Subject: [IGSMAIL-372] Time
From: Ruth Neilan
Date: 19 NOV 1993 20:04:52

IGS Electronic Mail       19-NOV-1993 20:04:52       Message Number 372
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From: Ruth Neilan 
Subj: Analysis Center Workshop
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                       Subject:                               Time:6:24 PM
  OFFICE MEMO          Analysis Center Workshop Summary   Date:11/18/93
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  Summary Recommendations of the Analysis Center Workshop 
                      October 12-14, 1993,
                     Ottawa, Ontario, Canada

      Submitted by the IGS Central Bureau (Neilan and Zumberge) and  
                 With assistance from Kouba and Beutler
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The IGS Analysis Center Workshop was held in Ottawa, Canada from October 
12-14.  It was hosted by Energy, Mines and Resources, an organization 
that includes both the Canadian Geodetic Survey (CGS) and the Geological 
Survey of Canada (GSC). 

The final session was chaired by G. Beutler, and included summaries of 
the workshop sections as well as recommendations.  The sessions of the 
workshop were organized in the following manner.  Position papers are in 
the final review process and will be distributed as hardcopy report.

1) PROCESSING STANDARDS, FORMATS, REPORTS
     G. Mader (facilitator), 
     J. Zumberge, C. Goad (position paper)

2) IGS ORBIT PRODUCTS
     B. Schutz (facilitator), 
     G. Beutler, J. Kouba, T. Springer (position paper)

3) IGS PROCESSING STANDARDS
     G. Blewitt, T. J. Martin Mur (facilitators)

4) INTEGRATION OF REGIONAL CLUSTERS/STATIONS, DISTRIBUTED PROCESSING
     J. Kouba, Y. Bock (facilitators)
     G. Blewitt, G. Gendt (position paper)
     Y. Bock (position paper to be incorporated into above)

============================================================
The following recommendations were adopted:

1) IGS PROCESSING STANDARDS/REPORTS/FORMATS (G. Mader)

IGS Products that Require Formats:
1a) Orbits
-     orbit format will contain SV clocks (either broadcast or precise) 
at same frequency as ephemeris

-     separate format for higher-frequency precise SV clocks (format to 
be determined, and to be applicable to station clocks)

-     SP3 will be the format of initial IGS orbit product; all Centers 
should supply beginning NO LATER THAN January 1994

-     work to begin on new orbit format, with possibility that orbits 
and clocks can coexist in same file at different frequencies

-     Zumberge to coordinate e-mail discussion on possible clock and 
orbit formats

1b) Earth Orientation:
-     IERS format (IGS mail message 10) for first six fields
-     differences in additional fields reported

1c) Summary Files

-     wide variation in content, style, ease of understanding, etc.
-     move to format and restructure some fields (e.g. comments) to 
enable easier scanning of files

1d) Conclusion on above issues
     Zumberge to coordinate preparation of EO and Summary File based on 
issues raised during discussion. Time frame, end of November - mid-
December.

1e) Stations for Global Analysis

-     Each of the following stations is currently used as a fiducial 
(coordinates are held fixed or tightly constrained) by a majority of 
Analysis Centers; data from sites denoted by * may be a concern in two 
ways: timeliness of data such as the DSN sites or discrepancies in the 
site tie information

     Algonquin Park
     Fairbanks
     Goldstone*
     Hartebeesthoek*
     Kokee Park
     Kootwijk
     Madrid*
     Santiago
     Tromso
     Tidbinbilla*
     Wettzell
     Yarragadee
     Yellowknife

-     Propose that coordinates of all of the above stations (with 
possible exception of the * sites) be fixed or tightly constrained by 
all Analysis Centers in their production of the orbit product.  

-     Propose that all Centers use the same set of coordinates and 
velocities for the above sites

2) IGS ORBIT PRODUCTS (G. Beutler)

2a) Decision 1: Two combined orbits will be generated based on 
principles developed in position paper

     - "Rapid Product" based on IERS Series A

     - "Archive Product" based on IERS Series B

     The generation of these will be the responsibility of the Analysis 
Center Coordinator

2b) Decision 2: Combined Solution will be generated when all Analysis 
Centers have submitted their products or within 2 weeks after the 
observations - whichever happens first

2c) Recommendations/suggestions to Analysis Coordinator:

     - base pre-analysis on orbit dynamics

     - base combined solution on average

     - stimulate further research for future improvements

2d) Governing Board should decide whether currently existing combined 
orbit products (pre-1994) ought to be distributed

3) IGS PROCESSING STANDARDS (G. Blewitt)

3a) First task is to gather information on Analysis Center models, 
Estimation Strategy, coordinates, etc.

     - Blewitt and Zumberge (CB) will develop an electronic 
questionnaire to be filled out by Analysis Centers, with the first 
questionnaire being a draft to ensure that all points of interest to all 
of the Analysis Centers are included.  (Central Bureau will assist.) 

     - completed questionnaires will be made available to all Centers, 
IGN/IERS, and will be available on the IGS Information system being 
implemented at the Central Bureau

     - will systematically document differences and changes

     - how does this relate to differences in solutions?

3b) Centers agreed in principle to adopt same set of fiducial 
coordinates for purposes of orbit/eop products

     - the proposed  list of stations is as above, in section 1, 
Stations for Global Analysis)

     - Centers will assess consistency by processing weeks 680 & 681

     - IGS Mail message 263 will be the standard for monument 
coordinates and antenna heights.

4) CONSIDERATIONS FOR (FUTURE) DISTRIBUTED PROCESSING (J. Kouba)

-     using IGS orbits is the simplest form of distributed processing

-     distributed processing should imply minimal computational increase 
for analysis centers

-     IGS should foster and encourage regional analyses (e.g. Associate 
Analysis Center, Governing Board representation, recommendations, 
reports, guidelines, etc.)

-     fiducial-free contributions from Analysis Centers will be 
necessary in the future and are encouraged as soon as is reasonable

-     additional products, e.g. tropospheric calibrations, may also be 
useful in distributed processing

-     additional research needed for distributed processing strategies 
(e.g. the effect of data overlaps)

Remarks Concerning "Integration of Regional Clusters/Stations" (G. 
Beutler)

There will be no changes in IGS Terms of Reference in the near future 
(certainly not prior to the Boulder IUGG General Assembly)

Important problems have to be addressed soon, including:
     (1)     A coordination effort between Analysis Centers would allow 
the processing of "all" upcoming "global" or "common" stations

     (2)     Regional Analysis Centers exist, more are being 
established.  IGS is interested in some of their sites, but proper 
incorporation into IGS network is necessary (e.g. observance of 
standards and procedures)

Within the definitions of the Terms of Reference:
    1)     Analysis centers fall into two categories; Analysis Centers 
and Associate Analysis Centers.

    2)     Associate Analysis Centers are organizations that produce 
unique products, e.g. ionosphere information or fiducial station 
coordinates and velocities within a certain geographic region. 
One may e.g. think of an new Associate Analysis Center with the main
task of combining station coordinates, velocities produced by other
agencies (Analysis Centers, Associate Analysis Centers and possible
processing agencies outside the IGS).