• Upcoming Meetings
• GGP Meeting, 8 May 1996, EGS The Hague, Netherlands
• GGP Data Center
• Proposition of ICET as the GGP Data Center
• Closing Remarks
• Questionnaire on GGP Pilot Study and Observing Periods

Upcoming Meetings

(1) The will be a GGP Business Meeting at the International Symposium on Gravity, Geoid and Marine Geodesy in Tokyo, to be held at the University of Tokyo on Wednesday, 2 October 1996, Sanjo Hall (B1 Floor), 12:15-13:15. The meeting is being organized by Shuzo Takemoto (takemoto@kugi.kyoto-u.ac.jp). The purpose of the meeting is to review plans for the upcoming start of the GGP Observing Period (see below).

(2) There will be a combined meeting of Working Group 5 of the Earth Tide Commission and Working Group 7 of the IAG International Gravity Commission project "Global Gravity Monitoring Network" at the University of Tokyo on the evening of 3 October. Time and location have not yet been announced.

The meeting is being organized by Bernd Richter (richter@ifag.de). The purpose of the meeting is to discuss the present status of high quality absolute gravity networks, particularly where AGs and SGs can be used in combination to improve gravity determination and site characterization.

(3) There will be GGP-related discussions at the Working Group Meeting - High Precision Tidal Data Analysis in Bonn, 16-19 September 1996. At this meeting the Theoretical Tidal Model and other traditional issues will be discussed. The meeting is organized by Manfred Bonatz and Gerhard Jentzsch (jentzsch@ifg.tu-Clausthal.de)

(4) There will be a Chapman Conference on Microgal Gravimetry: Instruments, Observations and Applications in St. Augustine, Florida, 3-6 March 1997. The Conveners are Bill Carter (bcarter@ce.ufl.edu), Glenn Sasagawa (sasagawa@creep.colorado.edu) and Bernd Richter (richter@ifag.de). The purpose of the meeting is to discuss aspects of AG and SG design and applications. Further details can be found in EOS (26 July 1996) or through the AGU (http://www.agu.org).

GGP Meeting, 8 May 1996, EGS The Hague, Netherlands

A short informal business meeting was held at the EGS to review the status of GGP stations. In attendance were (from memory, where are your Minutes, Jacques?): D. Crossley, J. Hinderer, Jussi Kääriäinen and Henri Virtanen, Jürgen Neuberg and Peter Schwintzer, Corinna Kroner. Due to the lateness of the notice for the meeting, the fault of procrastination by the GGP Chairman, it was not possible to have a full discussion. Nevertheless, a number of developments were noted:

• French and Chinese instrument upgrades are finished or planned respectively.
• GWR has finished the design and testing of a new vertically oriented double-sphere SG that promises to eliminate instrumentally-derived differences due to sphere properties. GWR Has also designed a new long-hold dewar. I do not have details of these developments; no doubt some of you know more.
• The recent installations in Metsahövi and Membach are working well.
• The Austrians are reported as having an instrument. Does anyone know who is in charge of this? Thanks to Bernard Ducarme I have the information (see the mailing list).

Discussions at the meeting centered around the timing of the start of the Observing Period. Due to the lack of communication between groups, it was suggested that the official start of GGP be delayed until the Earth Tides Meeting in Brussels next July. A convenient (calendar-wise) starting date would therefore seem to be 1 July 1997 for the start of the GGP Observing Period. This is the last and absolutely final delay we will have in starting the GGP.

Nevertheless, due to the excellent work being done by some of the groups in preparing instruments for the GGP, we (i.e. those present at the meeting) would like to suggest to the community that the period leading up to the official start of the GGP be designated as a Pilot Study Period to test the issues of data format, exchange and pre-processing of GGP data. This Pilot Study Period can be considered to be now in effect until 1 July 1997 provided SG groups are in agreement that this is a good idea.

I would therefore ask that you all return to me, by email or fax, replies to the short Questionnaire attached.

The final item of business was discussion about the GGP Data Center, as follows.

GGP Data Center

From the beginning of GGP, the community has argued about the need, purpose and organization of a Data Center. We all know the pros and cons very well and it is not necessary to review them here. However, a recent proposal has been received from ICET that I wish to present to you. My own feeling is positive, because Olivier Francis assures us that ICET will respect the terms of GGP Data Collection and Distribution that we have so long discussed at previous meetings.

Furthermore, ICET preserves the GGP Data at a place we all know well and within the community that most SG groups are part of (i.e. Earth Tides). There are not the disadvantages of GGP data being lost in a larger organization. Furthermore ICET, in spite of all the well-known discussions about its processing practices, now appears to have the computer power and (hopefully) manpower to deal even with GGP raw data (and we know how much that is!).

I now present to you ICET's proposal, which you can comment upon in the questionnaire.

Proposition of ICET as the GGP Data Center

As World Data Center:

-ICET is willing to collect, archive and distribute all available measurements of Earth tides (including gravity data).
-The adopted data format for data exchange is the PRETERNA format.
-ICET accepts 10-second, minute and hourly data.
-All the necessary information (calibration factor, station coordinates, pressure data,...) to process the data should also be transmitted to the Center.
-ICET can delay free access to data to the scientific community for a limited time duration (according to the GGP requirement).
-ICET will regulate the access to the data to authorized GGP members. The data will be put on line to a dedicated server accessible only by GGP members and only on request (by e-mail for example) for security reasons.

As FAGS service:

-ICET will archive the data on CD-ROMS and distribute them to the GGP members at regular intervals.
-ICET will perform Earth tide analysis of all the 1-minute pre-processed data sent to the Center on a regular basis. The results of the Earth tidal analyses will be automatically included in the ICET Data Bank.
-The raw data will be processed to produce 1 minute files within a year of their reception and then made available to GGP members.
-ICET will provide ocean loading vectors for all the available global ocean tides models.

O. Francis, Vice-Director of ICET
B. Ducarme, Director of ICET

End of ICET Proposition

Closing Remarks

It will be quickly obvious that the ICET proposal includes most of the right ingredients, but not all. To a large extent, that is because several issues are still not finally clarified, such as what constitutes raw data (1s, 10s or simply as recorded) and who is prepared to do the pre-processing and to what standards. However we should discuss these issues again in Tokyo.

From the point of view of the GGP Management, I intend to set up a GGP WEB Page at Saint Louis University, incorporating many of the suggestions that have been made regarding the publicity and dissemination of important information concerning GGP. Progress hopefully will be obvious by the Fall.

The GGP community is changing with the closure of some stations, emergence and movement of others and developments in funding (both up and down). For example we have been notified of the movement of one Japanese SG to Indonesia and the possibility of a second collaborative project between Japan and Kurt Lambeck in Australia. Gerhard Jentzsch also has plans for a German instrument south of the equator.

This circular is being distributed to all members of the GGP Mailing List, including potentially new members. If you wish to have your name added/deleted or can suggest others who might receive this Newsletter, please let me know.

I look forward to your replies and in finally getting GGP underway, as originally planned. Thank you for your patience.

David Crossley, GGP Chairman
St. Louis, September 14, 1997

P.S. I will be away until 16 August.

QUESTIONNAIRE ON GGP PILOT STUDY AND OBSERVING PERIODS

Pilot Study Period: Now - 97/7/1 Observing Period: 97/7/1 - 03/6/30

Name:

Organization:

SG Instrument(s) Location:

Contact (email, fax):

Question 1: Will you have one (or more) functioning SGs at the start of GGP Observing Period?

Question 2: Do you agree with the time periods for the Pilot Study and Observing Periods?

Question 3: Will you contribute data to GGP within the required time after the start of the Observing Period?

Question 4: Will you be able to provide GGP Data, in the format stipulated (Crossley and Hinderer, 1996), via INTERNET directories? If not, please explain or describe your intentions.

Question 5: Are you in favor of ICET as the GGP Data Center? If not, what is your preferred alternative?

Question 6: Do you have further suggestions for GGP at the present time?

Return to D. Crossley by email (crossley@eas.slu.edu) or fax (+1-314-977-3117).