MIDTERM REPORT OF THE INTERNATIONAL VLBI SERVICE

FOR GEODESY AND ASTROMETRY (IVS)

Wolfgang Schlüter [1], Ed Himwich[2], Axel Nothnagel[3], Alan Whitney[4] and Nancy Vandenberg [2]

1. General Remarks

The IVS (International VLBI Service for Geodesy and Astrometry) was established in February 1999 in order to support VLBI programs for geodetic, geophysical and astrometric research and operational activities. IVS coordinates the observations, the data flow, the correlation, the data analysis and the technology developments.

IVS is recognized as a Service of the International Association of Geodesy (IAG) since July 1999 when the General Assembly was held in Birmingham/England and is also recognized as a Service of the IAU since the XXIVth General Assembly, Manchester/England, August 2000. Thus, acting within the frame of IAG and IAU, IVS has to guarantee provision of the required results on a regular and timely basis. Nowadays the IVS is a Technique Center for the International Earth Rotation Service (IERS) and has close interactions with IERS. The VLBI technique uniquely provides the parameters for the CRF and is the only technique to determine the celestial pole. IVS is producing Earth Orientation Parameters (EOP) from 24h observation sessions regularly and periodically carried out such as NEOS and IRIS. The parameters in particular are the celestial pole coordinates dj, de polar motion parameter xp, yp, and DUT1. In addition DUT1 is derived from 2h observation sessions carried out quasi daily by Wettzell and Green Bank, nowadays Wettzell and Kokee Park. CRF solutions are regularly derived in order to determine quasar positions or to detect proper motions of quasars. Station positions and velocities are derived from all the observations and are a strong contribution to the ITRF. It is planned to provide EOP with subdaily resolution and baseline length evolutions. The products are available via data centers at NASA GSFC/Greenbelt, USA ftp://cddisa.gsfc.nasa.gov or BKG-Leipzig, Germany ftp://ftp.leipzig.ifag.de or Observatoire Paris, France ftp://ivsopar.obspm.fr. Access to IVS Homepage is available via http://ivscc.gsfc.nasa.gov/ mirrored at BKG http://www.leipzig.ifag.de/IVS and CRL http://ivs.crl.go.jp/mirror

2.  Summary of the IVS Components

 A Call for Participation was released jointly by CSTG and IERS on June 1, 1998. The proposals were evaluated and accepted by the Steering Committee. In summary IVS has today

 All together there are 77 components representing 30 Member Organizations in 15 countries and more than 230 individual Associate Members. IVS has 31 Member organizations, and 6 Affiliated Member organizations.

Fig. 1. Overview of the distribution of the IVS components

3.  IVS Activities

 The 1^st Directing Board meeting was held in Wettzell on February 11, 1999 in order to establish the Service and to initiate activities under the flag of the IVS. As of the inauguration date of IVS, on March 1, 1999, its web site was available at http://ivs.gsfc.nasa.gov.

Soon thereafter, a solicitation for IVS data and analysis was released to obtain proposals from the Operation and Analysis Centers on the provision of products such as correlation results, EOPs, and combined analysis. Those products derived by the Analysis Centers were designed to become “official” IVS products. In the same solicitation the call for an Analysis Coordinator was released.

The IVS Annual Report 1999 was published in August 1999 (electronically) and September 1999 (printed) [1]. The intention of the Analysis Report was to provide a document on the status of all components. A procedure was created to standardize the layout, which supported and accelerated the publication of the Annual Report 1999.

The 2000 IVS General Meeting was organized and held in Kötzting, Germany, during February 21-24, 2000. It was a successful meeting with more than 120 participants registered. The goals of the meeting were determined by a program committee. The main character of the 1^st General Meeting was addressed towards young researchers. Overview talks and tutorials were held before the sessions, in order to introduce the session topic to those who work in different areas. It has to be mentioned that the proceedings of 2000 IVS General Meeting [2] were published in June 2000. The proceedings published nearly all the papers and tutorials and are a very valuable tool, especially for people starting to work in VLBI.

At the 3^rd Directing Board Meeting, held in Wettzell before the General Meeting, slight modifications to the Terms of References were made in order to clarify the status of the Analysis Centers and to include Affiliated Members. Affiliated Members will be informed about IVS activities without having obligations to IVS.

During the IVS 2000 General Meeting, a first meeting was held of the IVS Working group on "GPS phase centers Mapping" , which is a joint Working Group of the International GPS Service (IGS) and International Laser Ranging Service (ILRS). The objectives were "to study the feasibility equipment, time required, and if it could be done with accuracy sufficient to make it worthwhile". The members of the WG are Brian Corey/ MIT-Haystack, Ed Himwich/NVI, Inc./GSFC for the IVS, Tom Herring/MIT-Boston, Tim Springer/AIUB for the IGS and Graham Appleby/ and Richard Biancale/CNES for the ILRS. The activity and the status of the work could be seen on the IVS-homepage http://ivs.gsfc.nasa.gov.

On the last day of the 2000 General Meeting, February 24, the first Analysis Workshop has been held. Axel Nothnagel, who became IVS Analysis Coordinator on October 1, 1999, invited to the meeting. Standards, analysis models and contributions of the various Analysis Centers were discussed, five Working groups have been established in order to share the workload. Access to all the information is made available via http://ivs.gsfc.nasa.gov and its link to the Analysis Coordinator homepage.

A regular combination procedure for the VLBI derived EOP series, provided from the four Analysis Centers, NASA Goddard Space Flight Center/Greenbelt, USA, Bundesamt fuer Kartographie und Geodäsie/Leipzig, Germany, Institut for Applied Astronomie /St. Petersburg, Russia and University of St. Petersburg, Russia has been developed by Axel Nothnagel and Christoph Steinforth of the Geodetic Institute of the University of Bonn. The combined results have been released as IVS products and are now used from IERS for further combination with the other techniques.

In 2000 the first Analysis Pilot Project has been started by the Analysis Coordinator in order to encourage more Analysis Centers to perform data analysis. A common set of data covering a period of one year has been released for the pilot project which allows to compare the results of the individual analyses, to unify the data reduction procedures and to exchange experience. In addition to the 4 global Analysis Centers, 9 more Analysis Centers participated in the Pilot Project. 17 different solutions have been derived using 6 different analysis software packages. The results have been discussed at the Second VLBI Analysis Workshop held at the Goddard Space Flight Center/Greenbelt, USA in the period from February 12-14, 2001. These activities are very encouraging and a second pilot project is going to be started soon.

In September 2000 the hardware VLBI Standard Interface (VSI-H) specification has been released (more detailed information: http://ivs.gsfc.nasa.gov). VSI-H specification was developed by an international committee of experts in VLBI instrumentation, led by Alan Whitney/MIT-Haystack, IVS Technology Coordinator, in a concerted effort to standardize interfaces to/from VLBI data recording and playback systems. Adherence to the VSI-H specification will allow data collected on heterogeneous VLBI data systems to be processed directly on VLBI correlators. A standardized software interface, VSI-S, is expected to follow within the next year. Thanks to the committee especially Alan Whitney/MIT-Haystack-USA as the chair, Wayne Cannon and Richard Worsfold/CRESTech-Canada, Ralph Spencer/ Jodrell Bank Observatory-UK, Richard Ferris/CSIRO Telescope National Facility-Australia, John Romney, George Peck/NRAO-USA, Brent Carlson/Herzberg Institut of Astrophysics NRCC-Canada, Tetsuro Kondo, Junichi Nakajima, Yasuhiro Koyama, Mamorou Sekido and Hitoshi Kiuchi/CRL-Japan and Mickael Popov/Astro Space Center of Lebedev Physical Institute Moscow-Russia the specification have been set up in a short period of time with a broad international acceptance.

The 4^th Directing Board meeting was held on September 17, 2001 in Paris-F and the 5^th Directing Board Meeting was held in Greenbelt-USA. In order to improve the IVS products and to optimize the resources within IVS a Working Group for the evaluation of the existing observing programs was created with the following task :

·         Review the usefulness and appropriateness of the current definition of IVS products and suggest modifications.

·         Recommend guidelines for accuracy, timeliness, and redundancy of products.

·         Review the quality and appropriateness of existing observing programs with respect to the desired products.

·         Suggest a realistic set of observing programs which should result in achieving the desired products, taking into account existing agency programs.

·         Set goals for improvements in IVS products and suggest how these may possibly be achieved in the future.

·         Present a written report to the IVS Directing Board at its next meeting.

 Harald Schuh is the chair of this group and experienced members are invited to contribute.

The First IVS Technology and Operations Workshop (TOW) was held at Haystack Observatory during March 12-14, 2001. The program committee for the meeting was lead by Ed Himwich, NVI Inc/GSFC. The workshop provided detailed training on VLBI technology and operations and was attended by over 60 people. This meeting will be repeated every two years. The material covered was adapted to meet people's interests as well as important issues. A notebook covering details of the training sessions and talks were provided to all attendees. This notebook should prove to be useful a reference for all involved.

4. Personal fluctuations in the Directing Board

Some personal fluctuations in the Directing Board (DB) have to be mentioned. The representative of the IAG, Gerhard Beutler, when he was elected as Vice President of IAG, withdrew from the board after the 2^nd DB meeting, held in Birmingham, July 19, 1999. He was the initiator of the IVS and we have to express our thanks to him. James Campbell, one of the most experienced VLBI experts, was nominated by IAG to be the new IAG representative. Axel Nothnagel, representing the Analysis Centers on the DB, started his work as Analysis Coordinator (AC) as of October 1, 1999. Up to October, 1999 the function of the AC was jointly carried out by Marshall Eubanks, Chopo Ma and Nancy Vandenberg. Marshall Eubanks, representative of the Operations Centers and Correlators, has founded a new e-business, which demands his full attention. He withdrew from the DB and was replaced by Kerry Kingham.

In accordance with the ToR, elections have carried out for the positions of the Analysis and Data Center representative and of the Technology Development Center representative. Both positions have been occupied for the first two years term only, starting at the initiation date of the IVS. Since Axel Nothnagel became the Analysis Coordinator in October 1999 the position of the Analysis Representative became vacant. The position of the representative for the Technology Development Centers was held by Tesuro Kondo, CRL-Japan. In addition one of the At Large positions, that position held by Wayne Cannon, was set for a two years term only. The election has been held in December 2000. Harald Schuh, Austria was elected as the representative for the Analysis and Data Centers, Arthur Neill, USA was elected to represent the Technology Development Centers and Yasuhiro Koyama, Japan was elected as AT Large Member. After the election, it turns out that the Directing Board is strongly dominated by US and European representatives and improvements for the balance of representatives from different agencies, nations and groups have been discussed at the 5^th Directing Board meeting. The enlargement of the board by a 3^rd At Large Member was decided and the ToR have been modified.

The current members of the DB and their functions are:

Ex Officio:

Coordinators:  

Representatives:  

Literature 

[1] Vandenberg, N.R. (editor): Annual Report 1999, NASA/TP-1999-209243, Greenbelt-MD, August,1999
[2] Vandenberg, N.R. and Baver K.D. (editors), 2000 General Meeting Proceedings February 21-24, 2000 Kötzting, NASA/CP – 2000 – 209893, Greenbelt MD, June 2000

[1]Bundesamt für Kartographie und Geodäsie, Fundamentalstation Wettzell, D-93444 Kötzting, Germany
[2] NVI, Inc./NASA Goddard Space Flight Center, Code 920.1, Greenbelt, MD 20771,USA
[3] Geodätisches Institut, Universität Bonn, Nussallee 17, D-53115 Bonn, Germany
[4] MIT-Haystack Observatory, Off Route 40, Westford, MA 01886-1299, USA

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