[IGSMAIL-141] Minutes of Goddard Meeting 1992
Gerhard
Gerhard
Tue Dec 1 15:35:11 PST 1992
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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
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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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