Technical Development
Center News No.4
(International Earth Rotation Service
VLBI Technical Development Center News){ Special Issue for the iRiS '93 TOKYO {publishedbythe Communications Research Laboratoryin Tokyo, Japan
May, 1993(Reproduced in June, 1998)

Introduction

In October 1990, the International Earth Rotation Service (IERS) designated the Communications
Research Laboratory (CRL) and Haystack Observatory (in the United States) as Technical Development
Centers (TDC).
The Technical Development Centers are concerned withI. the development of new observation techniques and new systems for advanced Earth's rotation
observations by VLBI and other space techniques,
II. the promotion of research in Earth rotation by advanced methods in VLBI,andIII. the distribution of new VLBI technology.
The TDC meeting is held twice a year, including the special members from outside the CRL. Thecommittee is advised, concerning the plan of Technical Development by the special members. The Technical Development Center News is published biannually by the Communications Research Laboratory
to inform on current activities to the IERS community. From the second TDC news, we publish theTDC News only in English taking the international distribution into account.

The iRiS '93 Tokyo Workshop was held at CRL12IERS TDC News No.4on January 18-21, 1993.
At the IRIS Steering Committee held during the XX th IUGG General Assembly in Vienna in
1991, the workshop on VLBI in 1993 was suggested by Dr.W.Carter as a Coordinator of VLBI in
IERS. Since the Science and Technology Agency in Japan approved the budget for the workshop,
the Communications Research Laboratory hosted the iRiS '93 TOKYO (International Workshop forReference Frame Establishment and Technical Development in Space Geodesy). It was also supportedby the Geodetic Society of Japan.
In the workshop, 111 participants came from 9 countries including 28 researchers from foreign countries. In total, 64 papers were given including 4 poster contributions. In the plenary meeting after all
the sessions, the concluding discussion was made.
The regular TDC meeting to have been in February 1993 was canceled because of the workshop andCSTG IRIS committee.
Program of the workshop
(1)
(2)
(3)
(4)
(5)
(6)
(7)

Opening
Review Session
Technical Development Center
VLBI Technology
Laser Ranging and reference frame
GPS and reference frame
Terrestrial reference frame

(8)
(9)
(10)
(11)
(12)
(13)
(14)

Regional VLBI network
Southern hemisphereTime and earth rotation parameter
Celestial reference frame
IERS Standards
Plenary meeting for concluding discussion
Closing| Banquet |Proceedings of the workshop available

Proceedings were distributed to the participants after the workshop. The Proceedings of the Workshop are still available and are free. If interested in the proceedings, please contact us at the address on
the last page. Please understand quantities are limited.
IRIS Steering Committee of CSTG was held

IRIS Subcommision Meeting was held on January 22, 1993 during iRiS '93 Workshop at CRL, Tokyo,Japan.

3May 1993

Previous Mtg:Vienna, IUGG General Assembly

Participants:

Thomas Clark
Dennis McCarthy
Arthur Niell
Bob E. Schutz
James Campbell
Ye ShuhuaDavid JaunceyPeter MuCulloch
Zuheir Altamimi
Koichi Yokoyama
Daniel Rosenblatt
Taizoh Yoshino
Michito Imae
Shin'ichi Hama
Yukio Takahashi
Kosuke Heki
Bret Engelkemier(NASA/GSFC)(USNO)(Haystack Observatory)(CSR/Texas Univ.)(Bonn Univ.)(Shanghai Observatory)(COSSA)(Tasmania Univ.)(IGN)(NAO/Mizusawa)(Guest Scientist in NIED)(CRL)(CRL/Kashima)(CRL/Kashima)(CRL/Kashima)(CRL/Kashima)(Guest Scientist in CRL)

Agenda1.
2.
3.

Opening T. Yoshino. CRL
Regional Reports
IERS Technical Development Reports

NAVNET and IRIS-A are to be combined.
10m antenna was newly built at Mizusawa for IRIS-P.
1IRIS-S has been conducted monthly using 4 stations.
1Global observing campaign at common date in which observing
takes place at all stations is proposed.
1Recent activities of TDC are reported from both Haystack andCRL.

1
1

Concluding Discussion at the plenary meeting of theworkshop

Concluding discussion was summarized by Prof.J.Campbell, Dr.T.Yoshino and Prof.T.Sasao as follows.

Conclusions
The large number of substantial contributions presented by members of the di erent Japanese institutions involved in VLBI clearly expresses the strong commitment of the Japanese scienti c community
to use and further develop this technique for the bene t of astronomy, geodesy and geodynamics. Inaddition, participants from other parts of the world added their input on related topics, re ecting theclose cooperation that exist between the Japanese and the international research groups concerned withVLBI.
Only a choice of some of the items of special interest can be mentioned here:

1. Technical developments
At present, several VLBI data recording and correlation systems are in use and under development.
Among these a rst production model of the Japanese K4-system recorder and correlator (one baseline)

4

IERS TDC News No.4

was on display. On the side of the MkIII/MkIV-systems the plans for a considerable bandwidth upgrade
as well as an increase of recording density of two orders of magnitude were presented. In the discussions,the question of lack of compatibility between the systems raised great concern, because, in principle,
VLBI requires observations between all available stations for both astronomy and geodesy in order toexploit the full information content provided by this technique.
In the nal plenary discussion of the workshop it was decided that the IRIS subcommission set up
a working group to produce a memo on a possible solution to the compatibility problem. The working
group will consist mainly of the individuals directly concerned with the technical side and start byfacilitating the information exchange between the di erent groups involved.
The solution to the problem of compatibility may be to de ne a common interface between thedi erent playback units and the correlator in order to be able to handle di erent inputs with the same
correlator. Such a solution should not preclude further developments towards much higher data rates
and recording densities.
In conjunction with the main item of VLBI recording and correlation systems, a number of interesting
new technical developments were presented, such as antenna cluster observations, lunar transmitters fordelta-VLBI, space-VLBI, a ber-optics link and portable VLBI antennas.

2. Systematic e ects in VLBI observations
Several contributions dealt with the path delays in the atmosphere, but while in earlier meetings
the wet part of the neutral atmosphere was most prominent, this time the need for improved mapping
functions of the dry part was stressed. Mismodelling can introduce baseline length changes and may
distort global networks by several centimeters. The vertical component of the positions su er 3 to 6
times more from atmospheric modeling errors than the horizontal components.
Several contributions discussed the e ects of the ionosphere, both in terms of a nuisance e ect aswell as in view of providing information for monitoring the ionosphere.

3. Plate tectonics
Results from measurement series of more than eight years are yielding highly precise baseline rates
which can be compared to plate motion models derived from geophysical data. The emphasis is now
turning to those sites near the plate boundaries, where large discrepancies have been revealed and need
to be explained, such as in California, Alaska, Japan and eastern China.
The regional VLBI networks in Japan and in Europe, which became operational only a few years
ago, are already showing the rst signs of tectonically signi cant site motions.

4. Reference frames
A large section of the meeting was concerned with reference frames, both celestial and terrestrial.
The lack of uniform coverage at both levels became apparent in the southern hemisphere, althoughongoing campaigns are busy to close this de cit. The fact that several new stations are coming up
and are in the planning in South America (Santiago and Fortaleza) and on the continent of Antarctica(O'Higgins, Syowa and McMurdo) demonstrates the growing interest in using VLBI for astronomicaland geodynamical research in the southern hemisphere.
The importance of the VLBI contributions to the ITRF became apparent in many global solutions
and it was recommended to use the most recent ITRF-solutions when tying regional nets to the globalframe.
The increasing share of GPS in the establishment of the terrestrial reference frame was highlighted bycontributions about regional networks in the western Paci c. In this respect, the suggestion to structure

5May 1993

the di erent levels of ties between the networks by using the concept of GRL (Global/Regional/Local)
was seen as very useful.

5. Postglacial Uplift
In view of the diculties to achieve high accuracy in the vertical component of positions due toatmospheric delays, it was important to note that the smaller horizontal motions associated with thepostglacial uplift phenomenon might be easier to detect, because of the high accuracy of the baseline
lengths derived from the VLBI measurements.

6. Antarctic stations
Both the successes and the disappointments associated with the rst attempts to achieve geodetic
ties with the continent of Antarctica were demonstrated in the contributions on the new stations ofSyowa (Japan) and O'Higgins (Germany). While the German station is scheduled to be manned atleast twice per year and will participate in the southern VLBI campaigns, the station of Syowa and theplanned station of McMurdo (USA) have received no rm commitment yet to be operational for VLBI
in the future. In view of the tectonically unstable location of O'Higgins it will be very important tohave the two other sites included in the network, in order to be able to determine the plate motions ofAntarctica.
In a more general context it was pointed out that the commitment to regular observing campaigns
should not lag behind the technical developments.

J. Campbell
T. Yoshino
T. Sasao

Working Group on System Compatibility founded under
CSTG IRIS Subcommision

Since a serious compatibility problem between di erent VLBI recording and correlation systems(MkIII/IV, K-4 and S2/Canadian) was recognized, it was decided in the nal plenary discussion of theworkshop that the IRIS subcommission of the CSTG set up a working group to produce a memo on
possible solutions to the compatibility problem. The solution to the problem of compatibility may be tode ne a common interface between the di erent playback units and the correlator in order to be able tohandle di erent inputs with the same correlator. The working group consists of the individuals directly
concerned with the technical side and will start by facilitating the information exchange between thedi erent groups involved.
Possible solutions will be further discussed at the VLBI conference in Kyoto, Sept. 6-10, 1993.

6IERS TDC News No.4

The TDC News are published biannually. To begin or discontinue the receipt of the TDC News,
please send a message to the following address. Comments, questions and /or suggestions can be also
sent to the following address.
Taizoh Yoshino
IERS VLBI Technical Development Center
Communications Research Laboratory
Nukui-kitamachi 4-2-1
Koganei, 184 Tokyo
JAPAN(FAX)(MarkIII)(Internet)+81-423-27-6077
CRL
yosh@frex.cc.crl.go.jp

Kagami-biraki (Break open the barrelhead of a Sake barrel)
at the banquet of the iRiS '93.