysis Center Coordination (Clyde Goad)

It was first stated that the processing centers in principle followed
the guidelines distributed in May (IGS=IERS standards). Then an
overview over the orbit comparisons performed so far was given. A
routine comparison of orbits (using Helmert transformations between
the products of all centers) will be set up for the Pilot service.
It was also argued that all processing centers should re-process the
global data from the epoch campaign agian -- provided that new
aspects/data etc showed up since the first processing. These data sets
should then be used to come up with official IGS orbits for Epoch'92.

3. Reference Frame Issues (Claude Boucher)

The work at IGN aims at establishing, maintaining, and distributing
the catalogue of Core (and other) sites together with the relevant
information (coordinates, antenna excentricities, etc.). This
catalogue will be updated with IGS global/regional free network
solutions. These should be made available to IGN before the end of
the year.

4. Stations/Data Acquisition/AS Data, Completion of CORE Network

The Roge/AS problem was discussed in detail (see summary above and
working group reports below).  New Rogues within the USA will become
operational soon.  JPL stations are fully automated, data transfer
will be switched from telephone modem to internet.

5. Epoch'92 (Bernard Minster)

It was not possible at the meeting to give a clear and complete
overview over Epoch'92. More information should be available at the
AGU meeting in San Francisco. One of the main topics of the IGS
oversight committee business meeting

     Room: Twin Peaks       Location: Ramada
     Time: 5:00pm-9:00pm    Date: Thursday, Dec 10, 1992

will be devoted to Epoch'92. It was clear however that the regional
concept worked pretty well in Europe, Japan, Australia/Asia, the major
unresolved problem being the (north and South) American region.

It also was argued that in future Epoch campaigns can be not only
organized but also scheduled regionwise -- making full use of the
climatic peculiarities of a more or less spherical earth.

6. Management Issues (Ivan Mueller)

The IGS PILOT-SERVICE will start on 1 November 1992. This decision
was taken unanimously. In the new undertaking the emphasis is on
the SERVICE (showing up twice in the title), meaning that (a) a better
adherence to standards on all levels has to be reached and that
(b) the core and the fiducial network have to be completed.

In these coordination tasks the Central Bureau and the Analysis Center
Coordinator have to play important roles, the former concentrating on
observational aspects, the latter on processing aspects.  It is clear
that these roles have to be based on the decisions taken in the
working groups.  In particular it is expected that a routine quality
control for the orbits is set up by the analysis center coordinator
for the period of the IGS PILOT SERVICE.

Bernard Minster was officially declared responsible as coordinator for
Epoch'92 and for future similar experiments.

The processing centers should reprocess the core data of Epoch'92 with
the state of knowledge they hav today.  The IGS analysis center
coordinator will come u with a suggestion for the official IGS
orbit(s) for this time period.

The Fiducial Network Plan will be provided by Bernard Minster.  Future
Epoch Campaigns will be organized, but only a regional and not a
global coordination of such events will be required.

IERS call for participation was (due 1 February 1993) :  This issue
should be discussed with the IERS Steering Board in view of the new
situation created by the obvious success of the 1992 IGS Test
Campaign. The chairman was asked to write the draft of a letter to the
IERS Board. Meanwhile this letter was written, circulated among the
Oversight Committee Members, edited and sent out (letter included
below).

Jan Kouba from Energy, Mines, and Resources Canada was formally nominated
as member of the IGS oversight committee.

Action Items (Summary)
____________

1.  Compilation and distribution of a receiver/antenna name list
    (Central Bureau).
2.  Use of the site names and site information given in the IGS site
    catalogue by the operational centers (Central Bureau).
3.  Unification of Rinex files under AS conditions. (ad hoc working
    group).

4.  IGS Pilot Service starts 1 November 1992
5.  The analysis center coordinator will set up a regular (weekly)
    orbit comparison (quality check) for the pilot service.
6.  For the time frame of Epoch'92 the processing centers will compute
    the best possible orbits as soon as possible (but before the end
    of 1992). This material will be analyzed by the analysis center
    coordinator. An attempt will be made to produce an official
    IGS orbit for that time interval.

6.  Letter to IERS Board to discuss coordination between IGS/IERS
    (see Appendix)
7.  B. Minster was nominated as coordinator for epoch related
    activities. He will come up with the fiducial network plan.
8.  There will be a business meeting of the IGS oversight committee
    at the AGU meeting in San Francisco (date/time/location see above)

*******************************************************************************
Appendices
----------

Working Group Reports
_____________________

Completion of CORE Network (Ulf Linquister)
-------------------------------------------

The first item of discussion was: which are the Core sites versus the
fiducial sites for the GPS Global Network (GGN). This question has been
discussed and decided on before by other working groups, however,
what is needed now is a working definition of the Core sites which are
currently operating or will be in the near future (in the next 12 months).
The reason for selecting a smaller number of stations as Core sites, is
that the quantity of data to transfer to all agencies and to process and
store is becoming in many cases prohibitive (P. Morgan among others raised
this point). For most applications a smaller number of Core sites
will yield all the necessary products of interest (global GPS orbits,
Earth Orientation Parameters, etc.).

We decided to distinguish between primary and secondary sites, where
the criteria for a primary Core site were:

1. Sites lives up to the GIG'91 or IGS standard (dual-band P-Code
receiver; remote & electronic access; monumented, etc.).
2. Sites will be continuously operating for the foreseeable future.
3. Sites should be able to deliver data within 48 hrs.
4. Sites are co-located with other space geodetic instruments (VLBI, SLR)
and/or instruments of geophysical interest (seismic, gravity, magneto, etc).
5. Sites are geographically well distributed.
6. Sites will be installed within the next 12 months and fullfill the
above criteria.

and for a secondary site the criteria were:

1. Site lives up to the IGS standard (see 1. above).
2. Sites will be continuously operating for the forseeable future.
3. Sites cannot deliver data within 48 hrs, but satisfies 1 & 2.
4. Site is near a primary site, but otherwise fulfills
the primary site criteria (hence it is a hot backup for a
primary site and/or is used for regional densification).
5. Site will be installed after 12 months, but otherwise fulfills
the primary site criteria.

Most of the above must be familiar for anyone sitting through the
earlier working group selections of Core sites and there is no need
to reinvent the wheel here - most of the sites selected below will
be identical to the original site selection.

The following sites below where selected as primary sites (for
the next 12 months):

Table 1.

Site name       Institution     Receiver Type   Install         Comment
------------------------------------------------------------------------
Algonquin       EMR             Rogue SNR-8     in [ALGO]
Tidbinbilla     DSN/NASA        Rogue SNR-8     in [TIDB]
Fairbanks       NASA            Rogue SNR-8     in [FAIR]
Goldstone       DSN/NASA        Rogue SNR-8     in [GOLD]
Hartebeestoek   CNES                  SNR-8     in [HART]
Kokee           NASA                  SNR-8     in [KOKB]
Kootwijk        Delft                 SNR-8     in [KOSG]
Madrid          DSN/NASA              SNR-8     in [MADR]
Maspalomas      ESA             Rogue SNR-8C    in [MASP]
Matera          CDGS/Italy            SNR-800   in [MATE]
McMurdo         ARL/NASA              SNR-8     in [MCMU]
Ny Alesund      SK                    SNR-8     in (1/93)  replace by TR [NYAL]
Onsala          OSO                   SNR-800   in [ONSA]
Penticton       PGC                   SNR-8     in [DRAO] (formerly [PENT])
Santiago        CEE/NASA              SNR-8     in [SANT]
Pamatai         CNES                  SNR-800   in [PAMA]
Taipei          IES                   SNR-800   in [TAIW]
Tromso          SK                    SNR-8     in (1/93)  replace by TR [TROM]
Usuda           ISAS                  SNR-8     in [USUD]
Wettzell        IfAG                  SNR-800   in [WETT]
Yarragadee      NASA                  SNR-8     in [YAR1]
Yellowknife     EMR                   SNR-8C    in [YELL]

Arequipa        NASA            TR              4/93 [AREQ]
Darwin          Auslig          Ashtech         3/93 [DARW]
Easter Isl.     CEE/NASA        TR              2/93 [EISL]
Fortaleza       NGS/NOAA        TR              1/93 [FORT]
Hobart          NGS/NOAA        TR              1/93 [HOBA]
Hofn            SK              TR              6/93 [HOFN]
Kerguelen       CNES            Rogue SNR-8C    6/93 [KERG]
Kitab           GFZ             Rogue SNR-8     in [KITA] communiq >> 48 hrs
Kourou          ESA             Rogue SNR-8C    in [KOUR] communiq >> 48 hrs
Kwadjalein      NASA            TR              6/93 [KWAD]
Richmond        NGS/NOAA        Rogue SNR-8/TR  in (1/93) replace by TR [RCM2]
Westford        NGS/NOAA        TR              1/93 [WEST]
-------------------------------------------------------------------------

The following sites are secondary Core sites:

Table 2.

Site name       Institution     Receiver Type   Install         Comment
------------------------------------------------------------------------
Albert Head     PGC             Rogue SNR-8C    in [ALBH]
Graz            ISR/IGN         Rogue SNR-8     in [GRAZ]
Herstmonceux    RGO             Rogue SNR-8C    in [HERS]
JPL Mesa        NASA            Rogue SNR-8     in [JPLM]
Metsahovi       FGI             Rogue SNR-8C    in [METS]
Pinyon Flats    SIO             Ashtech P-XII3  in [PINY] (or [PIN1])
St. Johns       EMR             Rogue SNR-8C    in [STJO]
Scripps         SIO             Ashtech P-XII3  in [SCRI] (or [SIO2])
Townsville      NGS/NOAA        TRIMBLE 4000ST  in [TOWN]
Vandenburg      SIO             Ashtech P-XII3  in [VAND] (or [VNDP])
Wellington      NGS/NOAA        TRIMBLE 4000ST  in [WELL]
Zimmerwald      FOT             TRIMBLE 4000ST  in (93/94) repl.by 4000SE [ZIMM]

Africa, North   SK              TR              93/94
Africa, West    SK              TR              93/94
Africa, East    SK              TR              93/94
Antarctica      Auslig          ?               6/93 ? (sites:Davis/Morsen)
Azors           SK              TR              93 ?
Bangalore       GFZ             TR              ?
Churchill       EMR             Rogue SNR-8C    4/93
Jos, Nigeria    NASA ?          TR              ?
Greenbelt       NASA            TR ?            1/93
O'Higgins       IfAG            ?               ?
Riyadh          NASA/SES ?      TR              ?
Russia/CIS      SK              TR              93-95 ?
Tristan de C.   NASA ?          TR ?            ?
Tsukuba         GSI             TR ?            3/93 ?
Wellington      NGS/NOAA        TR ?            ?
-------------------------------------------------------------------------

Hence 34 sites (22 currently operating) constitues the completed Core
Network for the next 12 months. Additional sites and adjustements
will have to be corrected for in the future. The action items for
each agency would be to complete the scheduled installation of
the Core sites from the tables above.

*******************************************************************************

Stations/Data Acquisition/AS Data (Ulf Linquister)
__________________________________________________

The main item discussed was: how should AS data be stored
in Rinex ? Apparantly there were two basic opinions as summarized below:

JPL:    P1 P2 L1 L2            (+ set the SNR = 5)
Berne:     P2 L1 L2 C1

Note that both P1 and L1 are the regular C/A pseudorange and
carrier phase data types and that P2 and L2 are "synthetic"
P-code like observables made up of a combination of C/A and
X-correlated ranges and phases. In addition, P1 is identical to C1.

There were arguments raised by several people for and against the
two formats above, and I'll try to summarize below:

Pros:
JPL format:  Easy for reader for Rinex, since AS and non-AS data looks the
same. This simplifies the software when data from satellites
with AS and without AS are represented in the same time-tag (which
often happens when AS is on Block II satellites and not on Block I
satellites).
Berne format: The SNR information is not lost.

Cons:
JPL format: The SNR information is lost (set equal to 5 for AS data
and equal to 9 for P-code data).
Berne format: Requires a more complicated reader since data will located
in different places depending on if it is a Block I or II satellite. Also
the format is not consistent, since it treats P1 specially (sets it to
C1) and does nothing to L2 and P2 which are very different to their
P-code counterparts (L2 and P2).

The discussion was very lively and it was concluded that there was not
enough time to resolve this question during the Working Group meeting.
Therefore, Dave Starr, Werner Gurtner, Mark Caissy, and Miranda Chin voluntered
(or were voluntered) to come up with a modified Rinex format (Rinex III)
which was:
A) Backwards compatible with Rinex II and I
B) Resolves the problems outlined above with the two existing formats.
C) It was suggested that this issue be resolved as quickly as possible
to reduce confusion in the future (files from different analysis centers
would have the same data, but formatted differently and yet be labeled
as being Rinex).

The following action items are suggested:
1) The working group of 4 should produce a draft solution by the
Fall AGU for presentation to the IGS members at this meeting.
2) Final format should be agreed to by the Berne meeting in March, 93.

Other items discussed were: Station naming, receiver naming, antenna
naming, and antenna heights (with reference to the IGS Pilot Service).
The following Trimble and MiniMac naming conventions were supplied
by Miranda Chin:

Trimble:
-------

Receiver Type     Description
--------------    ----------------------------------------------------
Trimble 4000S     This includes 4000SL and 4000SX (single frequency)
Trimble 4000SD    This includes 4000SLD(dual freq. L2 squaring)
Trimble 4000ST    This includes 4000SST(dual freq. L1 c/a, L2 squaring or p)
Trimble 4000SE    This includes 4000SSE(dual freq. p-code on L1 and L2)

Antenna Type      Description
--------------    ----------------------------------------------
Geodetic L1       To use with Single frequency geodetic receiver
Geodetic L1/L2         "      Dual            "
Kinematic L1      antenna without a ground plane
Kinematic L1/L2              "

MiniMac
-------

Receiver Type     Antenna Type            Description
-------------     -------------------     -----------------------------
2816AT            Macrometer X-dipole     This system is used in CIGNET
2816              MiniMac patch           A field unit

The following conventions should be used for the Rogues:

Rogue
-----

Receiver Type     Antenna Type             Description
-------------     -----------------------  -----------------------------
SNR-8             Dorne-Margolin C146-6-1  2 unit rack-mounted (big Rogue)
SNR-800           Dorne-Margolin C146-6-1  1 unit rack-mounted (big Rogue)
SNR-8A            Dorne-Margolin C146-6-1  MiniRogue - not CONAN compatible
SNR-8C            Dorne-Margolin C146-6-1  MiniRogue - CONAN compatible
SNR-8000          Dorne-Margolin C146-6-1  TurboRogue

*******************************************************************************

Data Traffic and Communications (Peter Morgan)
______________________________________________

Peter presented overheads detailing the ability of the network to  carry
the  current  load  of  IGS traffic. He  explained  that  the  available
statistics  varied in quality from region to region with  some  regions,
notably  Europe  very reluctant to divulge the distribution  of  traffic
due to politcal nature of Europe.

Peter  commenced the discussion by showing the capacity of the  Internet
to carry data and then proceeded to some of the important nodes used  in
the  IGS  Campaign.  By far the most important node  is  the  node  that
services  CDDIS at Goddard. This node, at College Park,  which  services
the  traffic  to IGN in Europe to Australia and all USA  analysis  sites
except  JPL  and NGS was estimated to have a daily load near  1  million
TCP/IP  packets  per  day which accounted for 5 to  10  percent  of  all
traffic.  Network  utilization graphs were then shown for  slower  speed
networks into Australia. Peter showed the congestion on the Pacific link
to  Australia  where a single daily down load accounted for  5%  of  all
network  traffic. Line saturations became almost intollerable  when  the
capacity reached levels of 48 kbps.

Discussion
There was some discussion on the amount of extra and dulpicated data  on
the  network. Peter indicated that some of this duplication,  especially
that  into Australia, was necessary to monitor the status of the  netwok
and its ability to cope as he had better control of these links.

Peter expressed concern over the long term effect that unbounded  growth
of  CORE  stations might have on the netwok especially as  other  global
projects  went about emulating the IGS Campaign. He expressed  the  view
that it was essential for a network of efficient well supported regional
centers to be established.

*******************************************************************************

Analysis Center Coordination (Clyde Goad)
_________________________________________

Analysis Coordinator: Clyde Goad
                      The Ohio State University
                      Department of Geodetic Science and Surveying
                      1958 Neil Avenue
                      Columbus, Ohio 43210   USA

October 15-16, 1992  meeting at Goddard Space Flight Center

The Orbit

The representatives of the analysis centers plus the Coordinator met
at the Goddard Space Flight Center, October 16, 1992 (DOSE meeting week)
to discuss future activities and responsibilities.  The initial topic was
the identification of the orbit product(s) which users of the system would
utilize.  It was agreed that the product would continue to be a the usual
Cartesian elements (position coordinates) in the Earth centered, Earth
fixed frame.  The location will refer to the satellite's center of mass.
Velocities, clock offsets and drift estimates are supported by the SP3
format and can also be included at the discretion of each center.

Quality Control

A major product for individual analysis centers and users of the orbital
products could be plots of differences, but these are not easily
transmitted electronically.  Such products will be done by the analysis
center coordinator and distributed in hard copy form(reports).  Other
products which can be generated rather easily on a routine basis are
statistical values such as RMS differences, common rotations and trans-
lations between any two orbital products.  Such a program has been
developed at the University of Berne and implemented at Ohio State.
Shortly the weekly orbital products will be compared and reported
using the Berne software product.

The analysis center coordinator will continue to monitor the orbits using
the graphical techniques and report possible blunders to the individual
center.

Another quality control product will be a history of baseline
determinations between stations not participating in the orbital
reductions.  Several global baselines (the order of 5 or so) will be
chosen and reduced daily with each precise orbital product.  A statistical
report will then be generated.  Suspicious baseline recoveries will be
questioned within a short time after orbits are deposited in the data
base.

Another software check can be the recovery of orbital force model
parameter values using the orbital products directly.  Systematic
differences might be identified.

A Standard Product?

A standard product could be used by typical users of the orbits.  If one
such product does not exist, then the user must choose one of the
submitted orbits and thus might feel compelled to try them all in order
to assess for himself which on to use.  In the beginning this will
probably be done by many.  But in time, it could become burdensome. A
possible remedy would be to generate a weighted average of the contributed
orbits in a way similar to what is now done by the time and Earth rotation
services.  This idea will be investigated, but with caution.

*******************************************************************************

Management Issues (Ivan Mueller, Gerhard Beutler, from IGS Status Report No 7)
_____________________________________________________________________________

 - Let me briefly summarize the most important management/business matters
   discussed at the Goddard meeting, based on the working group report
   already delivered by Ivan I. Mueller (!) :

       The 1992 IGS Campaign officially ended 23 September 1992.
       As requested in the IGS Status Report of 14 September 1992 data
       collection and data analysis continued on an inofficial basis.
       Let me express the thanks of the Oversight Oommittee to all
       observatories, data centers, and analysis centers for making this
       possible.

       The IGS PILOT-SERVICE will start on 1 November 1992. This decision
       was taken unanimously. In the new undertaking the emphasis is on
       the SERVICE (showing up twice in the title), meaning that (a) a better
       adherence to standards on all levels has to be reached and that
       (b) the core and the fiducial network have to be completed.

       In this coordination tasks the Central Bureau and the Analysis Center
       Coordinator have to play important roles, the former concentrating
       on observational aspects, the latter on processing aspects. It is
       clear that these roles have to be based on the decisions taken in
       the working groups. In particular it is expected that a routine
       quality control for the orbits is set up by the analysis center
       coordinator for the period of the IGS PILOT SERVICE.

       Decisions concerning Epoch'92 :

          Bernard Minster was officially declared responsible as coordinator
          for Epoch'92 and for future similar experiments.

          It was recommended that the processing centers should reprocess
          the core data of Epoch'92 with the state of knowledge they have
          today. If this state did not change since the time they handled
          the Epoch'92 time slot for the first time, a reprocessing is
          not necessary. The IGS analysis center coordinator will come up
          with a suggestion for the official IGS orbit(s) for this time
          period.

          The Fiducial Network Plan will be provided by Bernard Minster.
          Future Epoch Campaigns will be organized, but only a regional
          and not a global coordination of such events will be required.

       Starting with 1 November 1992 there will be separate IGS mailboxes
       (a) for weekly reports plus related routine information, and (b) for
        messages of more general interest.  This service is provided by
       the University of Berne during the period of the PILOT SERVICE,
       it should be moved to the Central Bureau when the official IGS
       service starts.

       The IERS call for participation was (due 1 February 1993) was
       discussed in detail. The general opinion was that this issue
       should be discussed with the IERS Steering Board in view of
       the new situation created by the obvious success of the 1992
       IGS Test Campaign.

       There will be a business meeting of the oversight committee at the
       AGU Fall meeting, the most urgent agenda items will be

          Status of Epoch'92
          quality control issues
          Discussion of the IERS Call for Proposals

*******************************************************************************

Letter to IERS Steeering Board (Gerhard Beutler, sent out 19 November 1992)
___________________________________________________________________________

                                 Dr. Y. S. Yatskiv
                                 Chairman of the IERS Directing Board
                                 Main Astronomical Observatory
                                 Ukainian Academy of Sciences
                                 Kiev 252127
                                 U K R A I N E

Re : Call for Proposals for "GPS Participation in the IERS"

Dear Prof. Yatskiv,

In July 1992 the IERS Directing Board issued the Call for Proposals
for the "GPS Participation in the IERS" (based on the meeting of the
IERS Directing Board of May 1, 1992).  The proposals are due by
February 1993.  Simultaneously with and independently from these 1992
IERS activities the International GPS Geodynamics Service (IGS) 1992
Test Campaign took place (21 June - 23 September 1992).  Today we know
that this test campaign was a great success :  The scientific community
proved to be able to produce high accuracy orbits (sub-meter level),
and, what is important in this context, high accuracy earth rotation
parameters (pole coordinates x and y, length of day).  As a matter of
fact the campaign was so successful that the IGS Oversight Committee
decided on October 16, 1992 at its meeting in Goddard Space Flight
Center to start an  IGS Pilot Service on November 1,
1992.  This means that there will be an uninterrupted series of GPS
orbits and of earth rotation parameters starting with June 21, 1992.

These issues were discussed in length at the IGS Oversight Committee
meeting of October 15/16.  It was argued that in view of the expertise
and the tremenduous amount of work required in data collection,
transmission, and archiving, and, last but not least, in data analysis
- it can be expected that more or less the same institutions as those
collaborating under IGS will propose for the IERS (but presumably only
one will be accepted).  It was also argued that from today's state of
knowledge it would make sense to prepare a joint IGS proposal to IERS
representing all IGS participants.  Due to the fact that the IERS CFP
has already been distributed, nobody can stop individual institutions
now from writing proposals to IERS.  However an IGS proposal on top of
all these might be confusing and inappropriate, although probably the
best GPS coordinating center for the IERS would be the IGS Central
Bureau representing all IGS institutions jointly.

Thus the IERS will probably get several proposals from IGS
participants by February 1, 1993.  All of these institutions will
continue contributing to the IGS Pilot Service (and to the "final" IGS
later on), and therefore probably would like to see a collaboration on
a higher level between IERS and IGS.

In summary it can be stated that due to the 1992 IGS activities (3
months test campaign and Epoch '92) the situation considerably changed
since the IERS Call for Proposals was sent out. The IGS Oversight
Committee believes that a reexamination of the IERS-CFP-rationale by the
IERS Directing Board would be appropriate.

To facilitate progress we suggest the following action:

Between 24 - 27 March 1993 the 1993 IGS Workshop will take place at
the University of Berne. The IGS Oversight Committee and the IERS
Directing Board should coordinate their GPS activities at this
meeting :

 - The final IGS Proposal to IAG (due prior to the Bejing
   assembly) would only be written after a thorough discussion with
   the IERS Board (hopefully concluded with a formal agreement).  Part
   of this proposal would address the collaborative role of IGS in
   IERS.

 - The IERS Directing Board would wait with its selection of GPS
   partners until after the Berne meeting.

It would be ideal if a meeting of the full IERS Directing Board
and ourselves could be arranged at/after the Berne IGS workshop, and
the Board is
cordially invited to attend the workshop as well.  It is no problem to
organize meeting rooms for this purpose.

I hope that the procedure outlined above is attractive to the IERS
Directing Board and remain with kind regards

                                              Yours sincerely

                                              Gerhard Beutler
                                              Chairman
                                              IGS Oversight Committee

cc: Dr. Martine Feissel, Director IERS Central Bureau
    Prof. W. Torge, IAG President
    Members of the IGS Oversight Committee
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