TECHNICAL DEVELOPMENT CENTER NEWS No.10
International Earth Rotation Service - VLBI Technical Development Center News

published by

Communications Research Laboratory
4-2-1 Nukui-kita, Koganei, Tokyo 184, JapanCOMMUNICATIONS RESEARCH LABORATORY

Serial No. 10
April 9, 1998

May 1997

CONTENTS
Overview of the Tenth TDC Meeting : : : : :: : : : : : : : : : : :: : : : : : : : : : : :: : : : : : : : : : : : :: : : : : : : : : : : :: : 2
Report of the Technical Workshop for APT and APSG in 1996 (TWAA96) : :: : : : : : : : : : : 6
Technical Reports
Recent Status of the Key Stone Project VLBI System :: : : : : : : : : : : : :: : : : : : : : : : : :: : : : : : : 8
The Multimedia Virtual Laboratory (MVL) and
Its Application to Cooperative Research : : : : : : : : : : :: : : : : : : : : : : :: : : : : : : : : : : :: : : : : : : : : : 13
Overview of Development of High-speed VLBI Terminal
and the Compatibility of VLBI Terminals : : : : : :: : : : : : : : : : : :: : : : : : : : : : : :: : : : : : : : : : : :: 15
Plan for a High-rate Data Recorder and a New Data Acquisition Terminal : : : : : : : : : 19
Next Generation VLBI Terminals (Should be) Planned at CRL : :: : : : : : : : : : : :: : : : : : : : 21
Preliminary Experiments of Radio Interferometer Using Fiberoptic Links
Modulated in radio Frequency : : : : : : : : : : :: : : : : : : : : : : :: : : : : : : : : : : :: : : : : : : : : : : :: : : : : : : : : 22
E ects of Precession and Nutation on Short (a few Hours) VLBI Experiments : : :: : 25
GSI's New Correlation Processing System : : : :: : : : : : : : : : : : :: : : : : : : : : : : :: : : : : : : : : : : :: : : : : 27

1

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IERS TDC News No.10

Overview of the Tenth TDC Kuniaki Uchida, the director of IERS TDC at
Communications Research Lab., opened the meetMeetinging.
Tetsuro Kondo (kondo@crl.go.jp)
Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314, Japan

2. Activity Reports of Each Organization by
the Special Members

The special members reported on the current
status of the activities of their organizations.

The tenth meeting of the Technical Develop- Geographical Survey Institute (Mikio Tobita)
ment Center was held on March 14, 1997 at the
Kashima Space Research Center of Communica- Mikio Tobita reported geodetic project at AsiaPaci c area in which GSI is involved.
tions Research Laboratory.
The second meeting of the Permanent Committee on GIS infrastructure for Asia and the Paci carea was held in Sydney, Australia in October,
Attendance
1996.
At this meeting it was proposed that geodetic
observation should be carried out in October, 1997
CRL members
using xed space geodetic stations available. Theof these observations is to establish precise
Kuniaki Uchida, Taizoh Yoshino, Shin'ichi Hama, purpose
geodetic
points in Asia Paci c area. In
Hitoshi Kiuchi, Akihiro Kaneko, Hiroo Kuni- particularreferenceco-locationof di erent techniques andmori, Chihiro Miki, Jun Amagai, Kohichi Se- local tie observations must
be carried out. It isbata, Hideyuki Nojiri, Toshimichi Otsubo, Yuko expected that 6 VLBI stations,16-20 SLR staHanado, Fujinobu Takahashi (KSRC: Kashima tions, 20 DORIS stations, 6 PRARE
stations andSpace Research Center), Yukio Takahashi (KSRC), more than 50 GPS stations will participate
in thisRyuichi Ichikawa (KSRC), Yasuhiro Koyama project. As for VLBI observations, they areex(KSRC), Mamoru Sekido (KSRC), Junichi Naka- pected to be the Fairbanks, Hobart, GSI-Kashima,
jima (KSRC), Eiji Kawai (KSRC), Tetsuro Kondo Kokee, Shanghai and Urumqi stations. Observa(KSRC)
tion schedule will be prepared by Shanghai usinga SKED program. Correlation processing will be
carried out by GSFC. Baseline analysis and distriSpecial members
bution of data will be carried out by Shangahi.
Nobuyuki Kawano (National Astronomical Observatory), Mikio Tobita (Geographical Survey Insti- National Astronomical Observatory (Nobuyukitute), Masayuki Fujita (Hydrographic Department, Kawano)
Maritime Safety Agency)
Following special members could not attend: Nobuyuki Kawano reported current status andNoriyuki Kawaguchi (National Astronomical Ob- future
plan of the National Astronomical Observaservatory), Kosuke Heki (National Astronomical tory (NAO).
Observatory), Kazuo Shibuya (National Institute The second stage of future plan will start fromof Polar Research), Hisashi Hirabayashi (Institute the 10th anniversary of NAO (next year). Reof Space and Astronautical Science), Yoshimitsu organization on a fairly large scale is also planned.
Okada( National Research Institute for Science and A review of NAO by outsiders has already begun.
Disaster Prevention), Teruyuki Kato (Earthquake The VLBI and VSOP projects has already comResearch Institute, University of Tokyo),pleted the rst stage review process by domestic
reviewers.
A VSOP satellite was successfully launched on
Minutes
February 12, 1997. A main dish antenna was also
successfully deployed.
Budgetary request for VERA (VLBI ExplorationofRadio Astrometry) for the scal year 1998 will be
1. Opening Greeting
proposed to the Ministry of Finance. The numberof antennas has been reduced from two antennas

May 19973

at each site to one. Investigation of dark matter is Daily observations on the full network (4 stations: Kashima, Koganei, Miura, and Tateyama) haveadded to the purposes of the project.
In collaboration with ISAS and NASDA, a RISE been carried out since September, 1996. Recently
satellite will be launched in 2003 using a HII-A the success rate for baseline analysis of the daily
observations has become nearly a hundred percent.
rocket.
NIPR (National Institute of Polar Research) is So far the results of baseline analyses can be anpromoting an Antarctic VLBI project. Equipments nounced at the latest within one and a half day afnecessary for VLBI will be shipped to Syowa Sta- ter daily observation (00:00-05:00 JST) is nished.
tion, Antarctica this year (Nov. 1997) by the 39th Kashima station had a problem with an air condiJapanese Antarctic Research Expedition (JARE- tioner in a receiver room, and this makes a baseline
39).
analysis result much worse. However, accuracy of
result was improved drastically by stopping operaHydrographic Department, Maritime Safety tion of air conditioner temporarily. Present accuracy (formal error) is 2 mm in baseline length forAgency (Masayuki Fujita)
a 2 MHz video frequency width observation.
Masayuki Fujita reported on geodetic observa- As for unmanned operation at remote stations ittions by the Hydrographic Department, Maritime is important how fast we can recover a system fromany trouble. Koyama said, \We could make it in 3
Safety Agency.
The rst round of measurements of rst-order days for the most inconvenient station, Tateyama."
control points using a mobile SLR system were Q: Why is accuracy improved by stopping air
completed last scal year (FY1995). The second conditioner operation?
round of measurements started, and a Chichijima A: An air conditioner in a receiver room in an anIsland point was measured from September to De- tenna at Kashima has a problem. When it works,
cember, 1996. Ishigakijima Island position will be room temperature changes periodically with a period of about 20 minutes with temperature amplimeasured from July to November, 1997.
A xed SLR system at Shimosato has been oper- tude of about 3 degree Celsius. This results inated since 1982. Current accuracy of the system is a fast apparent clock change dicult to remove.
about 3-4 cm. Fujita said that he wants to improve When the air conditioner is stopped, room temit to 1 cm. Initially the photo-detection system will perature change becomes more gradual. Consequently the apparent clock change becomes estibe upgraded.
Continuous GPS measurements (24 hours a day) matable. This may improve an accuracy in theanalysis.
are carried out in the Kanto area.
A D-GPS (1.5-2 m accuracy) system developedby the Aids to Navigation Department is prepar- 4.2. Current Status of KSP SLR System
ing its routine service. About 30 reference sites will (Hiroo Kunimori)be established by 1999. The Hydrographic Depart- Hiroo Kunimori reported on the current status
ment plans to make geodetic observations using ref- of SLR system in the KSP as follows.
erence D-GPS sites.
Kashima and Koganei SLR stations made an engineering level test observation on January 29 3. Report on TWAA96 (Yukio Takahashi)
February 14, 1997. The purpose of this test observation
is to evaluate the total operational ow
Yukio Takahashi reported on TWAA96 (Techni- from an observation
to an analysis and to detercal Workshop for APT and APSG 1996) held in mine any problems. Return
were detected
Kashima on December 10-13, 1996. See page 6 for for more than 40 passes bothsignals
atKashimaand Kodetails.
ganei. Single-shot rms value of the uncertainty inmeasured distance was 10-25 mm for LAGEOS and
4. Technological Development Reports
its variation within a pass was large. The normal
point rms value was 3-8 mm. Stability of groundtarget was 65 mm for 7 days. None of these values
4.1. Current Status of Key Stone Project meets the speci cation for the system. To satisfy(Crustal Deformation Observation System the speci cations both hardware and software willin the Tokyo Metropolitan Area) (Yasuhiro be upgraded and an engineering level test will be
continued.
Koyama)Yasuhiro Koyama reported on the current status 4.3. Multimedia Virtual Laboratory | Its
of KSP VLBI as follows.
Application to VLBI (Shin'ichi Hama)

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IERS TDC News No.10

Shin'ichi Hama reported on the Multimedia Vir- that an open-reel-type recorder is quite di erent
tual Laboratory (MVL) project, in particular em- from an cassette-tape-type one equipped with a hephasised in applications for VLBI use. The con- lical scanning head. Hence we only think about
cept of the MVL was proposed by the Telecommu- minimum compatibility between them when a new
nications Technology Council, in consideration of recorder is developed.
recent technological developments in telecommuni- Q: How about supply of tape? Is it easy to getcations. At present there is no uni ed idea about at reasonable prices?
MVL. Concerning VLBI applications, joint owner- A: Yes. GBR-1000 itself is used at commercial
ship of huge amount of data is attractive to provide TV stations. There is no problem concerning supgood prospect for a distributed analysis system and ply and price of tape.
for a virtual big antenna (see page 13 for details). C: Even though it is dicult to do radio astronQ: Image of MVL is obscure. Is it to use a remote omy as a main objective at CRL because it canlaboratory and to perform some experiment in an not be an ocial goal right now, please proceedwith the development of a millimeter wave lengthoce without going to the site?
A: Each person has his own idea. Some merely technology.
considers the MVL as an extension of the current
TV conference system. As for VLBI, it is consid- 5.3. Development of High Density Recorderered as a way to transfer a huge amount of data as an Expansion of K-4 Recorder (Hitoshi Kiwith fast speed.
C: At GSI we are thinking about possibilities uchi)
of applying MVL for circulation of remote sensing Hitoshi Kiuch reported on plans for high density
data. It will be of great help for distribution of recorder development. In his presentation he eminformation to the public.
phasized the following points. What TDC should
do is to contribute system development to realize a
5. Discussion About Signi cance of Devel- high accuracy measurement. However developmentin the CRL is not a satisfactory condition at theopment of Gigabit Recorder at CRL
present time. Development of VLBI system so far
never exceeds but merely follows those in USA. To
5.1 Overview of Development of Next Gen- overcome this situation we should develop a higheration VLBI Terminals and Their Compat- density recorder with a data rate of 2048 Mbps (64Mbps 2 32 ch or 128 Mbps 2 16 ch) dedicated toibility (Yukio Takahashi)
geodetic VLBI. There are good prospects for reYukio Takahashi reviewed all types of VLBI ter- alizing a video converter with a video bandwidth
minals currently used in the world. He also sum- wider than 64 MHz. As for the recorder, there
marized their compatibility and their accuracy in are thought to be no technical barriers for developbaseline analyses. Details are reported in this issue ment.
Q: What is the di erence between GBR-1000 and(see page 15).
this system?
A: Target is di erent. GBR-1000 is dedicated to
5.2 Current Status of Development of Giga- a radio
astronomy, while this system is mainly for
bit Recorder at CRL (Junichi Nakajima)
precise geodetic applications.
Existence of two types of recorder is not happy
Junichi Nkajima reported on the current devel- forC:users.
opment status of Gigabit Recorder (GBR-1000) introduced in the last TDC news (VLBI TDC News
CRL, No.9, pp.17-18, 1996). In addition to the 5.4 Perspective Image of Next Generation
report, he proposed the establishment of \domes- VLBI Terminal (Tetsuro Kondo)
tic next generation VLBI development team" aiming to develop a millimeter wave length wide band Tetsuro Kondo presented his expectations conVLBI technique on the basis of a bottom-up ap- cerning the development of the next-generation
proach (not top-down one). He also stressed that VLBI terminal. In his presentation he summaCRL should return to its starting point (or spirit) rized ideal feedback loop structures in the relawhen K3 VLBI system was developed. Namely tion between technical development and scienti c
CRL should be a user as well as a developer of progress into following two categories. One is an
VLBI technology. A plan and a developed tech- \improve accuracy" pursuit loop. In this feedback
nology should be announced world-wide. As for loop, observation system is designed to achieve thethe development of recorder, we should recognize best measurement accuracy from a technical point

May 1997

5of view. Cost-e ectiveness is sometimes regarded accuracy of measurements is sacri ced, widely disas an unimportant factor in system development. tributed terminals in case of VLBI will give a new
Measurement with high accuracy will be a seed for perspective view in a scienti c study. CRL should
scienti c study. Conversely, scienti c results will proceed with both types of development if possible.
stimulate more accurate system development. The
other one is a \spread promotion" loop. Being dif- 6. Closing Greeting
ferent from the previous one, this type of loop aims The closing greeting was delivered by Fujinobu
to reduce cost instead of increasing accuracy to dis- Takahashi, the vice-director of IERS TDC at Comtribute the system widely in the world. Miniatur- munications Research Laboratory.
ization of system can also be a goal. Even though

Photo. KSP SLR system under test observation at Kashima. During period of January
30-February 14 in 1997, Kashima and Koganei stations have made observation for major
geodetic satellites LAGEOS, AJISAI, STELLA and Starlette in order to check out ranging
precision and accuracy stability. Forty ve LAGEOS1&2 passes in total were analyzed to
produce baseline length between Kashima and Koganei with accuracy of 20-30 mm, although
the system were not fully equipped with those to meet nal speci cation. The four systems
have get together and will be con gured with a single telescope for colocation, a comparison
observation with each other at Kashima. (Hiroo Kunimori)

6

IERS TDC News No.10

Report of the Technical Work- A large part of the time was allocated for the stareports from many organizations to exchange
shop for APT and APSG in tus
the latest information among the APT and APSG
community. These reports ranged from the recent
1996 (TWAA96)

activities of global networks to status of individual observatories. The status report sessions were
Yukio Takahashi (takahashi@crl.go.jp),
then followed by technology development sessions
Yasuhiro Koyama and All sta s of Radioand science sessions. After these sessions, the open
Astronomy Applications Section of
discussion session concluded the workshop. On theCommunications Research Laboratory
last day (December 13, 1996), there were two excursion tours, one to Geographical Survey Institutein Tsukuba, and the other to the Tokyo HeadquarKashima Space Research Centerters of the Communications Research Laboratory
Communications Research Laboratory
in Koganei, Tokyo and to National Astronomical
893-1 Hirai, Kashima, Ibaraki 314, Japan
Observatory in Mitaka, Tokyo. We were gratefulTechnical Workshop for APT and APSG 1996 that many colleagues from 9 countries worldwide(TWAA96) was held at a hotel near the Kashima attended the workshop. We believe the scienti cSpace Research Center of the Communications Re- outputs and discussions during the workshop de search Laboratory from December 10 to December nitely strengthened our collaboration for the APT
13, 1996. The workshop was the rst joint techni- and APSG. The importance of observations using
cal workshop for Asia-Paci c Telescope (APT) and space geodetic technology in the Asia-Paci c area
Asia-Paci c Space Geodynamics (APSG) Project. are increasing, and there is much potential for colSince we considered there are many technical is- laboration in the APT and APSG. This workshop
sues commonly applicable to the APT and the was helpful in their co-operation and the exchange
Very Long Baseline Interferometry (VLBI) part of of the valuable information.
APSG, we decided to make the meeting a joint All sta s of the Radio Astronomy Applications
technical workshop for APT and APSG. While Section in the Kashima Space Research Center conAPT is a regional VLBI network established by tributed to various aspects to ensure the success of
the Asia-Paci c countries for Radio Astronomy and this meeting.
Geodesy, APSG was established to conduct Geodetic research of the Asia-Paci c region by utilizing 1. Participants
Space Geodetic technologies such as VLBI, Satellite Laser Ranging (SLR), and Global Positioning We listed 39 foreign participants.
System (GPS). Therefore, the workshop covered
Australia(7); D.Jauncey, J.Manning, J.Reynolds,
technical issues of VLBI, SLR and GPS, and sciM.Costa, P.Harbison, J.Lauf and P.Edwards.
ences of both Geodesy and Astronomy. The agenda
China(7);
Y.Shuhua, Z.Junliang, Q.Zhihan,of this workshop consisted of the following four
Z.Wenyao, C.Junyong, A.Yusup, and Z.Yang.
items.
Russia(7); M.Kaidanovski, A.Finkelstein, I.Ipatova,
I.Molotov, S.Likhachev, A.Rodin and E.Brumberg.
(1) Developments and New Technologies in VLBI,
USA(6);
J.Bosworth, T.Clark, A.Whitney, A.Niell,
SLR, and GPS.
V.Altunin and E.Himwich.
Compatibility issues of the VLBI data acIndia(4); A.Singal, S.Ananthakrishnan, H.Vats
quisition system were discussed.
and T.Das.
(2) Status Report.
Canada(3); W.Cannon, P.Newby and G.Feil.
Recent status of the APT and APSG
Korea(3); J.Hoon, M.Chol and K.Jongsoo.
projects, observation sites, and data proNetherlands(JIVE)(1); L.Gurvits.
cessing centers (including VLBI correlaGermany(1); Hayo Hase.
tor centers) were reported.
V.Migenes contributed only proceedings, al(3) Collaboration of APT and APSG.
though he could not attend this meeting.
(4) Other Projects.
For Japanese participants, 24 sta members of
Other projects such as VSOP and CRL attended this meeting. There were 34 parAntarctica VLBI experiments were dis- ticipants from other institutes, and 32 participantsfrom various companies. Total number of particicussed.
pants was 129.

May 1997

7

contribution to GIS (Geographic Information System). The committee on GIS has initiated an Asia
We summarize the presentations at this meeting. and Paci c Regional Geodetic Project for October
As the opening session, D.Jauncey in CSIRO pre- 1997. Third was to deliver information concerningsented the current status of APT and Ye Shuhua the new Field System which has been developed byin the Shanghai Observatory presented the recent NASA. Fifth was to adopt the proposals for APT
status of APSG projects. After the opening ses- experiments.
sion, the status reports of individual observatories and projects were presented with regard to 4. Proceedings
wide area networks and projects, regional networks
and projects, and the activities of individual in- We believe that this proceedings is a valuable
stitutes. Many important topics were presented: source for information in the APT and APSG com"CORE" and NASA Geodesy program, JIVE, munity, and also in the worldwide VLBI group.
GPS networks (WING), SLR network (WPLTN), Numerous copies of the TWAA96 proceedings are
Antarctica VLBI experiments, space VLBI projects available. For copies of the proceedings of this
(VSOP), LBA in Australia, KSP by CRL, the meeting, please contact Y. Takahashi (E-mail:Japanese VLBI network and VERA by NAO, VLBI takahashi@crl.go.jp).
in DSN, status report of GSI (GPS, SAR and
VLBI) and GMRT in India. Furthermore, it was Acknowledgments
very valuable to have status reports from Korea,
China, Australia and other countries. In this ses- We could hold this meeting as the host instision, there were 21 presentations.
with full support from Science and Technology
The third was a discussion about developments tute
Agency(STA) and Japan International Science andof technology. There were 26 presentations. We Technology
Center (JISTEC). Furtherdivided them into 6 parts as follows: (1) Antenna more, the staExchangeoftheadministrationin theand Receivers and Front-end, (2) Real Time VLBI, Kashima Space Research Center, andsection
thesta(3) Field system and scheduling, (4) Recorders and Standards and Measurements Division supportedof
Acquisition terminals, (5) Correlator, (6) Tropo- in holding this workshop. We are grateful tospheric Delay Correction. Each topic was discussed usthem for this support. Many participants visited
eagerly. Especially, the compatibility of scheduling, thismeeting from various countries. We are also
VLBI terminals and correlators were important for gratefulto all participants.
this meeting, together with the exchange of information for the new VLBI techniques.
The fourth session was concerned with Scienceand others topics. There were 7 presentations concerning VLBI and APT and geodesy and astronomy.
14 topics were presented by poster. The total
number of presentations at this meeting was 70.
For details we refer to the published proceedings ofthis meetings.
2. Presentations

3. Resolutions

There was an open discussion at the end of thismeeting. The conclusions and resolutions madein the open discussion session are summarized by
Dr. David L. Jauncey and Dr. John Reynolds. One
was to encourage the formation of the fundamental
reference and calibration stations in Asian-Paci cregion. The modern space techniques (VLBI, SLR,GPS etc.) together with other techniques are colocated and operated on a long term basis for theestablishment and maintenance of the global reference frame. Second was an expression of APT support for the acquisition of geodetic VLBI data as a

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IERS TDC News No.10

Recent Status of the Key mediately after the rst check-out observations at
on August 20, 1997, daily operation ofStone Project VLBI System Tateyama
the Tateyama station began on September 1, 1996.

It is a notable achievement that the new VLBI
station started regular observations without major
problems. This was possible because the construction and the preparation of the KSP VLBI stations
Kashima Space Research Center
were well organized and carefully designed. Since
Communications Research Laboratory
theTateyama station started participating in daily893-1 Hirai, Kashima, Ibaraki 314, Japan
KSP VLBI experiments, these experiments havebeen carried out with its full 4-station-6-baseline
con guration with on a daily basis. In this report,
the current status of the KSP VLBI system as of
1. Introduction
the time when 10th IERS TDC Meeting was held
In addition to the three VLBI stations for the on March 14, 1997 will be mainly described. In adKey Stone Project (KSP) at Kashima, Koganei dition, the improvements of the KSP VLBI system
and Miura, the fourth VLBI station at Tateyama since then, and the future plans for the project willon the tip of Boso Peninsula became ready for the also be reported in the last section.
VLBI observations in August, 1996 (Figure 1). ImYasuhiro Koyama (koyama@crl.go.jp)

36
109 kmKOGANEIKASHIMA

123 km
92 km
58 km

135 km

MIURA

35

35 km
TATEYAMA

139

140
Figure 1. Con guration of the Key Stone Project VLBI Network.

141

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May 1997

Table 1. Percentage of the successful experiments for each station

Month
September,1996
October,1996
November,1996
December,1996
January,1997
February,1997
March,1997

Kashima Koganei Miura Tateyama
96.7
96.7
83.3 93.3
93.5
96.8
96.8 93.5
80.0
93.3
93.3 83.3
90.3
96.8 100.0 100.0
96.8
90.3 100.0 100.0
100.0
100.0 100.0 100.0
100.0
100.0 100.0 66.7

experiment. This procedure is also performed automatically, and it tells system operator at Koganei
The daily observations of the KSP VLBI system station by e-mail if there is any problem. Whenare performed automatically. All four stations are the system operator receives an alarm message byequipped with two engineering workstations, one of e-mail, the cause of the problem is investigated andwhich is for the control of the observation system then resolved, if it is possible to do so from Koganei
and the other is for continuous data acquisition in- remotely. If an on-site repair is found to be necescluding the calibration data and the system moni- sary, related hardware vendors and CRL sta s are
toring data. These workstations are controlled and noti ed with detailed information. For example,
organized by the central control workstations lo- a PC at Tateyama station which controls the Ancated at Koganei central station and at Kashima tenna Control Unit failed to keep the internal clock,sub-central station. There are two central control although the PC clock is usually synchronized withworkstations to reduce the possibility of failure of UTC by using a GPS receiver signal. This probthe daily experiments. Since these two central con- lem caused data loss for the Tateyama station fortrol workstations are functioning identically and in- three consecutive experiments but the system wasdependently, the observations at remote sites are recovered within three days. On the other hand,still under control even if one of the two central this case can be considered as a demonstration ofcontrol system has a problem. The computer net- the robustness of the KSP VLBI Network in thework of the KSP Network is also highly reliable sense that an unpredictable failure at a remote site
since there is a redundant dial-up network line be- can be recovered within three days. In addition,
tween Miura and Tateyama and it acts as a backup the overall software system is being implemented soroute when one of the three network lines connect- that the same type of problem can be resolved froming four VLBI stations loses connection for any rea- central control system at Koganei or at Kashima.
son. Table 1 shows how the reliability of the KSP
VLBI system has been improved. The percentage 3. Quality of the Observed Dataof the successful experiments are counted for eachstation and tabulated in Table 1. In this table, an Starting on March 1, 1996, the VLBI observaexperiment is considered to be successful for one tions are performed with 16 channels each of which
station, if the site coordinates of the station can be have 2 MHz of video band width. Total speed of
estimated with sucient reliability. The redundant data recording is 64 Mbps, which is 1=4 of the maxcentral control system at Kashima started full op- imum recording speed of the KSP VLBI system. 10
eration in January 1997 and it improved the success channels are assigned for X-band and the other 6
percentage. Especially in February, it is noted that channels are assigned for S-band. Figure 2 and Figall experiments were successful during the month. ure 3 show the various aspects of the data quality of
Every morning, the observation tapes are re- the observed data for two baselines, one is between
placed by human operators at each station during Kashim11 and Koganei stations and the other is
one hour from 9:00 o'clock by Japanese Standard between Kashim11 and Miura stations. In eachTime (JST). After all the observation tapes are set gure, (a) the formal error of the baseline length
in the Digital Mass Storage (DMS24) system, all estimates expressed by the standard deviation, (b)tapes to be used in the next observation schedule root mean squared of the residual of the observed
are mounted into the DIR1000 data recorder and delay after the least square estimates, and (c) thethe quality of the tapes and whether the tapes are ratio of the number of delay observable which are
write-enabled are investigated, and in the end, all not used for the least square estimates to the total
the tapes are rewound and set in place for the next number of the data included in the Mk-3 database
2.Daily Operation

10

IERS TDC News No.10

10
0

5

(mm)

15

20

(a) Formal Error of Estimated Baseline Legth (Kashim11-Koganei)

95

96

97 (Year)0(psec)
100
200

300

(b) RMS Delay

95

96

97 (Year)

0

20

40

(%)
60

80

100

(c) (Bad Data) / (Total Number of Data)

95

96

97 (Year)

Figure 2. Three indices to evaluate the data quality of Kashim11-Koganei Baseline.

for each individual experiment session, are evalu- from the level of 60 psec to about 20 psec. This
ated and plotted.
was a result of the improved short time phase staThese gures indicates the data quality of the bility of the phase calibration signal at Kashima
data obtained in the daily KSP VLBI experiments. station. Before the improvements, the temperaThe most notable point is the evident improvement ture inside the receiver unit located below the 11m
in the formal error and RMS residual delay for both antenna dish was controlled in the range 25 6 1 C.
of the baselines from February 22, 1997. Before But it was found that this temperature control hadthat day, the formal errors of the baseline length been causing the short time periodic variation of
estimates were around 4 mm but improved to ap- the temperature inside the unit. The phase of theproximately 2 mm. The RMS delay was improved phase calibration signal is quite sensitive to the am-

11

May 1997

10
0

5

(mm)

15

20

(a) Formal Error of Estimated Baseline Legth (Kashim11-Miura)

96

97(Year)

97(Year)

97(Year)

0(psec)
100
200

300

(b) RMS Delay(c) (Bad Data) / (Total Number of Data)

0

20

(%)
60
40

80

100

96

96

Figure 3. Three indices to evaluate the data quality of Kashim11-Miura Baseline.

bient temperature and the phase variation causes perature controlled and the observations are pererror in the observed delay. If the variation is slow, formed in the time range from 00:00 to 05:30 lothe error of the time delay can be removed as the cal time when the temperature is most stable durclock di erence between two stations through the ing the day. An improvement of the temperature
VLBI data analysis. If the variation is faster than control system of the receiver unit with slow andthe interval of the clock parameter epochs which is smooth temperature control is considered and will
1 hour for the KSP data analysis, the delay error be implemented in the future. The phase calibracan not be removed and it degrades the estimated tion signal unit will also be improved with a small
results and increases the residual delay. At present, temperature control system inside the case of thethe receiver units of all four stations are not tem- unit to stabilize the phase of the signal.

12

IERS TDC News No.10

The other characteristic thing of concern in Fig- at 64 MHz prior to April 6, 1997. At present, miure 2 and 3 is the high percentage of invalid data nor problems and software developments for theto the total number of the available data for the automated processing are in progress. The 256
Miura station. This is shown in Figure 3 (c) only Mbps real-time VLBI experiments will be routinely
for the Kashim11-Miura baseline, but it is also true started near future.
for the other two baselines which include the Miura In the data analysis, a program dbupdate wasstation. This is caused by weak phase calibration revised to obtain the nutation o sets from thesignals recorded in speci c channels at Miura sta- IAU80 model provided in the IERS EOP Bulletinstion. The band-width synthesis software automat- and include the o sets in the Mk-3 database. These
ically rejects a data channel if the amplitude of o set values are now used in the data analysis.
the phase calibration signal recorded in the chan- Lastly, the phase calibration signal unit atnel is below 1% of the total power of the channel. Tatayema station was replaced on April 8, 1997.
At Miura station, the amplitude of the recorded Before it was replaced, the phase stability of thephase calibration signal is not uniform for all chan- unit was insucient. Now, the phase stability has
nels. When the system noise temperature is high been improved and the formal errors of the baseline
at low elevation angle or due to rainy conditions, lengths of the three baselines towards Tatayema
up to four observation channels are removed from are at same level as the other three baselines. The
the band-width synthesis software. In this case, power of the phase calibration signal at Miura stamuch data becomes invalid because of false detec- tion was increased and since then the ratio of intion of side-lobe of the delay resolution function. valid data to the total number of available data deThe cause of the weak phase calibration signal was creased. Although the Input Interface of the Miuradiagnosed to be a problem in the Input Interface station must still be repaired to make the phase(DFC2100) of the KSP data acquisition system. calibration signal level uniform among the 16 obAt present, solutions are being considered and the servation channels, the data quality of the Miura
station is now satisfactory.
problem will be solved in a near future.
4. Recent Improvements and Changes

5. Future Prospects

After the 10th IERS TDC Meeting was held on At present, the daily VLBI experiments of the
March 14, 1997, following new changes and im- KSP VLBI system are producing daily baseline
provements have been applied to the KSP VLBI lengths and horizontal station positions with formal errors close to 2 mm. Vertical station posisystem.
First of all, real-time VLBI test observations tions are estimated with formal errors of about 10
were performed for four consecutive days starting mm. The system development of the automatedApril 7, 1997. The observations were done using data processing system for the real-time VLBI obthe maximum data rate of 256 Mbps for 22 hours servations are in the nal stage, and the daily realfrom 10:30 local time each day. The tests were time VLBI experiments will start on a daily basis
nearly totally successful and the results obtained very soon.
from the real-time VLBI data were consistent withthe daily tape-based VLBI experiments performed

13

May 1997

The Multimedia Virtual Labo- quantities of data has not been able to be transby network.
ratory (MVL) and Its Applica- ported
Some of the MVL projects needing cooperation
tion to Cooperative Research between industries, academies, and administrative

organs, are carried out by TAO (Telecommunications Advancement Organization of Japan). And
Shin'ichi Hama (hama@crl.go.jp)
some, which should be led by the government, arecarried out by the CRL (Communications ResearchLaboratory, Japan). The latter ones are generally
Communications Research Laboratory
ambitious and science-oriented projects. We ex4-2-1 Nukui-kita, koganei, Tokyo 184, Japan
pect to establish the basic system in the rst twoor three years, and carry out experiments later.
The concept of an MVL (Multimedia Virtual With the construction of the MVL, researchers
Laboratory) was proposed by the Telecommuni- in di erent laboratories, institutes and universications Technology Council in May 1996, in con- ties can be connected for mutual cooperations tosideration of recent technological development in increase eciency and to reduce the costs of retelecommunications. The MPT (Ministry of Posts search and development. Particularly in VLBI andand Telecommunications, Japan) strongly recom- earth environment sensing, sharing a large quantity
mends the creation of the MVL, and began e orts of raw data between researchers is highly useful.
toward this end in 1997.
By connecting the radio telescopes and VLBI data
The MVL has many potential applications, such processors of the CRL's KSP (Key Stone Project),
as in teleconferencing, application sharing, wear- NAO (National Astronomical Observatory), ISAS
able computers, virtual reality using \cave," and so (Institute of Space and Astronautical Science), andon. But we would like to demonstrate the possibil- other institutes, as shown in the Figure, we exities for cooperative research in the VLBI eld, the pect to achieve such bene ts as distributed VLBIMVL is not merely \an improved TV phone." Re- data processing, comparison of correlation processsearchers in distant places have been able to com- ing between di erent systems, and realtime feedmunicate with each other for development of net- back of observation parameters.
work technology, as shown in Table 1. But large
Table 1. Communication between distant researchers

Communications
MediumConventional(telephone)
Network

Talk,
Atmosphere(TV)phone
TV conferencing
TV phone, VR3
TV conferencing
3 VR: Virtual reality

Type of information
Document, Figures,
Small data Photos
Fax
Fax
TV conferencing
E-mail,E-mail (MIME)
ftp, NFS WWW, X terminal

Control, Large data
Monitor (1 Gps)
modem{
(send MT)
ftp
?
rsh

14

IERS TDC News No.10

ÏâÞéæ÷æëäÞÓæïñòÞéÉÞßìïÞñìïö
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ëâñôìïè

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Âããâàñð
UEÐåÞïæëäìãÞéÞïäâîòÞëñæñöìãìßðâïóâááÞñÞ¥ßìñåðñìïâáÞëáãéìôæëä¦UEÏÞíæááâñâàñæìëìãðêÞééàïòðñÞéêìóâêâëñ
UEÃéâõæßéâìßðâïóÞñæìë¥áöëÞêæàãââáßÞàèìãíÞïÞêâñâïð¦UEÁæðñïæßòñâáíïìàâððæëäìãÓÉ¿ÆÞëáðöëñåâðæðìããÞæëñðìòïàâð
UEÀìêíÞïæðìëìãáæããâïâëñíïìàâððæëäêâñåìáð

Figure 1. Multimedia virtual laboratory.

15

May 1997

Overview of Development of for tape change is not necessary for 24 tapes. S2
terminal developed by Canada has used at
High-speed VLBI Terminal VLBI
128 Mbps. It has 4 or 8 or 16 channels. The VLBA
and the Compatibility of VLBI terminal developed by USA is 256 Mbps/4ch or
16ch is used in radio astronomy or geodetic VLBI.
Terminals
These three types of VLBI terminals are presently

available.
Recently, Mark-IV which will be used for 1 Gbps
(or /2Gbps ?) was developed in USA and the correlation center has been established in JIVE andKashima Space Research Center
other countries. Mark-IV is upward compatible
Communications Research Laboratory
with
VLBA. CRL has developed a new VLBI ter893-1 Hirai, Kashima, Ibaraki 314, Japan
minal which is used for 1 Gbps/1 channel (or 4channels?) mode to record on cassette tape. We
call this the "GBR system". These terminals are
I reported the compatibility of VLBI terminal in considered to be a next generation VLBI terminal.
TDC News No.9 in 1996, and would you like to I summarize the characteristics of VLBI terminalrefer it.
in Table 1. It is divided into two groups of recordThe international VLBI observations have been ing format. One group records the time signal in
conducted using Mark-IIIa VLBI terminal. The the observation signal. Another group records therecording rates of the system are 56 or 112 Mbps time signal on another track. The latter provides/14 channels, and 112 or 224 Mbps /28 channels. excellent time control.
The recording capacity is 1.1 Tb/tape. This is the Concerning the compatibility of VLBI terminals,
standard VLBI system.
the correlation center is important. I also summaK4 and KSP system developed by CRL in Japan rize the correlation centers in the world as shown
has been used for 64 Mbps, 128 Mbps and 256 in Table 2. I introduce the correlation center for
Mbps/16 channels. The recording capacity is multi-baselines. The most familiar correlation cenabout 0.8 Tb/tape. The VSOP terminal is similar ters are Haystack, Washington and Bonn for Markto K-4 system, but only 4 channels. Any operator IIIa VLBI terminals. Recently, the NRAO
Yukio Takahashi (takahashi@crl.go.jp)

Figure 1. The generation relationship of VLBI terminals.

16

IERS TDC News No.10

correlator was established for VLBA terminals, and IV correlation center. CRL has also developed theCanada and ATNF in CSIRO (Australia) are es- correlator for GBR which is the next generation
tablished for S2 terminals. The S2 correlation cen- VLBI terminal. It is for a single baseline, but obter in ATNF is important for APT (Asian Paci c servations of high sensitivity and wide bandwidth
Telescope).
will be possible for astronomy. If GBR can perform
In Japan, there are three correlation centers for correlation processing of 4 channels, then it is posmulti-baseline. First is the NAO FX correlator for sible to use the GBR system for geodesy. Table 5
VSOP. Second is KSP correlation center at CRL. It shows the performance of GBR system when used
is available for the real time VLBI experiments for for geodesy in two cases: 1 channels in the 22 GHz
the rst time in the world. Third is GSI correlator, band and 4 channels in the S and X bands.
which is similar to the KSP correlator.
Finally, we summarize the available VLBI termiI represent two correlations; one is the correla- nals of stations in Japan.
tion which mixes types of terminals, and another In December 1996, the technical workshop foris the correlation using next-generation VLBI ter- APT and APSG (TWAA96) was held at Kashima,minals. CRL succeeded in performing mixed cor- CRL in Japan. These topics were discussed at thisrelation between K4 VLBI terminal and Mark-III workshop and the di erent VLBI terminals were
[Takahashi et al., 1995]. CRL also developed the represented in the proceedings of the workshop.
rst copying system from the K-4 system to Mark- Please refer there for detailed information concernIIIa systems. Recently, the VSOP group at NAO ing VLBI terminal.
has developed a copying system between the different VLBI terminals of the VLBA, S2, VSOP- ReferenceK4 systems. Observations which mix the various
VLBI terminals cannot be available until the devel- Takahashi Y., et al. Data Processing Software andopment of this system. Table 3 shows the copying Data Analysis Software, J. Commun. Res. Lab.,42, pp31-42, 1995.
systems.
The correlation center of Mark-IV which is one of
the next generation VLBI terminals will be JIVE in
Europe. Bonn and others are planning for a MarkTable 1. Characteristic of VLBI terminals

channelMaximum recording speed
1. time signal in the observed signal
Mark-IIIa
14 ch/28 ch 56 Mbps/112 Mbps/224 Mbps
K4 standard
16 ch
64 Mbps(DFC1100 I/F)
VLBA
4 ch
256 Mbps
Mark-IV
16 ch1024 Mbps/2048 Mbps
2. time signal on the special track(No time signal in the observed signal)
S2
4 ch/8 ch/16 ch
128 Mbps
KSP (K4/256M version)
16 ch
256 Mbps(DFC2100)VSOP
4 ch
256 Mbps
GBR
1 ch(/4 ch)1024 Mbps

17

May 1997

Table 2. Correlation center for various VLBI terminals

VLBI terminal
USA, Europe
Mark-IIIa
Mark-IV
VLBA

Correlation Center
Mark-III correlator (XF type)
Haystack, Washington(USNO), Bonn
Mark-IV correlator (XF type) (BON, JIVE, WCO?)
JIVE, Bonn?, Washington(USNO)?
VLBA correlator (FX type)
NRAO
Canada, Australia, USSR
S2
S2 correlator (XF type)
Canada, Australia(CSIRO/ATNF)
Japan
K4 standard
K3 correlator (XF type) (CRL)
NAOCO (XF type) (NAO,GSI)
Mix of K4 and Mark-III K3 correlator (XF type) (CRL)
NAOCO (XF type) (NAO,GSI)
KSP (K4 256Mbps)
KSP correlator (XF type) (CRL, GSI)NAOCO (XF type) (NAO,GSI)
VSOP (K4 TCU)
NAO FX correlator (FX type) (NAO)
XF: FFT after cross correlation. FX: FFT before cross correlation.

Table 3. Copying (dubbing) system between the various VLBI terminals

Station
CRL
NAO
GSI

Dubbing typeK4 standard ! Mark-IIIa
S2$ VSOPVLBA$ VSOP
K4 standard ! Mark-IIIa (will be)
K4 KSP! VLBA, Mark-IV (will be)

Table 4. VLBI terminals at stations in Japan

K4 standard (64Mbps)+TCU
KSP (K4/256Mbps/16ch)
VSOP (256Mbps/4ch)
Mark-IIIa (54Mbps/14ch)
VLBA (256Mbps/4ch)
Mark-IV (1Gbps/16ch)
S2 (128Mbps/4 or 16ch)

Kashima KSP GSI USUDA Nobeyama Mizusawa Kagoshima
34m 26m 11m24 32m 64m
45m
10m
6m
4

4
4

4

4

18

IERS TDC News No.10

Table 5. Performance of GBR system for geodetic VLBI (Correlation amplitude: 0.07%, antenna slew
speed: 1deg/s, the mean angle between observations: 30deg, correlation synchronization: 10s, SNR at
X band > 30, SNR at S band > 25, ionospheric delay error < 20ps, the observation error: 50ps, IF:
100-1000MHz, experiment: 24 hours & one baseline, the duration of observation is enough to identify
the ambiguity.)

Mark-IV
GBR
GBR(1Gbps/16ch)(1Gbps/1ch)(1Gbps/4ch)
con guration of band
S:6ch, X:10ch
22GHz:1ch
S:1ch, X:3ch
32MHz/ch, 1bit 500MHz/ch, 1bit 64MHz/ch, 2bit
E ective Freq. Width
355MHz144MHz311MHzat X band
Side-lobe
0.58
{
0.58
ambiguity
50/100ns{
4ns
observation duration (sec)
8sec
7sec
12sec
number of observations
1730 obs
1800 obs
1660 obs
precision horizontal
1.1mm
1.0mm
1.1mm
vertical
3.2mm
3.1mm
3.2mm

May 1997

19

Plan for a High-rate Data (2) Video signal converter
multi-channel and wide video bandwidth
Recorder and a New Data Ac(32 MHz/ch * 32ch or 64 MHz/ch *quisition Terminal
16ch),(3) Input interface (or formatter)
Using high-speed A/D converters whichhave maximum sampling rate of morethan 150 Msps and 8-bit sampling in eachchannel.
Using digital ltering to minimize theCommunications Research Laboratory
phase atness,
4-2-1 Nukui-kita, koganei, Tokyo 184, Japan(4) Data recorder
Target maximum recording rate of 2048
Mbps, helical scan recording head (forAbstract
long-term continuous integration), cassette tape, low bit error rate (better thanAt the Communications Research Laboratory
10010), etc.
(CRL), we have been developing VLBI data acquisition terminals (K series) for mainly geodetic pur- (5) Output interface
Having modes comaptible with otherpose. The latest one is the K-4 system, which has
VLBI acquisition systems,
a maximum recording rate of 256 Mbps. The highend version of the K-4 system, which has fully auto- (6) Correlation processor
matic operation is utilized in the Key Stone Project64 MHz clock 32 channels, using ASIC
and formal error of a few millimeter over 100 km
technology for exibility, etc.
baselines is performed in daily observation, which
is published on the WWW (http://ksp.crl.go.jp). We welcome suggestions and comments about
Recently CRL has been developing a new VLBI this development project from a wide range ofrecording system using a GBR recorder for a near- VLBI users, especially concerning;
future system which is based on a data recorderthat has a maimum recording rate of 1 Gps, which (1) high rate data recorderinterface speci cations, recording timeis the state of the art. Besides the development ofper volume, bit error rate, etc.
the GBR system, CRL, as the IERS-VLBI Technical Development Center, is planning to construct (2) accurate instrumental delay calibration method
a next-generation VLBI system which will havefor bandwidth synthesis method,a maximum recording and data processing rateof 2048 Mbps in order to achieve highly sensitive (3) input interface
and accurate VLBI. This system will be applicanumber of sampling bits, speci cations of
ble to various elds of VLBI observation, such as
digital lter, sampling frequency, etc.
the micro-arcsecond-order radio astrometry to investigate the whole image of our Galaxy using the (4) compatibility with Mark-III, IV, VLBA, S-2,
K-4, etc.
apparent positional movement of quasars due to
We are planning that the output intergravitational lensing e ects [Hosokawa et al., 1997].
face will have an output mode for all or
several of the ones of the present VLBI
Concept of new system
acquisition systems.
The aim of this plan was not to develop a lowfor applications and science targets
price system but to develop a pioneering technology of Suggestions
the
new
VLBI
acquisition system are also resystem in order to comprehend the whole image of quested.
the Galaxy by detecting dark matter. A low-pricesystem will be developed in another plan.
We are starting the design of the new system for Reference
discussion as follows;
Hosokawa, M., K. Ohnishi, and T. Fukushima, Fluctuation of extra galactic reference frame due to gravi(1) Phase and delay calibration systemtational lensing in our Galaxy, to be published in the
Astronomical Journal, 1997.
TDB,
Hitoshi Kiuchi (kiuchi@crl.go.jp), Michito
Imae, Shin'ichi Hama, and Mizuhiko
Hosokawa

20

IERS TDC News No.10

Figure 1. Concept of new system

21

May 1997

Next Generation VLBI Terminals (Should be) Planned at
CRL

Multi-channel (>10) Type
(Geodetic Use)
- Extension of Conventinal System
High Performance
but Costly
Less-channel (< 4) Type
(Astronomy Use)K-4 System

Tetsuro Kondo (kondo@crl.go.jp)

Reasonable Performance
but Low Price, Small andCompact

Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314, Japan

High Speed Samplingwith Low Speed Recording

Figure 2. Next generation VLBI recorder system.

One is a multi-channel type mainly dedicated togeodetic rather than astronomical applications (seeGenerally speaking, a technical development is Kiuchi's report in this newsletter). Even thoughclosely connected with scienti c progress, and vice this system is still in the planning phase, almost
versa. We summarize this relation as follows.
all technical key items regarding this system are
Two feedback loops are considered between their already or will soon be realized. The other typerelations (Fig.1). One is an \accuracy improve- is one having fewer channels but wider bandwidthment" loop. In this feedback loop, the observa- per channel (Nakajima, 1996). The recording andtion system is designed to achieve the best mea- reproducing part of this system has been alreadysurement accuracy from the technical point of developed.
view. Cost-e ectiveness is sometimes regarded as In addition to persuing accuracy we should be
an unimportant factor in a system development. concerned about the distribution of terminals. If
High-accuracy measurements will stimulate scien- the price of VLBI terminal goes down with totalti c study, while scienti c result will stimulate performance being kept as accurate as current one,
more accurate system development.
terminals will be easily distributed widely. FurThe other one is a \spread promotion" loop. Be- thermore if it becomes compact in size, we will be
ing di erent from the previous one, this type of able to bring it easily anywhere in the world.
loop aims to reduce cost rather than to increase CRL should proceed with both types of developaccuracy, in order to permit wide dissemination of ment if possible.
the system in the VLBI community. Miniaturization of the system can also be a goal for porta- References
bility. Even though accuracy of measurements is Kiuchi, H., Plan for a high-rate data recorder and a newsacri ced, widely distributed VLBI terminals will data acquisition terminal, VLBI TDC News CRL,
produce new observational data which bring a new No.10 (this issue), pp.19-20,1997.
insights in science.
J., Current status of the gigabit VLBI
The former one, pursuing an accuracy improve- Nakajima,recorder system, VLBI TDC News CRL, No.9,
ment, can be divided into two types of terminal pp.17-18, 1996.
which are planned or almost developed at the Communications Research Laboratory (CRL) (Fig.2).

Achievement>Requirement

Technical Development(Accuracy Improvement)

Achievement~Requirement

Technical Development(Spread Promotion)
Low Price, Small Size
Requirement

Scientific Progress

Figure 1. Relation between technical development and scienti c progress.

22

IERS TDC News No.10

Preliminary Experiments of radio interferometer (optical-linked RF interferomwe can utilize absolute delay, and we do not
Radio Interferometer Using eter)
have to estimate the clock o set for baseline analFiberoptic Links Modulated in ysis because we use common local signals and every instrumental delay can be calibrated. AccordRadio Frequency
ing to Heki, [1990], the vertical component error of
the estimated position is larger than the horizontal component error because it is dicult to distinguish the parameter for the vertical componentof the station position from that for the clock o set in least-square parameter estimation. We canCommunications Research Laboratory
improve the vertical position error by introducing
4-2-1 Nukui-kita, koganei, Tokyo 184, Japanbaseline analysis, which does not need clock o set
estimation.
In conventional VLBI, it is impossible to usephase delay because an unknown phase introduced
1. Introduction
by an independent local oscillator is added to thephase. For the optical-linked RF interferIn Very Long Baseline Interferometer (VLBI), observed
ometer,however,
we use a common local oscillator
extremely stable frequency standards are required for frequency conversion
so that the phase di erfor each station. Data recorders are also needed ence observed by this interferometerbe treated
to record the signals detected at each observation as a phase di erence caused by groupcandelaythesite. Recently, real-time data transmission using case where no dispersion medium exists. Wein can
ATM switches has been initiated with VLBI by improve delay determination accuracy considerably
the Communications Research Laboratory [Kiuchi,
1996]. Data recorders are not needed in that sys- by introducing the phase delay.
tem, although frequency standards are still neces2. Con guration of the Systemsary.
It is possible to make a radio interferometer that Figure 1 shows the con guration of the opticalhas neither a data recorder nor frequency standards linked
RF interferometer. The signal of the radioat each observation site by introducing beroptic
links modulated in radio frequency. In this type of
Jun Amagai (amagai@crl.go.jp), Hiroo
Kunimori, and Hitoshi Kiuchi

Figure 1. System con guration of the optical linked RF interferometer.

23

May 1997

Figure 3. Relationship between the measured delay
obtained by the phase delay and the cable length
di erence. Although the measured delay is expected
to be 0, it decreases in proportion to the di erencein the cable length.

duced from the optical signal and injected into thereceiving system through a directional coupler installed just before the LNA. The calibration signal
returns to the analysis station via the same paththrough which the objective signal is transmitted.
3. Results of preliminary experiments

We investigated a radio interferometer withberoptic links modulated in radio frequency and
Figure 2. Equivalent input noise of optical link found that the practicable cable length was 65 km(factory data). A practicable cable length is ex- (Fig. 2).
pected to be 65 km in the case that allowable signal
We carried out preliminary experiments with ato noise ratio is 10 dB and optical ber loss for unit common signal instead of the signal coming fromcable length is 0.35 dB/km.
antennas and with optical ber cables whose length
was less than 10 m [Amagai et al., 1996]. The resultsof the preliminary experiments suggest thefrequency at 8 GHz detected by the antenna at each following
conclusions:observation site (objective signal) is ampli ed by a
low noise ampli er (LNA) and converted to an op- a) Short-term phase stability of optical signal
tical signal at the wavelength of 1.31 m. The optitransmission is sucient to maintain the corcal signals are transmitted through optical ber torelation amplitude.
the analysis station, where the electric signals are b) Long-term delay uctuation is less than 0.3
reproduced from the received optical signals. By
psec when the system is kept under the temusing a common local signal the reproduced signals
perature condition of 1 deg peak to peak.
are converted to video signals, which are processedby a correlation processor.
c) The optical ber delay is successfully compenDelay changes that occur in the optical ber are
sated for by a calibration signal in the radio
compensated for by the calibration signal, which
frequency which makes a round trip between
makes a round trip between the analysis station
the analysis station and the observation sites.
and the observation sites. A calibration signal genWe can determine the absolute delay not only
erated at the analysis station is converted to an opby group delay but also by phase delay. To use
tical signal at the wavelength of 1.55 m and is dithis cable delay compensation method, howvided into signals by an optical power divider. The
ever we must know the the precise ratio ofdivided optical calibration signals are transmitted
the refractive indices for 1.31 m and 1.55 mto the observation sites through the same optical(Fig. 3).
bers through which the objective signals pass. At
each observation site the calibration signal is repro- We plan to solve the refractive indices problem
by measuring the time necessary for a optical signal

24

IERS TDC News No.10

at a wavelength of 1.55 m to move back and forth References
between the analysis station and the observation
Amagai, J., H. Kunimori, and H. Kiuchi, Fundamental
site.
Experiments of Radio Interferometer using FiberopAcknowledgements

tic Links Modulated in Radio Frequency, Proceedings of the Technical Workshop for APT and APSG
1996, pp.269-273, 1996.

The authors would like to express their appreK.,Three Approaches to Improve the Estimation
ciation to Mr. Takeda and Mr. Kikuchi of Sum- Heki,
Accuracies of the Vertical VLBI Station Positions,J.
itomo Osaka Cement Co., Ltd for their help with Geod. Soc. Japan, Vol.36, pp.143-154, 1990.
the signal-to-noise analysis of the optical link. The Kiuchi, H., M. Imae, T. Kondo, M. Sekido, S. Hama,
authors are also grateful to Dr. Kondo of the Com- T. Yamamoto, H. Uose, and T. Hoshino, Real Time
munications Research Laboratory for his assistance VLBI of the KSP, Proceedings of the Technicalwith the correlation processing analysis.
Workshop for APT and APSG 1996, pp.125-129,
1996.

May 1997

E ects of Precession and Nutation on Short (a few Hours)
VLBI Experiments

25

1Z = (1 sin "0 cos H + 1" sin H)X+(1 sin "0 sinH 0 1" cos H)Y
1L = (X1X + Y 1Y + Z1Z)=L = 0
H = !t + H0
where ! is the angular velocity of the earth (1 cycle
Yukio Takahashi (takahashi@crl.go.jp)
is about 23 hours and 56 minutes) and t is a time.
H is the hour angle which changes diurnally.
Kashima Space Research Center
There are two types of e ects on the station poCommunications Research Laboratory
sitions (the wobble). One is an o set and another893-1 Hirai, Kashima, Ibaraki 314, Japanis a periodical term. Therefore, the station position changes with a period of 23 hours and 56
minutes. It is shifted by 4 minutes. When the obErrors in VLBI measurements are caused by servation time is shifted by about 4 minutes every
many reasons, such as noise, atmospheric scintil- day, the hour angle H is the same for every experlation, clock uctuation, the pseudo delay by the iment. Therefore, the e ects of the modi cation
calibration system, and inaccurate physical model. for the precession and nutation parameters on the
I investigated the e ects of the di erences of the positions are a bias. When the observation time isprecession and nutation parameters from the model xed, the mean station position during the experiment has an annual variation. Figure 2 shows theon the station positions.
The theoretical delay model of the Wahr's nu- image of the changes in the mean station positions
tation model (1980), and the Lieske's precession when experiments are conducted during 1 am tomodel (1976), which were adopted in IAU'80, was 6 am. The sine curve means the daily variation
used. The precession error is included in the es- of station position caused by the modi cations oftimated nutation parameters. Therefore, I show precession and nutation parameters (the abscissa
only the di erence of nutation parameters from the is time). The variation is shifted by 4 minutes perday. The mean position during 1 am to 6 am is
Wahr's model in Figure 1.
The di erences reach about 030 mas (mili arc- also changeable annually. If the schedule time issec) for nutation in ecliptic longitude, and 010 mas changed (for example from day to night), the estifor the ecliptic obliquity prior to the end of 1995. mated station position becomes discontinuous.
The amplitude of the modi cation for the nutation CRL has conducted the VLBI experiments ofmodel is a few mas for some periodical terms. The KSP (the Crustal Deformation Monitoring Systemmain reason for the di erences is due to modi - for Tokyo Metropolitan Area) since 1995. These
cation of the precession, which corresponds to the experiments are conducted during 5 hours everyday. The time of experiments is nearly xed. I inrate of ecliptic longitude of 03 mas/year.
These di erences a ect the station positions as vestigated the e ects of the di erences of the precession and nutation parameters from the model
shown in the following equations.
on the station positions. In the data of KSP ex~
1(PN)D(W B~ ) = D1(W B)
periments, the annual variations and the disconti0
1~~
nuity at the change of the observation time were1(W B) = D 1(PN)D(W B)
appeared [Takahashi et al., 1996]. These variawhere P, N are the rotation matrixes for preces- tions may be caused by the di erences of the nusion and nutation. D is the diurnal rotation ma- tation and precession parameters from the IAU80
trix, and W is the wobble. B~ is the baseline vector model. The typical baseline length is about 100
or station position vector. The e ect of the dif- km, and the di erences for the ecliptic longitude offerences of the precession and nutation parameters 040 mas and for the ecliptic obliquity of 010 mas
from the model on the wobble is similar to its ef- correspond to about 20 mm in components of thefect on station position. I represented the station station position. For an east-west baseline such as
positions 1X, 1Y , 1Z for the estimated nutation Kashima-Koganei, the amplitude of periodic variparameters 1 (ecliptic longitude) and 1" (eclip- ation is about 9 mm for Z component, while thetic obliquity).
e ects on X,Y components are like a bias. The
variation of Z components will be corresponding
1X = 01 cos "0Y
on north and vertical movements.
0(1 sin "0 cos H + 1"sin H)Z
1Y = 1 cos "0 X
Reference0(1 sin "0 sin H 0 1"cos H)ZTakahashi, Y., J. Nakajima, T. Iwata, H. Takaba, L.

26

IERS TDC News No.10

Figure 1. Di erences of adjusted nutation parameters (1 (dpsi) and 1" (deps)) from IAU80 model.

Figure 2. The image of the change in the mean station positions when experiments is conducted during
1 am to 6 am. The sine curve means the daily variation of station position caused by the modi cationsof the precession and nutation parameters. Abscissa is a time.
Furuya, Y. Koyama, and N. Kurihara, VLBI Error
and the Short Term Variation in VLBI, Proceedingof the Technical Workshop for APT and APSG 1996,
pp.225-230, 1996.

27

May 1997

GSI's New Correlation Processing System
Yoshihiro Fukuzaki(fukuzaki@gaos.gsi-mc.go.jp)
Geographical Survey InstituteKitasato-1, Tsukuba, Ibaraki 305, JapanThe Geographical Survey Institute (GSI) introduced a new correlator system. It has an ability to
calculate 3 station 3 baseline data at the same time.
Correlator unit is made by Cosmo Research Corp.
The software which controls the each unit is made Figure 2. A part of workstation (left) and correlaby Kety Corp. Ltd. These has been developed as tors in racks (right).
KSP correlator in Communication Research Laboratory (CRL). Bandwidth Synthesis software andsoftware making database developed by CRL areinstalled in the GSI correlation system. As a result, the GSI's system is almost same as the CRL's
one. In addition, we are using SOLVE which is
produced by NASA/GSFC as a baseline analysis
software. At present, we are analyzing observation data after 1993. The results will be used as
reference points of new Japanese Geodetic Datum
which will be published by 2000.
The GSI has a plan to re-construct the domestic
VLBI network and have 5 permanent VLBI sites.
The permanent sites will be used for regular observation. The new correlation system will analyze
the observation data which are recorded in the permanent sites.
Figure 3. Three auto-tape changers equipped with
K-4 recorders.

Figure 1. System control workstation and it's terminals.

Figure 4. Whole correlation system.

28

IERS TDC News No.10

VLBI Technical Development Center (TDC) at the Communications Research Laboratory (CRL)
is supposed to do1) the development of new observation techniques and new systems for advanced Earth's rotation observations by VLBI and other space techniques,2) the promotion of research in Earth rotation by advanced methods in VLBI,
3) the distribution of new VLBI technology.
The TDC meeting, attended by the ordinary members from inside the CRL and the special
members from the outside, is held twice a year. The special members advise the committee,
concerning the plan of technical developments. The TDC newsletter is published biannually by
CRL to inform the IERS community its current activities.
This news was edited by Tetsuro Kondo and Yasuhiro Koyama, Kashima Space Research Center,
who are editorial sta members of TDC at the Communications Research Laboratory, Japan. The
editors wish to thank Dr. O. J. Sovers for his kind help in the correction of the news translated
from Japanese to English. Inquires on this issue should be addressed to T. Kondo, Kashima
Space Research Center, Communications Research Laboratory, 893-1 Hirai, Kashima, Ibaraki
314, Japan, TEL : +81-299-84-7137, FAX : +81-299-84-7159, e-mail : kondo@crl.go.jp.
Summaries of VLBI and related activities at the Communications Research Laboratory
are available from the home page of the Radio Astronomy Applications Section of theKashima Space Research Center on the World Wide Web (WWW). The URL to view thehome page is : \http://www.crl.go.jp/ka/radioastro/" (Note! URL was changed from\http://apollo.crl.go.jp/").

TECHNICAL DEVELOPMENT CENTER NEWS No.10, May, 1997
International Earth Rotation Service - VLBI Technical Development Center News
published by
Communications Research Laboratory, 4-2-1 Nukui-kita, Koganei, Tokyo 184, Japan