TECHNICAL DEVELOPMENT CENTER NEWS No.12
International Earth Rotation Service - VLBI Technical Development Center News

published by

Communications Research Laboratory

COMMUNICATIONS RESEARCH LABORATORY

4-2-1 Nukui-kita, Koganei, Tokyo 184-8795, Japan

Serial No. 12
June 3, 1998

June 1998

CONTENTS
Overview of the Twelfth TDC Meeting : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 2
Technical Reports
Instructions to use K-4 VLBI system with FS9 software : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 6
K-4 VLBI data-acquisition system : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 8
Real-time VLBI system : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 12
Bandwidth synthesizing software KOMB : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 14
Data analysis software : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 15
The Kashima 34-m antenna status report : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 19
Preliminary experiments of improved optical-linked RF interferometer : : : : : : : : : : : : : 20
The comparison between VLBI and GPS data : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 24
News-News-News
Letter to the editor : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 27
Announcement
International workshop on geodetic measurements by the colocationof space techniques on earth (GEMSTONE) : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 5

1

2

IERS TDC News No.12

Overview of the Twelfth TDC 2. Activity Reports by Special Members
Meeting
Each special member reported on the current
Tetsuro Kondo (kondo@crl.go.jp)
Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-0012, Japanstatus of the activities of each organization.

National Research Institute for Science andDisaster Prevention (Seiichi Shimada)

Seiichi Shimada reported on the e ect of horizontal atmospheric asymmetry in GPS data analysis.
mentioned that the estimated horizontal staThe twelfth meeting of the Technical Develop- He
tion
position had been improved but this is is notment Center was held on March 10, 1998 at the the casefor the vertical position. He also demonKashima Space Research Center of the Communi- strated water
vapor distribution in a time-spacecations Research Laboratory.
domain obtained from GPS data analysis.

AttendanceHydrographic Department, Maritime Safety
Agency (Masayuki Fujita)

Masayuki Fujita reported on the current statusof SLR and GPS observations carried out by the
Kenichi Okamoto, Michito Imae, Mizuhiko Hoso- Hydrographic Department of the Maritime Safety
kawa, Yuko Hanado, Yukio Takahashi, Chi- Agency as follows.
hiro Miki, Hitoshi Kiuchi, Akihiro Kaneko, System improvement in accuracy targeting to 1
Taizoh Yoshino, Hiroo Kunimori, Jun Amagai, cm which is going on at the Shimosato SLR station
Hideyuki Nojiri, Toshimichi Otsubo, Masato Fu- has entered a nal phase.
ruya, Futaba Katsuo, Fujinobu Takahashi (KSRC: Measurements using a mobile SLR station madeKashima Space Research Center), Noriyuki Kuri- at Chichijima Island on the Philippine sea plate
hara (KSRC), Yasuhiro Koyama (KSRC), Junichi and which were separated by several years show
Nakajima (KSRC), Ryuichi Ichikawa (KSRC), motion of the island at 6 cm/year, which is conTadahiro Gotoh (KSRC), Tomonari Suzuyama sistent with VLBI measurements. Last summer(KSRC), and Tetsuro Kondo (KSRC)
the mobile station was located at Ishigakijima island. The measurements could barely be carriedout due to the system's age. Next scal year, theSpecial members
mobile SLR station will be located at Wakkanai on
Noriyuki Kawaguchi (National Astronomical Ob- Hokkaido.
servatory), Hideo Hanada (National Astronomical The Hydrographic Department is planning to esObservatory), Mikio Tobita (Geographical Survey tablish a fully automated GPS observation station
Institute), Masayuki Fujita (Hydrographic Depart- at Danjo islands located west of Kyushyu whichment, Maritime Safety Agency) Seiichi Shimada uses a solar battery and satellite communications(National Research Institute for Science and Dis- link.
aster Prevention), Kachishige Sato (Tokyo Gakugei Deployment of the D-GPS network by the Aids
University), and Masayuki Takemura (Kobori Re- to Navigation Department is going on as scheduled.
search Complex, Kajima Corporation)
About 30 sites will be established by the end of FY
The following special members could not at- 1998.
tend: Tetsuo Sasao (National Astronomical Observatory), and Shuhei Okubo (Earthquake Research Nobeyama Radio Observatory, National AsInstitute, University of Tokyo)
tronomical Observatory (Noriyuki Kawaguchi)
CRL members

Noriyuki Kawaguchi reported on the current status of the VERA project and VSOP as follows.
The main aim of the VERA (VLBI Exploration
1. Opening Greetingof Radio Astrometry) project has been slightly
Fujinobu Takahashi, the vice-director of IERS modi ed to emphasize the observation of invisiTDC at the Communications Research Laboratory ble objects, that is, the precise measurement of
the attractive motion of maser sources due to the(CRL), opened the meeting.
gravitational eld around black holes. An angle

Minutes3

June 1998

resolution (of better than) in an order of 10 mi- Geographical Survey Institute (Mikio Tobita)
cro arcsecs is required for this purpose. To obtain
this angle resolution at least four, and if possible Mikio Tobita reported that the Field System,
more than six, VLBI stations will be necessary for which is VLBI system control software developed
the VERA network in Japan. Urmuqi station will by the US VLBI group, has been successfully inbe a key station in improving the imaging ability stalled at the 26-m antenna site at Kashima. A
of the VERA network. Furthermore, VERA can fringe test using the Field System was successfully
have better continuum sensitivity than VLBA at carried out on March 3, 1998, and good fringes weremillimeter-wavelength by having wider observing detected.
He also reported that the construction of a 32bandwidth.
m
He also demonstrated the idea of a synthesis antenna at Tsukuba is complete. A fringe test
antenna by connecting a number of antennas dis- was done on March 20. This new antenna has atributed throughout Japan using ATM optical links high-speed slewing rate of up to 3 deg/sec. The
in a \writing with one stroke" manner. He demon- reference point of the antenna was designed not tostrated that this idea would allow observations at vary over 5 mm per year. This will be monitored
up to 8 Gbps, if the communication link has 10- through a local survey.
Gbps speed and ve stations are connected.
As for the VSOP, Kawaguchi reported that Mizusawa Astrogeodynamics Observatory,\HALCA" is in good condition and space VLBI ob- National Astronomical Observatory (Hideo
servations are carried out almost everyday. He told Hanada)
us that he hopes to compare VSOP results withhigh-angle resolution observation made by VERA Hideo Hanada brie y reported on the current
at a higher frequency in the future.
status of RISE (Research In SElenology) in the SEFinally, he requested the Technical Development LENE (SELenological and ENgineering Explorer)
Center (TDC) at CRL to maintain the 34-m an- project. According to his report, SELENE will entenna as long as possible because of its importance ter the PM phase in FY 1998. A workshop relating
to the Japanese VLBI community and to continue to RISE was held at Mizusawa in January, 1998.
the development of a reliable gigabit recorder. He
also hoped CRL would promote the development 3. Technical Development Reports
of a VLBI network in Japan connected by opticalber links like a KSP.
Tokyo Gakugei University (Kachishige Sato)

3.1 VLBI Technology Developed at CRL

Kachishige Sato introduced his recent work on VLBI technology developed at CRL was reviewd
the model calculation of rheological slip without by CRL members.
friction at the subducting plate boundary. This
study was motivated by the measurement of post- 3.1.1 Automated Observations System (Yaseismic crustal deformation measured by GPS after suhiro Koyama)
the 1994 Sanriku-Haruka-Oki earthquake, he said.
He evaluated two types of rheological model for CRL has been developing automated observalower crust and uppermost mantle, the \Maxwell tion/operation software for Japanese VLBI sincemodel" and the \three-element solid model", by the early 1980's. These are \KAOS", \MAOS",
comparing the actual observation results. He con- \NKAOS", and \KANAMEISHI" in chronologicalcluded that the \three-element solid model" better order. The latest one is for the Keystone Project.
The format of schedule les tends to be uni ed into
explains the observations.
the VEX format in the case of international VLBI.
Kobori Research Complex, Kajima Corpo- Therefore our VLBI operation software should bemodi ed to accept the VEX format. On the otherration (Masayuki Takemura)hand, the Field System, which was developed by
Masayuki Takemura reported on his recent work the
US VLBI group, makes it possible to control
investigating the historical seismograph records of hardware
by CRL, such as K4 and GBR
the 1923 Kanto earthquake. He pointed out that recorders. developed
Detailsarereported in this issue (seewhat happens after large earthquakes is important page 6).
in predicting future earthquakes. He said, we canlearn many things from historically large earth- 3.1.2 Antenna and Front-end System (Noriyuki
quakes.
Kurihara)

4

IERS TDC News No.12

CRL developed not only a receiver system for the and geodetic applications, wide-band VLBI anal26-m antenna at Kashima but also a GSI VLBI sys- ysis, di erential-VLBI analysis, and phase synthetem. CRL has been cooperating with the National sis analysis. One of the special members hoped
Institute of Polar Research on the Antarctic VLBI TDC/CRL would contribute to the data analysis
project. We can say that CRL has contributed to of the VERA project.
the progress of domestic VLBI stations. Thus CRL
has the potential of designing an antenna system 3.2 Current Status of the Keystone Project
up to 30-m and a high-quality and reliable S/X (Crustal Deformation Observation System
receiver system. CRL can also evaluate the total in the Tokyo Metropolitan Area)
performance of VLBI antenna.
3.1.3 Back-end and Recorder (Hitoshi Kiuchi) 3.2.1 VLBI System (Kouichi Sebata)

We developed a K-3 back-end and a recorder Kouichi Sebata reported on the current status ofsystem, which are compatible with the Mark-III KSP-VLBI as follows. Measurement accuracy has
system. Then we developed a K-4 back-end and been drastically improved since last autumn due
recorder which are more compact than the K-3 sys- to the change in observation tactics from a daily
tem's and easy to operate. After the K-4 VLBI sys- ve-hour session to a 24-hour session every othertem, a KSP recorder equipped with an automatic day. Even though KSP is designed for ease of use
tape changer was developed. This changer enables in operation, sometimes recovery is dicult fromus to make observations for a long time without an R&D experiments or unusual accidents. We areoperator. It also makes observation very easy.
compiling an operation manual as well as operation know-how in our computer to allow special
3.1.4 Real-time VLBI Technique (Hitoshi Ki- knowledge to be utilized and shared with operauchi)
tor. As the KSP operator can access these manuals through the WWW, he/she can cope with most
A real-time VLBI technique has been developed diculties without any specialist aid.
by CRL in collaboration with the Nippon Telegraph and Telephone Corporation (NTT). High- 3.2.2 SLR System (Hiroo Kunimori)speed optical ber links were constructed between
four KSP stations by NTT. We also developed Hiroo Kunimori reported on the current statusa real-time correlation processing technique using of the KSP SLR system as follows. The second obdata transmitted through high-speed links. Now
campaign of Kashima and Koganei stawe are conducting routine VLBI observations us- servation
tions
was
successfully carried out. Observations
ing 256-Mbps data.
were made at all four stations. KSP SLR started
regular observations on February 16, 1998.
3.1.5 Bandwidth Synthesizing Technique(Tetsuro Kondo)
3.3 R&D Experiment Reports

The history of bandwidth synthesizing software
in Japan was brie y reviewed. Initially it took
more than one hour to process only a single ob- 3.3.1 Survey Observation of Radio Sources
servation of about six minutes. Now this has be- using KSP (Akihiro Kaneko)come less than one minute due to improvements in Akihiro Kaneko reported on survey observation
software and computer hardware. One of the spe- using
the KSP VLBI facility. Last autumn, KSP
cial members of TDC requested the development changed
routine operation from an everyday baof real-time bandwidth synthesizing software.
sis to an every other day basis. Survey observations were then carried out during the rest period
3.1.6 Data Analysis (Yukio Takahashi)of routine KSP operation. The purpose of survey
Data analysis software dedicated to the geode- observation is to obtain information about the ansize of radio sources available for VLBI. So far
tic VLBI developed by CRL was reviewd. The gle
120
candidates in the Parks catalogue have been
software has been being updated year by year tosurveyed,
and fringes were successfully detected onre ect the latest physical model and theory into
57
sources.
analysis. The current software (for KSP) is third
generation in Japan. We plan to implement the following function in the future, such as astronomical 3.4 Others5June 1998

3.4.1 Current Status of Kashima 34-m Antenna (Eiji Kawai)

The current status of the Kashima 34-m antenna
was reported on by Eiji Kawai. As almost ten years
has passed since the antenna was constructed, deterioration can be seen in every part. As the antenna
is old, continuous upkeep is required to maintainit in good condition. One of the special membersof TDC appreciated CRL's e orts in assisting andcollaborating on VSOP. He requested CRL to keep
the 34-m antenna as long as possible. After Kawai's
talk a general question was raised concerning the
lifetime of the antenna. Replying to the question,
Mikio Tobita of GSI commented that it was 30
years in the case of a new GSI 32-m antenna.
3.4.2 Current Status of Next Generation
VLBI (Junichi Nakajima)

Junichi Nakajima reported on the current statusof the 43 GHz receiver currently under development. He also reported on the interference problem
at 1.6 GHz expected to arise from the low altitudecommunication satellites to be launched in the very
near future. The e ects and problems are now being investigated. One of the special members commented that this might cause severe interference
for the VLBI station in space.
3.4.3 Current Status of NAOCO at Kashima(Tomonari Suzuyama)

NAOCO, a simple correlator developed by the
National Astronomical Observatory, is temporarily being installed at Kashima to allow spectrum
observations to be made using the 34-m antenna.
Tomonari Suzuyama reported that the installationis going well.
4. Closing Address

The closing address was delivered by Kenichi
Okamato, the director of IERS TDC at the Communications Research Laboratory.

International workshop on
GEodetic Measurements
by the colocation of SpaceTechniques ON Earth(GEMSTONE)
25-28 January, 1999 Koganei, Japan
hosted by
Communications ResearchLaboratory

Communications Research Laboratory
will host an international workshop named
GEMSTONE (International workshop on
GEodetic Measurements by the colocationof Space Techniques ON Earth) which issponsored by the Science and Technology
Agency in Japan in January of 1999.
Importance of colocation between thespace techniques has been stressed. Although we had limited number of colocated stations in the past, the situation ischanging. We can study systematic errors
which may be invisible by a single technique, through the colocation. From a colocation, we may understand the behaviorof the atmosphere and other physical effects. These study will lead us the reference frame improvement. On the other
hand, we have to solve the technical problems such as ground surveying. This workshop will focus a topic of colocation in the
aspects of the technical points and its contribution to the geodesy and astrometry.
More information will appear on Web Site
\http://ksp.crl.go.jp/".

6

IERS TDC News No.12

the model 7624 is capable to generate 8 local frequency signals from 499.99 MHz through 999.99
MHz. The model 7631A video converter can convert 16 video channels and is used with the 7632A
local oscillator unit. The model 7623 video conYasuhiro Koyama1 (koyama@crl.go.jp) andverter can convert 8 video channels and is used
William E. Himwich2with the 7624 local oscillator unit. In this case, two
1 Kashima Space Research Center
sets of each unit are used to con gure 16 observaCommunications Research Laboratorytion channels for usual geodetic VLBI experiments.
893-1 Hirai, Kashima, Ibaraki 314-0012, Japan Both video converter units have multiple low pass
2 Code 926.9, NVI Inc.,
lters and the selectable bandwidths depend on theactual con guration of the unit.
Goddard Space Flight Center
Input interface unit digitizes the video band sigNational Aeronautics and Space Administration
Greenbelt, Maryland, 20771-0001 USA
nals and record these signals by controlling thedata recorder unit. DFC1100 has a single observation mode of 1 bit sampling - 16 channel - 4
1. Introduction
Mbps (64 Mbps total). All three models of the data
recorder unit can be used with the DFC1100 input
The K-4 VLBI data acquisition system has been interface unit. On the other hand, DFC2100 candeveloped by Communications Research Labora- be used with multiple observation modes. Among
tory and are currently used at several VLBI sta- of these modes, only three observation modes, i.e.
tions. The system can be used for various modes 1) 1bit-16ch.-4Mbps, 2) 1bit-16ch.-8Mbps, and 3)
of geodetic and astronomical VLBI observations. 1bit-16ch.-16Mbps, are currently supported by corRecently, NASA Field System software has been relators at Koganei (CRL) and Tsukuba (GSI) corimplemented to be able to control the K-4 system. relators, and are supported by FS9 software. The
In this document, characteristics and speci cations di erence of the three models of data recorder unitof the K-4 VLBI system are brie y described and is the maximum speed of the data recording. The
instructions to use Field System to control the K-4 maximum recording speed of model DIR1000 is 256
VLBI system are presented.
Mbps and all three observation modes are possible.
On the other hand, the maximum recording speedsof DIR1000L and DIR1000M are 128 Mbps and 64
2. K-4 VLBI System
Mbps, respectively.
The K-4 VLBI data acquisition system at an ob- Tape changer unit can change 24 ID1 casservation station consists of the units listed below. sette tapes for un-attended continuous observaIn addition to these units, there are output inter- tions. The current version of the FS9 software does
face units and correlator systems necessary at the not support the unit yet. The implementation istime of correlation processing, but these systems under progress.
are not supported by the Field System software
and will not be described here.
3. Setup Local Oscillator : : : 7632A, 7624
First, the /usr2/control/equip.ctl le shouldbeedited to re ect the actual con guration of the Video Converter : : : 7631A, 7623
data acquisition equipments. The type of rack Input Interface : : : DFC1100, DFC2100
should be set as either k41 if the combination of
7632A and 7631A is used, or k42 if the com Data Recorder : : : DIR1000, DIR1000L, model
binationof model 7624 and 7623 is used. The
DIR1000M
type of recorder should be set as either k41 if the
DFC1100 is used, or k42 if the DFC2100 is used.
 Tape Changer (Optional) : : : DMS24
Next, data and control cables should be conThe local oscillator unit generates phase locked nected. The input interface unit and the data
local frequency signals based on a reference 10MHz recorder unit is connected with one data cable(or 5MHz) signal. These signals are provided to the (VCD cable: blue) and one control cable (RS-422
video converter unit where the IF signal is down- cable: black). The data cable should be connected
converted to video band signals by using image to the DATA OUT connector of the input interface
rejection mixers and low-pass lters. The model unit and to the DATA INPUT connector of the data
7632A is capable to generate 16 local frequency sig- recorder unit. The control cable should be connals from 99.9 MHz through 519.99 MHz, whereas nected to the TO DR connector of the input interInstructions to use K-4 VLBI
system with FS9 software

June 1998

7

face unit and to the REMOTE 4 connector of the the control les are properly edited, run FS9 softdata recorder unit. All the K-4 VLBI equipments ware and issue a command rec=init from the FS9
are controlled via GP-IB data communication bus console terminal. If the con gurations were corfrom the FS9 host computer except for the data rect, the time code on the front panel of the input
recorder unit is actually controlled by the input in- interface unit turns to all-zero for about a second
terface unit via RS-422 but all the communications and then returns to the normal state. This comfrom the FS9 host related with the data recorder mand initialize the unit and is often required afare done with the input interface unit. Each unit ter the system con gurations were modi ed. Then
has a switch to set the GP-IB address. After set- execute tape command to check the data recorderting a unique address to each unit, all the units unit, vc and vclo commands to check the K41 typeshould be connected to the FS9 host computer by rack, and va vb vcla vclb commands to check
GP-IB cables. Total length of the GP-IB cable the K42 type rack. If the con gurations were corshould be kept as short as possible to prevent pos- rect, responses will be shown in the log window.
sible communication troubles (GP-IB speci cation If these commands did not work properly, beallows up to 20 meters in total). Then edit the sure to update the FS9 software to newer versions.
/usr2/control/ibad.ctl le and specify the con- The curreently available ocial version does not
gured GP-IB addresses. A sample le is shown support the K4 devices as of this time, and theactual version which is required to use the K4
below.
VLBI system will be announced in the near future. At the time of observations, a procedure
tc=dev02,4
le and a snap command le have to be preparedd4=dev04,4
v4=dev05,4
by using DRUDG software later than the version
l4=dev06,4
NRV980302.
ca=dev07,0
The K-4 VLBI system and other VLBI systems
can be connected to the FS9 host computer simulIn this example, the tape changer (tc) is set to the taneously. Which system is actually used can beaddress 2 and the input interface (d4) is set to the switched by editing the equip.ctl le. If one ofaddress 4, etc. If the k41 rack is selected (i.e. model the control les are modei ed, fs program must be
7632A local oscillator unit and model 7631A video restarted to make these changes e ective.
converter unit), 'v4' and 'l4' are used to specify
the GP-IB addresses of the video converter and the 5. Related Documents
local oscillator unit, respectively. If the k42 rack is
selected (i.e. model 7624 local oscillator unit and Following is a list of related documentations.
model 7623 video converter unit), 'va' and 'vb' you do not have these documents, please reare used to specify two GP-IB addresses of the two Ifquest
these documents to koyama@crl.go.jp or tovideo converter units, and, 'la' and 'lb' are used weh@vega.gsfc.nasa.gov.
to specify two GP-IB addresses of the two local
oscillator units.
 Journal of the Communications Research LabLastly, the le /usr2/control/dev.ctl should
oratory, vol. 38 (1991), 'special issue on the
be edited to re ect which GP-IB devices are used
results of VLBI experiments at the Communiat the FS9 host computer. Use 'board' for thecations Research Laboratory (1984-1990)'
GP-IB board device name if a NI GP-IB communication board is used, and use '/dev/ttyXX' if  IERS TDC News, issued biannually by Communications Research Laboratory
a GPIB-RS232C converter box is used where XX
depends on the actual con guration of the RS232C  Proceedings of the Technical Workshop for
port (S1 for com1 port for example).
APT and APSG, Kashima, December 1996
 VLBI Software Documentation, Field System,
4. Regular Operations
NASA/Goddard Space Flight Center, Space
Once all the equipments are connected and all
Geodesy Program8
K-4 VLBI
SystemIERS TDC News No.12

Data-Acquisition

Hitoshi Kiuchi (kiuchi@crl.go.jp)
Communications Research Laboratory
4-2-1 Nukui-kita, Koganei, Tokyo 184-8795,
Japan
Abstract: We have developed a new VLBI system

based on the conventional K-4 system. The system was designed to achieve automated operation Figure 1. Block diagrams of the new K-4 (observing
throughout the entire process, it is operated one station con guration).
operator for observation arrangement and correlation processing. The KSP system has two datatransfer systems, one is a tape-based system andthe other is a real-time system. The new acquisition system is designed to interface both systems,
the two systems are possible to be operated simultaneously. The new acquisition system has multibit quantization sampling modes. The total data
rate is up to 256 Mbps, and up to 16 video channels can be selected. Filterings are carried out inthe digital lter. The digital lter is used because
it results in good phase characteristics. This system is specially designed for the Key Stone Project,
and an input interface unit is incorporated in the
VSOP.
1. The New K-4 System

The KSP data-acquisition system (Figure 1), ahigh-end version of the K-4 system [Kiuchi et al.,1997], has a maximum recording rate of 256 Mbps
and is fully automatic. The di erent features of thesystems are given in Table 1. The data-acquisition
system consists of a reference distributor, IF dis- Figure 2. Block diagram of the new K-4 video contributor, local oscillator, video converter, input in- verter and local oscillator.
terface, output interface, data recorder, and digital mass storage system (automatic tape changer).
The local oscillator synthesizes the local frequency
signal for the video converter (Figure 2). This real-time VLBI system: in this issue) together withvideo converter converts windows in the IF-signal the time data. A block diagram of the input in(500-1000 MHz) input into video signals. The fre- terface unit is shown in Figure 3. The acquisition
quency conversion is done by a image rejection system has one-bit and two-bit sampling modes formixer using single-sideband conversion. The out- VLBI, and also has 4- and 8-bit sampling modes forput interface unit is used at a correlation processing general-purpose data acquisition. The anti-aliasing
ltering is done in analog (32 MHz), and after samstation for tape-based VLBI.
pling, the 16-MHz, 8-MHz, etc. ltering is done by
the digital lter. The advantages of using the dig1.1. Input Interface Unit
ital lter are that it can obtain good phase charThe input interface unit samples the video signal acteristics and can reduce coherence loss for widefrom the video converter (16-channel max.), and bandwidths. Suitable coecients of the digital lsends the digital data (256 Mbps max.) to the ter can be selected for each observation; for examdata recorder and/or the ATM transmitter (for a ple, the digital lter is used as a bandpass lter9June 1998

Table 1. The di erent features of K-4 systems and other VLBI systems.

Table 2. New K-4 data con guration * = Mark-III
mode, ** = VLBA mode, vs = VSOP mode.

Figure 3. Block diagram of the new K-4 input interface.

for the line observation. The coecients of the basically lowpass lter needed for Nyquist sampling
are provided in the read-only memory (ROM). The
output rate of data to the recorder or the ATM
transmitter can be selected from ve rates ranging from 16 to 256 Mbps. Time-code insertion
can be at uniformly bit-space or at uniformly timeinterval, or no time-code can be selected. In realtime VLBI, an uniformly bit spaced time code is 1.2. Data Recorderused, as required by the ATM side. The suitable
quantization threshold level of the A/D converter We adopted a rotary-head type recorder thatis adjustable. The con guration for one- and two- uses a cassette tape, which uses the ANSI (Ameribit sampling is shown in Table 2. This input in- can National Standards Institute) X3.175-1990 IDterface can be interfaced in analog to the Mark-III 1 format. The data recorder's error rates dursystem with no modi cations, using some BNC ca- ing recording and replaying can be read throughbles. This input interface is incorporated in the a host computer. Helical-scan recording is used to
VSOP (VLBI Space Observatory Program).
record high-rate digital signals. With a large cassette, the K-4 recorder provides up to 770 Gbits of

10
data-storage capacity. The recording time is 200
min. (large cassette, 16-mm thick tape), with a
64-Mbps recording rate. Recording and playback
are possible at di erent data rates: 256, 128, 64,
32, and 16 Mbps, making the data recorder suitable for many di erent applications. The playbackheads are placed so that the recorded data are
immediately played back during recording. This
read-after-write facility makes it possible to monitor the error conditions of recording in real time.
The bit010error rate after correction was better than
1 2 10 . The data recorder employs a built-in
diagnostic system, which is designed to detect operation errors or hardware faults. Error messages
or warning information is fed to the host computer
via the remote control interface, and to the front
panel display. The periodicity of the time code isundesired for spectrum analysis. Only the sampled
raw data are desired. The K-4 recorder has helical data tracks, two longitudinal annotation tracks
and a control track (Figure 4). The VLBI data arerecorded on the helical data tracks. A set of four
helical data tracks has one track set ID number,which is a sequential number as a tape counter.
The track set ID numbers are recorded on the control track, and can be read at any tape speed, evenwhen fast forwarding or rewinding. There is an
obvious relationship between the track set ID andthe time code, and it is possible to manage the timecode under the track set ID and time code block.
The time data are written over the data train as thetime code block in pre-observation. After the timecode block, the data timing is checked by track set
ID, which means that the output data are only raw
data digitized during observation. A data format
fully compatible with the conventional K-4 system
is also provided.

IERS TDC News No.12

Figure 4. Tape format and data format.

1.3. Digital Mass Storage System (Automatic Tape Changer)

In KSP, we adopted an automatic tape changer
as a digital mass-storage system (Figure 5). The
system accommodates one tape drive and 24 tapes,
or two tape drives and 16 tapes. The mass-storage
capability is up to 2.3 TB. A barcode reader is built
into the cassette-handling system to identify individual cassettes within the mass- storage system.
Information from the barcode reader is available
to the host controller via the remote control interface, and is written on the log which is utilized forcorrelation processing.
2.1. View of the data acquisition system

A photograph of the data acquisition system isshown Figure 6. From left side, an ATM transmit-

Figure 5. Digital Mass Storage System (Automatic
Tape Changer).

11

June 1998

Figure 6. View of the data-acquisition system.

Figure 7. View of the correlation processing system.

ter, an weather monitoring rack, an antenna control rack, a receiver control and monitoring rack, a lation processing systems, one is tape-based sysbackend rack, a digital mass-storage system. Three tem (front) and the other is real-time system (left
IF signals are received by IF receivers in the re- side). In the tape-based system, left side are digiceiver control and monitoring rack. The IF signals tal mass-storage systems, and right side are corresend to an IF distributor in the backend rack. The lation processor racks. In KSP, there are four sets
two sets of video converters (500 { 1000 MHz : 8 of digital mass-storage systems, and 6-baseline corch/unit) converts IF signal to video signal. And relators. The output interfaces are upper side, thethe other video converter (100 { 500 MHz : 16 correlators are lower two units in each correlation
ch/unit) is prepared as a conventional K-4. The processor rack, and other parts are blank panels.
video signals are send to the input interface (black It is possible to extend 10-baseline correlation syspanel), and the digital data is send to the digital tem with these three racks. The tapes are loaded
mass-storage system. The data is recorded on the to or unloaded from the data recorder (lower side)magnetic tapes, or by-passed to the ATM trans- automatically by digital mass-storage systems.
mitter.
2.2. View of the correlation processing room

A photograph in Figure 7 shows the view of thecorrelation processing room. We have two corre-

Reference

Kiuchi, H., J. Amagai, S. Hama, and M. Imae, K-4
VLBI data-acquisition system, Publ. Astron. Soc.
Japan, 49, 699{708, 1997.

12

IERS TDC News No.12

Real-time VLBI system
Hitoshi Kiuchi (kiuchi@crl.go.jp)
Communications Research Laboratory
4-2-1 Nukui-kita, Koganei, Tokyo 184-8795,
Japan
Abstract: We have developed a real-time VLBI sys-

tem that uses a high-speed ATM (asynchronoustransfer mode) network. In this real-time system,
observed 256-Mbps/station VLBI data is trans- Figure 1. Block diagram of the real-time VLBI sysmitted through a 2.488-Gbps ATM communica- tem.
tion network [STM-16] instead of being recorded
onto magnetic tape. The system was specially designed for the Key Stone Project (KSP), which is 1-byte is used as a sequence number to check forconcerned with measuring crustal deformation us- cell loss and mis-delivery. The signals input to theing four stations in the Tokyo metropolitan area ATM transmitter are written in the payload of thein Japan. Cross-correlation processing and data ATM cell in arrival order. The header of the cell,
observation are carried out simultaneously, and it which shows its destination, is attached when the
takes about two hours to analyze crustal defor- payload becomes full, and the cell is output to themation data after the VLBI observation is com- 2.488-Gbps transmission path [STM-16]. In thepleted. In regular geodetic VLBI experiments ev- KSP real-time VLBI system, the signals from theery other day lasting 24 hours, horizontal position four stations can be transmitted along one transuncertainty of about 1 mm and vertical position mission path, and a cross-connect switch connects
uncertainty of about 10 mm have been achieved.
multiple transmission paths. In the receiver,With the real-time VLBI system, one operator can thethemultiplexed
signal (cells) is separated into thehandle both the observation and the correlation data for each stationand cells are disassembled andprocessing. The system was designed to enable au- restored as digital signals
destination in
tomated operation throughout the entire process, the header data is checked.afterThethereal-timeand the obtained results are open to the public via system also has functions that compensate forVLBI
dethe Internet (http://ksp.crl.go.jp).
lay, absorb cell-delay uctuations in the transmission system, and compensate for mistaken cell de1. The real-time VLBI systemlivery and cell loss in the receiver. In real-time
the data from each station is data synchroWe have two VLBI systems in operation: one VLBI,
nized
inthe receiver (Figure 2). To absorb thetape-based and the other a real-time system. In transmission-paththe signal begins to accuthe KSP tape-based VLBI system, the observed mulate in the bu erdelay,
memoryfrom the time the time
data is recorded on magnetic tape at the observing stamp (every 64 Mbit) is received.
time code
site, and the tapes are sent to the correlation site is generated by the input-interfaceThis[
Kiuchi et al.,by mail. The analysis is done the next day, so it 1997]. The readout for the bu er memory starts
takes at least one day to obtain a measured value of immediately after the time stamps from all obsercrustal deformation. This delay was eliminated by vation stations have arrived allowing the timing tousing an ATM network [Sato et al., 1990]) to send be synchronized. Because the data is output to thethe VLBI data, which has a transmission capability correlator after the timing has been synchronized,of up to 2.488 Gbps through an optical ber link. the output data for each station is correct up to the
The four VLBI stations of the KSP are connected time on the time stamp. The KSP correlation proby this ATM network, and the data transmitted
is an XF type that uses eld programmablefrom these remote observing stations to the corre- cessor
gatearrays.
The maximum processing data rate islation site in Tokyo is processed in real time.
up
to
512
Mbps.
A block diagram of the real-time VLBI is shownin Figure 1. The ATM network transmits infor- 2. Results
mation in xed-length packets called cells. A cell
(AAL type 1) is composed of 53 bytes of data in The KSP system has two data transfer systotal, a 5-byte header and a 48-byte payload but tems: a tape-based system and a real-time sys-June 1998

13

Figure 2. Block diagram of the data synchro- Figure 3. View of the real-time correlation processnization and cross-correlation processing in the ing system.
real-time VLBI system. The data for an identical observation time taken at di erent stations
di ers in its arrival time due to the di erence of standard deviation, have been achieved. All rein the transmission-path length. To absorb the quired observation and data analysis processes aretransmission-path delay, the signal begins to ac- fully automated, and the obtained results are availcumulate in the bu er memory from the time the able via the Internet (http://ksp.crl.go.jp). CRL
time stamp is received. The accumulated period in has also developed an lower bits rate ATM system
the bu er memory is long when the transmission (STM-1: 155.6 Mbps) for international real-time
path is short, and vice versa. The readout from VLBI experiments. We carried out real-time VLBI
the bu er memory starts immediately after the time experiments between Koganei and Kashima using
stamps from all observation stations have arrived. the STM-1 ATM network, good fringes were obThus the timing can be synchronized.
tained.

3. View of the real-time correlation processing systemtem. The systems were designed to be fully automatic throughout the entire process, and only A photograph in Fig 3 shows the real-time correone operator is needed for observation and corre- lation processing system. Left side is ATM receiverlation arrangement. The two systems can be oper- and other two racks are correlation processor racks.
ated simultaneously. Using the tape-based system, The correlators are lower three units in each correwe carried out daily 5-hour experiments starting lation processor rack.
in January, 1995. The real-time VLBI system has
been used instead of the tape-based system sinceApril, 1997. After a continuous 120-hour 256-Mbps References
test session (from July 28 to August 1, 1997), a 24- Kiuchi, H., J. Amagai, S. Hama, and M. Imae, K-4
hour experiment was done every other day starting VLBI data-acquisition system, Publ. Astron. Soc.
on September 30, 1997. In these regular geode- Japan, 49, 699{708, 1997.
tic VLBI experiments, a horizontal position un- Sato, K., S. Ohta, I. Takizawa, Broad-band ATM
certainty of about 1 mm and a vertical position network architecture based on virtual paths, IEEE
uncertainty of about 10 mm, in terms of the in- Trans. Commun., 38, 1211{1222, 1990.
ternal estimation error represented by one sigma

14

IERS TDC News No.12

Bandwidth Synthesizing Software KOMB
Tetsuro Kondo(kondo@crl.go.jp)
Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-0012, Japan

A bandwidth synthesizing software can calculate
residual delays with a time resolution of more than
0.1 nsec from raw correlator output data by synthesizing multichannel correlation data. This software is called KOMB in the VLBI system developed by CRL. We describe in this report KOMB's
background and focus on its improvement in theprocessing speed.
Figure 1. An example of a ne delay resolution
In a geodetic VLBI observation, it is important function.
KOMB was named after its \comb" liketo measure the di erence between arrival times of structure which
is seen in the delay domain.
radio signals from a common source (quasar) at two
stations, which is simply referred to as the delay
time. Time resolution is approximately the orderof the reciprocal of the frequency bandwidth. Although we can record a limited amount of the frequency bandwidth signals on the magnetic tape,awide bandwidth is needed to accurately observe delay time. Bandwidth synthesizing was therefore
developed to increase the apparent bandwidth bycombining a number of narrow bandwidth data.
Phase calibration (PCAL) signals are injected in
the input of a low-noise ampli er in order to synthesize the di erent frequency channel data coherently. KOMB rst subtracts the instrumental Figure 2. Evolution of KOMB processing time forphase di erence of each channel from fringe phases one observation of six minutes.
by using PCAL phases. Then it calculates thene delay resolution function, which is de ned as afunction of the trial delay and the delay rates. We
will not include the detailed mathematical expla- was achieved by merely porting the software to annation of this data processing because it is not the HP1000/A900 minicomputer.
purpose of this short report, but we will show an In 1996, the software was ported to an
example of a ne delay resolution function calcu- HP9000/735 workstation and was modi ed to hanlated for actual VLBI data which was observed at 8 dle KSP's correlator output which is a 16-channel
GHz on the Keystone Project network (Figure 1). 32-bit-lag complex correlation data. By porting
KOMB was named after the shape of the ne delay KOMB into this powerful workstation, the processresolution function which looks like a \comb".
ing time signi cantly improved. It now takes less
KOMB was developed in 1983 on an HP1000/45F than 1 minute for a six-minute observation data.
minicomputer in order to process the K-3 correla- The improvement in processing time is summarized
tor output data which consists of 14-channel 8-bit- in Figure 2.
lag complex correlation data. Initially it took more A workstation version of KOMB is being used atthan one hour to process a single observation data the Geographical Survey Institute to process theirof six minutes. But by the end of 1984, the pro- domestic VLBI observation data.
cessing time improved to nine minutes for a sixminute observation. And 1989, it took only four
minutes. This drastic speed-up in processing time15

June 1998

data base setting software (KASET), correlation
processing software (KROSS), bandwidth synthesis
software (KOMB), tape format conversion software
Yukio Takahashi(takahashi@crl.go.jp)(KONV), a priori calculation software (KAPRI),
parameter estimation software (KLEAR) and data
Communications Research Laboratory
base handling software (KASTL). The software
4-2-1 Nukui-kita, Koganei, Tokyo 184-8795,
systems were developed using HP1000-45F and 10L
Japan
computer system. The characteristic of our system
is to be used the same data base (K-3 data base) by
all software from scheduling to analysis. The data
1. Introduction
base used the HP data base handler (IMAGE1000).
I introduce the VLBI software developed by CRL The k-3 software system was developed from 1981
(Communications Research Laboratory). As the to 1984 according to the following considerations;rst generation, CRL had developed our own soft- 1) that all software should be systematized toware system (K-3 software system) which is comuse the same data base and the same physipatible with the Mark-III system. It had been used
cal model;
for international and domestic VLBI during 1983- 2) its data base should be developed indepen1989. CRL developed a compact K-4 VLBI systemdently by CRL;
which uses the K-4 recorder, and also develop the 3) it should be compatible with the Mark-III sysdata processing software for the K-4 recorder andnew data analysis software. This system is a second 4) ittem;should introduce its own conceptual andgeneration which was used during 1989-1997. Since
physical model.
1993, CRL had developed the crustal deformation
monitoring system for Tokyo metropolitan Area. Data are combined for common attributes, andWe call it \Key Stone Project (KSP)". CRL devel- the key word (key item) of the attribute is added.
oped the new software. This is the third generation The data base is made up of the network of key
which is available since 1995. Figure 1 shows the items which are linked to detail values. The data
outline of VLBI data processing and analysis soft- for each item can be easily accepted at random byware. These software are referred to the Review selecting the key item. The K-3 data base is usefulof the Radio Research Laboratories Vol.30 in 1984 for random access, that is, the reading and modi (Japanese), some papers [Takahashi et al., 1991; cation of individual items. All software can use the
Takahashi et al., 1995] and the Review of CRL same values and data is transferred between software through the common data base. No inconsisvol.42 in 1996 (Japanese).
tencies exist for common values, such as physicalconstants, positions of sources and stations for all
2. K-3 software
software. However, the sequential access for the
The software system consists of 8 software pro- K-3 data base is slower than that for the Markgrams, namely; scheduling software (KASER), III data base. The K-3 data base requires a large
region of the disk and any change in the structure
would be laborious. The Mark-III data base is better in a minicomputer since access speed is a serious problem, but the conception of K-3 data baseis better in a high performance computer and forthe many modi cations of the data.
The data base setup software and data processing software must be developed by our own. A
priori software had the tide model with the 484
periodical terms [Manabe et al., 1984].
Data Analysis Software

3. K-4 software

Figure 1. Software developed by CRL.

CRL developed the \K-4" system using the K-4
recording system [Hama et al., 1991] and the analysis system for the new computer system HP1000
A900. For the precise compatibility, we adopted
the Mark-III data analysis software, such as thesoftware for the data base handler, the software

16

IERS TDC News No.12(CALC) for the calculated delay and delay rate,
and the parameter estimation software (SOLVE).
Thus, they are easy to install in the new computer
system and they are compatible with the worldwide
data base used in geodetic VLBI. However, we had
developed our own software to set up the data into
the Mark-III data base.
The new correlation processing software for K-4
system is controlled by the new computer system
HP9000-330. The BASIC language is used since it
can control the commands of GP-IB sequentially,
and it is especially easy to check and modify. The
correlation data send to other computer system
HP1000 A900, and the bandwidth synthesis software runs in the minicomputer.
A priori delay and rate are necessary to make acorrelation processing for every parameter period(PP). Their delay and delay rate are obtained using the 0th deviation ( ), the 1st deviation (_ ), the2nd deviation ( ), and the 3 order derivation ( )) Figure 2. The correlation processing among K4
with respect to time. In the old software, these recorders.
values are the coecients of Taylor expansion in
the middle of the observation. The di erence between the calculated delay and the true delay islarger at the beginning and end of each observation in according to be far from the middle of thecenter. In this software, the 0th, 1st, 2nd,3rd deviations are obtained using the approximation of
the four order polynomial formulation. The entire duration of each observation is divided into 4
parts (021T to 01T , 01T to 0, 0 to 1T , 1T
to 21T while 41T is the complete duration). Furthermore the delays are calculated for the 5 points(021T; 01T ; 0; 1T; 21T ). Calculated values foreach observation are calculated for the least square
ttings.
The calculation method in the correlation processing software are based on CALC. For atmospheric delay, we corrected for height in the zenith
path delay since some stations are located in elevated regions which are over 1000 m above sea
level.
This software can facilitate data processing both
3. The correlation processing between K4
among K-3 (Mark-III) recorders, and among the Figure
recorder and Mark-III recorder.
new K-4 recorders, and also the correlation between K-3 recorders and K-4 recorders. In correlation between the K-3 and K-4 recorders, the K-4
recorder serves as the master for synchronization 3 show the correlation processing for each system
and it is not controlled. This control of the syn- combination.
chronization is the same as the control among the The data base setup software inputs various data
conventional K-3 systems. One command \COR" for VLBI into the data base. We originally dein the recording system is used to automatically veloped this software. The bandwidth synthesis
synchronize K-4 system with other K-4 systems. software produces the les including the observaBefore ne automatic adjustment, rough tape syn- tion delay and delay rate for every observation andchronization to within 1 sec is achieved by using baseline. First, we collect the data from these
the position search command \PRL". Figure 2 and les to produce a new observation data le. Secondly, we calculated the ionospheric delay correc-

17June 1998

tions to input into the ionospheric correction data 5. Other software
le. Thirdly, we calculate the ephemeris data using
the JPL ephemeris \DE200/LE200" to input into We proposed the new estimation using the di erthe ephemeris data le. Fourthly, the temperature, ential method [Takahashi, 1992]. This method was
the atmospheric pressure, the humidity at the site applied to the clock estimation. It did not depend
and the cable delay calibration are retrieved from on judgments of analyst or need clock estimation.
the log le, and the interpolated data is calculated The estimation parameters in the geodetic VLBI
for each observation to input into the new calibra- are station positions, earth rotation parameters, attion data le. Fifthly, we prepare for the precise mospheric delay parameters, and the clock o set
earth rotation parameters, and we set up the earth and clock rate of a frequency standard. The clock
rotation parameters into the earth rotation param- epoch is divided into the estimation period. The eseter le. Finally, we collect the all data and we set timation parameter increases according to the clockparameters, the computer needs more time and aup them into the data base.
We also developed the software for converting large work area. The clock information is unnecthe recording data from K-4 tape to Mark-III tape essary for the geodetic VLBI, and it is undesirable
for both high and low density. It is necessary for to include it in the estimated parameters. We prothe case that we conducted the VLBI experiments pose an analytical method which uses the modi ed
using K-4 system and we must send the observation values without the clock information. This method
can be applied to other estimated parameters suchdata to NASA.
Furthermore, we developed the new parameter as atmospheric delay parameter.
estimation software (VLBEST). This estimation We assumed that the clock changes could be apmethod is the almost same as the estimation soft- proximated to the linear change during the threeware (SOLVE) except for the QR solution. We can observations. The modi ed delay value was calcumodify the estimated software easily, and it is used lated to cancel out the clock and clock rate using
three sets of data as following formula;for KSP software.
 0  +1
0 t +1 00 t +2(1)
4. KSP softwaret 0 t +1
+1
+2
Since 1993, CRL had developed the KSP where  is each observed delay, t is the observation
projects. In KSP, VLBI and SLR (Satellite Laser time, and i is observation number.
Ranging) facilities are established at four observa- We obtained the di erential values for each obtion sites in the Tokyo metropolitan area and the servations. The number of data is decreases by
precise position of four sites are measured every day only 2. However, the error matrix has the correlaor every other day [Takahashi et al., 1994; Kurihara tion between the observations. We must consider
et al., 1996]. The data of KSP is useful to research the e ects of the correlation between the neighborthe crustal deformation and the dynamics in this di erential values. The detail is referred to the paarea. The precision reaches less than 1mm and the per [Takahashi, 1992]. Our method is also suitablerepeatability is about 2mm for each experiment. for the use of frequency standard whose stability is
The real time VLBI system is necessary to moni- best for the 1000 seconds period.
tor the abnormal movement of the stations relatedwith the big earthquakes. The station movements 6. Conclusion and Future
are measured in mm precision just after the experCRL have been developed the VLBI software.
iment.
The observation is conducted by a remote con- The correlation mixing the di erent VLBI system
trol and the data analysis is carried automatically was realized at the rst time. The software was also
[Koyama et al., 1996a; Koyama et al., 1996b]. We corresponding to the new K-4 VLBI system. The
need the rapid results, and we realize the real software in KSP may the most advanced systemtime VLBI system in KSP [Kiuchi et al., 1996]. in the world. The many results was obtained by
New data correlation software had developed cor- our software, such as domestic VLBI, Antarctica
responding to real time VLBI [Kondo et al., 1996; VLBI, Japan-China VLBI, KSP etc.
The future plan of the software is to develop the
Sekido et al., 1996]. The system is completed andthe regular experiments have been conducted ev- di erential VLBI software for the new observation
ery two days automatically without no operator. by the high speed switching, which NAO in Japan
There is one operator at correlation center to check plans as VERA project. CRL has been developing
the system at the begin of the experiment and to the wideband VLBI system more than 1 Gbps. In
monitor the system only during working time. The the system, the number of channels is a few (one or
four channels). We will develop the data processing
software is very advanced.
i

i

i

i

i

i

i

i

i

i

18

IERS TDC News No.12

and analysis software for the system. Furthermore, Project),Proceeding of the Technical Workshop for
we want to develop the VLBI software available for ATP and APSG 1996.
both for astronomy and geodesy (astrometry).
Manabe, S., Y. Takahashi, H. Hanada, T. Ishikawa, M.
References
Hama, S., H. Kiuchi, III.3 K-3 and K-4 VLBI Data
Recorders, the special issue of the J. Commun. Res.
Lab. \Results of VLBI Experiments at the Communications Research Laboratory", 1991.
Kiuchi, H., M. Imae, T. Kondo, M. Sekido, S. Hama,
T. Yamamoto, H. Uose, T. Hoshino,Real-time VLBI
of the KSP, Proceeding of the Technical Workshop
for ATP and APSG 1996.
Kondo, T., H. Kiuchi, M. Sekido, KSP Correlator andData Reduction System, Proceeding of the Technical
Workshop for ATP and APSG 1996.
Koyama, Y., Automated Remote Operation Systemand Data Analysis System for the Key Stone Project
VLBI Network, Proceeding of the Technical Workshop for ATP and APSG 1996a.
Koyama, Y., Y. Takahashi, T. Gotou, K. Heki, Data
Analysis Software, The Review of CRL, Vol.42, No.1,
1996b in Japanese
Kurihara, N., K. Uchida, F. Takahashi, M. Imae,
T. Yoshino, S. Hama, Y. Takahashi, KSP Groupof CRL, The Crustal Deformation Monitoring System for the Tokyo Metropolitan Area (Key Stone

Fujishita, T. Sato, K. Koike and T. Yoshino, Physical Models Adopted in KAPRI, The Publication of
the International Latitude Observatory of Mizusawa,
Vol.XVIII, No2 pp 93-104, 1984.
Takahashi, F., M. Imae, T. Yoshino, Y. Takahashi, K.
Heki, C. Miki, T. Kondo, Y. Kunimori, N. Kurihara, T. Otsubo, H. Takaba, T. Iwata, H. Kiuchi,
Y. Koyama, Y. Hanado, M. Sekido, K. Imamura,
J. Nakajima, A. Sugiura, The plan of Metropolitan
Crustal Deformation Monitoring System by Communications Research Laboratory, Journal of Geodetic Society of Japan (CRCM'93 proceedings special
isuue), 1994.
Takahashi, Y., S. Hama, T. Kondo, III.5 K-3 softwaresystem for VLBI and new correlation processing software for K-4 recording system, the special issue of
the J. Commun. Res. Lab. \Results of VLBI Experiments at the Communications Research Laboratory", 1991.
Takahashi, Y., The Baseline Analysis by the Di erential Method in the Geodetic VLBI, Journal of theGeodetic Society of Japan, Vol.38, No.3, 1992.
Sekido, M., T. Kondo, H. Kiuchi, Y. Takahashi, Y.
Koyama, Correlation Process Control Software, The
Review of CRL, Vol.42, No.1 1996 in Japanese.

19

June 1998

The Kashima 34-m Antenna
Status Report
Eiji Kawai(kawa@crl.go.jp)
Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-0012, JapanThe Kashima 34-m parabolic antenna can receive 1.5, 2, 5, 8, and 22 GHz bands. Now weare equipping it with a 43 GHz band receiver. The
antenna was built in March 1988 and has recently
become too old to work properly. So we are currently taking steps to restore it. In order to pre- Figure 2. An AZ moter cover and a part of rail
vent corrosion of the antenna speci c direction due cover.
to geographical conditions, we regularly change thestow position of the antenna AZ (Azimuth) . As
the radio wave re ection paint on the subre ector
gets corroded, we are treating the damaged surface.
Maintenance is frequently done to prevent the topof the AZ rail from corroding. And to make it suitable for the Japanese environment. We installed an
AZ and EL (Elevation) motor cover to protect the
motor (Figure 1) and we also waterproofed the AZ
rail cover (Figure 2). Maintenance is dicult whena cover is used to protect the rail and wheel. So inorder to make maintenance easier, we made a rail
cover opening (Figure 3) and a transparent wheel
cover (Figure 4). Other minor but serious problems
are as follows. The receiver power was turned ooccasionally when the receiver control PC hang-up.
The azimuth encoder shows slight di erent value
from the real angle after the antenna turns 360 de- Figure 3. A part of rail cover and a rail cover opengrees in azimuth which in the future may obstruct ing.
high-frequency observations. These problems are
currently being checked on.

Figure 1. An AZ moter cover to protect the motor.

Figure 4. A transparent wheel cover.

20

IERS TDC News No.12

Preliminary Experiments of 2. Con guration of the System
Improved Optical-Linked RF
Figure 1 shows the con guration of the improved
optical-linked
RF interferometer. A signal with aInterferometerradio frequency up to 15 GHz (objective signal) is
detected by the antenna at each observation site
Jun Amagai (amagai@crl.go.jp),(Stations A and B), ampli ed by a low-noise amHiroo Kunimori, and Hitoshi Kiuchi
pli er (LNA), and converted to an optical signal on
the carrier at a wavelength of 1310 nm by a laser
Communications Research Laboratory
diode(#1 or #2). The optical signals are transmit4-2-1 Nukui-kita, Koganei, Tokyo 184-8795,
ted through optical bers to the analysis station,Japanand then electric signals are reproduced from thereceived optical signals (at #3 or #4). Common
local signals (SG) are used to convert the reproduced signals to video signals which are processed
1. Introduction
by a correlation processor.
We developed a radio interferometer with ber Delay changes that occur in the optical bers are
optic links modulated in radio frequency (Optical- compensated for by the calibration signals, which
linked RF interferometer) [Amagai, et al., 1996]. make a round trip between the analysis station and
We already showed the e ectiveness of this inter- the observation sites. We usually use comb tones
ferometer by some preliminary experiments but for the calibration signal [Rogers, 1970], but a noise
the delay compensation method had a problem. can also be used. The use of comb tones is assumed
After applying the delay compensation there still for the estimation of the practicable cable length
remained signi cant uncompensated delay caused (described in the next section). A calibration signal
by refractive index di erence. We improved de- at radio frequency (cal. signal) is generated at thelay compensation method using re ection of opti- analysis station, converted to an optical signal on
cal delay calibration signal. This paper presents the carrier at the wavelength of 1550 nm (#5), andthe con guration of improved system and the re- divided into two signals by an optical power divider
sults of signal-to-noise ratio analysis. The results (#6). Then each divided signal is transmitted usof preliminary experiments to con rm the e ective- ing a wavelength division multiplexer (WDMs #7
ness of new delay compensation method are also or #8) to each observation site through the same
presented.
Analysis Center#3

Station A
#1

LNA

E

O

O
#9
WDM

#17
E
O
Objective
SignalReflector

UnequalCplr#11(1.31mm)

#15
O E

#7
WDM

Cal.

H

E

#18

O

Reflector#10
WDM

UnequalCplr#12(1.31 mm)O

#8Cal. Signal

#16
O E

WDM

Cal.
(1.55mm)

E

#14
Cplr

Signal

O

E

SG
#5

#6

#2

Reflected
Cal.

#13
Cplr

(1.55mm)

Station B
LNA

Objective &Normal Cal.

E

Signal#4

O

E

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

Reflected
Cal.
Objective &Normal Cal

June 1998

21

optical ber that feeds the objective signal. At with controlling the distribution ratio of the uneach observation site the calibration signal is se- equal coupler installed at the antenna site. Table
lected out again by a WDM (#9 or #10) and then 1 lists the results of the estimation. The maximum
by using an optical coupler with unequal divide cable length is estimated to be 40.7 km. In thisratio (#11,#12) it is divided into two optical sig- condition, distribution ratio of the unequal coupler
nals with di erent intensity: normal cal. signal should be 0.927 : 0.073. Consequently, the practiand re ected cal. signal. The normal cal. signal cable cable length is estimated to be less than 40.7
is converted to an electric signal at the observation km.
site (#17 or #18) and is injected into the receiving system through a directional coupler installed 4. Preliminary Experiments
just before the LNA. The normal cal. signal is processed as the phase calibration signal of a usual The system con guration for the experiments
geodetic VLBI. The re ected cal. signal is directly is the same as that in Figure 1 except a comre ected by an optical re ector and returns to the mon signal, instead of a signal coming from ananalysis station through the same optical ber. At antenna, is fed into each receiving system. Cathe analysis station, the returned re ected cal. sig- bles with the same length and the same componal is selected out by the WDM (#7 or #8) and nents are used for each receiving system. In an
is fed to a photo detector (#15 or #16) via the actual radio-interferometer observation, objective
optical directional coupler (#13 or #14). The re- signals are noises from radio stars and are proected cal. signals converted to electric signals for cessed by a correlation processor to obtain the corboth stations are converted to lower frequency and relation function. From the correlation function weprocessed in the same manner as the normal cal. can estimate the time di erence between the arsignal.
rival times of the signals for two stations. But under the conditions of the preliminary experiments,
3. Practicable Cable Length
where the delay is too small and delay rate is comzero, too much undesired correlation prePracticable cable length is investigated from two pletely
vents
usfrom getting a good correlation function
points of view : the signal-to-noise ratio of the ob- and we cannot
estimate the time delay precisely.
jective signal; and the signal-to-noise ratios of the We therefore adopted
comb tones (with a frequency
calibration signals.
interval
of
10
MHz
and
frequency range fromThe equivalent input noise analysis of the opti- 8100 to 8500 MHz) for thea common
sigcal link with an Ortel 3541A laser diode and an nal. Because this common objectiveobjective
signalistheOrtel 4515A photo detector shows that the prac- same as the calibration signal and cannot be distinticable cable length to maintain coherence of the guished, we measured these two signals alternately.
objective signal was estimated to be less than 63.3 When these signals reached the analysis station,
km [Amagai, et al., 1996].
were converted to IF signals with a frequency
The conditions for the normal cal. signal and the theyrange
of 100 to 500 MHz and then converted again
re ected cal. signal are restricted by the input and to video
with a frequency range of 0 to 2
output powers. The power of one calibration signal MHz. Thesignals
local
frequency
for video conversion wastone at the input of the laser diode is 020 dBm; i.e., scanned from 109.99 to 489.99
with a 20-MHz
the calibration signal consists of the comb tones step. Each tone in the signals MHz
thus
appeared10
with a frequency interval of 10 MHz and a band- kHz in the video band. Phase was measuredat bywidth of 1 GHz, and maximum input power of the using a K4 input-interface [Kiuchi, et al., 1997],
laser diode is 0 dBm. The power of one normal cal. in which the signals were quantized for 1-bit andsignal tone at the injection point at the antenna site the phase of each tone signal was measured by synshould be 10 dB higher than the noise power level chronous detection using a 10-kHz signal generatedof 0148:6 dBm/kHz (the equivalent noise temperthe K4 input-interface.
ature of the low-noise ampli er is assumed to be insideWeevaluated the delay compensation method
100 K), and the power of one re ected cal. sig- mentioned
2. We determined the group
nal tone at the output of the photo detector at delay using intheSection
leastsquaresmethod applied to thethe analysis station should be 10 dB higher than spectra of phase di erences between
two receiving
the noise power level of 0142:6 dBm/kHz (thermal systems. The phase delay can be calculatedby dinoise of the photo detector is assumed to be 300 viding the phase di erence at the center frequency
K and equivalent noise temperature of the ampli- (8300 MHz) by the radio frequency. We prepareder following the photo detector is assumed to be
10-m cable, two 5-m cables, and one 3-m ca100 K). We estimated the maximum cable length of one
bleandmeasured the delays for four pairs of these
the optical ber according to the above conditions

22

IERS TDC News No.12

Table 1. Link budget for re ected calibration signal and normal calibration signal.
Re ected calibration signal
cal. signal power
O-E, E-O conversion
3-dB coupler
directional coupler
WDM
optical- ber cable
WDM
unequal coupler
re ector
unequal coupler
WDM
optical- ber cable
WDM
directional coupler

Loss [dB]
optical electric
-3.5
-3.5
-0.5
-12.2
-0.5
-0.8
-0.5
-0.8
-0.5
-12.2
-0.5
-3.5

-34.5
-7.0
-7.0
-1.0
-24.4
-1.0
-1.7
-1.0
-1.7
-1.0
-24.4
-1.0
-7.0

Power
[dBm]

-20.0
-54.5
-61.5
-68.5
-69.5
-93.9
-94.9
-96.6
-97.6
-99.2
-100.2-124.6-125.6-132.6

Normal calibration signal

Loss [dB]
optical electriccal. signal power
O-E, E-O conversion
3-dB coupler-3.5
directional coupler
-3.5
WDM
-0.5
optical- ber cable
-12.2
WDM
-0.5
unequal coupler-11.9
directional coupler (electric)
Conditions
cable loss (optical)
cable loss / km
cable length
distribution ratio

-34.5
-7.0
-7.0
-1.0
-24.4
-1.0
-23.7
-20.0

Power
[dBm]

-20.0
-54.5
-61.5
-68.5
-69.5
-93.9
-94.9
-118.6-138.6-12.2 dB
0.3 dB/km
40.7 km0.927 : 0.073

cables. Delays after the delay compensation are ex- can improve the precision of determining group depected to be 0 because the common objective signal lay and, consequently, the ambiguity problem menwas fed into both receiving systems.
tioned above can be resolved.
Table 2 lists the measured group delay and the Figure 2 shows the observed phase delays obphase delay for four pairs of cables. The errors tained with delay compensation using a re ected
listed in the table were calculated from the phase cal. signal and those obtained with not using a
residuals after least square tting. The determina- re ected cal. signal. For the latter case, we usedtion precision of the phase delay is more than 100 nominal refractive indexes of 1.44692 for the wavetimes better than that of the group delay. The re- length of 1310 nm and 1.44402 for that of 1550
sults show that every observed delay was less than nm to compensate the e ect caused by the di er100 psec and the cable delays were almost com- ence of refractive indexes. The gure shows that
pensated for successfully, however for group delays an expected phase delay of zero was observed when
there still remains signi cant uncompensated de- using a re ected cal. signal for each cable length
lay for the cases of the cable length di erences of di erence except 2 m. We can also see that the7, 5 and 2 m. The ambiguity of the phase delay absolute value of the phase delay obtained withis a half of the radio frequency; i.e., 60.2 psec in out a re ected cal. signal increases proportionally
this case. The observed group delay should thus to the cable length di erence. The reason for thisbe within +=0 30 .1 psec to get the correct phase proportional increase is thought to be due to the indelay. Though we could not get the correct phase correctness of the refractive indexes. From this exdelay, except for the cable length di erence of zero, periment, we con rmed that by using the re ected
the phases for every frequency component after de- cal. signal we can measure absolute delay within
lay compensation were less than 10 deg and were an error of 100 psec for group delay and 1 psec for
not consistent with the observed group delay. The phase delay.
observed group delays were therefore apparent andthe cable delay compensation was thought to be 5. Conclusion
properly applied. The phase delays listed in Table 2 were calculated by using expected ambigu- We investigated a radio interferometer with
ity instead of observed group delay. Though to- ber-optic links modulated in the radio-frequency
tal band width was limited to 400 MHz by the in- range. By analyzing the signal-to-noise ratio, it
strument available for this experiment, a system was found that the practicable cable length is limwith the bandwidth of 1 GHz is now available. Us- ited to 40.7 km by the link condition for the caliing the system with such a wide bandwidth, we bration signal.

23

June 1998

Table 2. Delay measurements.

cable length di erence [m]7520Delay [psec]
group delayphase delay-54.0 6 31.9
-94.6 6 38.1
-33.1 6 32.4
7.4 6 21.5

-0.33 6 0.44
0.39 6 0.53
-0.95 6 0.45
0.10 6 0.30

that we can determine the absolute delay not only
for group delay but also for phase delay, we shouldnote that it is dicult to use phase delay for an
actual experiment where an objective signal passes
through a dispersive medium because the phase delay does not directly correspond to the group delay
in such a condition.
In future research, we will conduct an experiment with a real radio-interferometer system todemonstrate the e ectiveness of the optical-linked
RF interferometer.
References
Amagai, J., H. Kunimori, and H. Kiuchi, Fundamental
Experiments of Radio Interferometer using FiberopFigure 2. Relationship between the measured phasetic Links Modulated in Radio Frequency, Proceeddelay and the cable length di erence.
ings of the Technical Workshop for APT and APSG
1996, pp.269-273, 1996
Rogers, A. E. E., Very Long Baseline InterferomeThe results of preliminary experiments with this try with e ective band width for phase- delay meaRadio Science, vol.5, no.10, pp.1239-1247,
interferometer lead to the conclusion that the surement,
Oct.
1970.
optical- ber delay is successfully compensated for(within an error of 100 psec for group delay and 1 Kiuchi, H, et al., K-4 VLBI Data-Acquisition system,
psec for phase delay) by calibration signals in the Publ. of Astron. Soc. of Japan, vol.49, no.6, 1997.

radio-frequency range. Though we demonstrated

24

IERS TDC News No.12

The Comparison between VLBI Japan constructed by GSI. The data of GSI and
KSP data were opened by WWW. The GPS staand GPS datation near Miura is not good, and we use the GPS
Yukio Takahashi1 (takahashi@crl.go.jp),
Yasuhiro Koyama2 , Ryuichi Ichikawa2,
Hitoshi Kiuchi1 , Akihiro Kaneko1,
Taizo Yoshino1, Masato Furuya1 ,Koichi Sebata1 , Tetsuro Kondo2 ,Noriyuki Kurihara2, Mamoru Sekido2 ,Junichi Nakajima2 , Eiji Kawai2 ,Fujinobu Takahashi2 ,and Kenichi Okamoto1
1 Communications Research Laboratory
4-2-1 Nukui-kita, Koganei, Tokyo 184-8795,
Japan
2 Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-0012, Japan

data of Yokosuka station a little far from Miura.
Other GPS stations are located a few km within
the VLBI stations. We can compare the VLBI data
and GPS data.
At rst, we compare the data quality of VLBI
with GPS in this network. The quality and reliability of VLBI and GPS data are obtained in thedomestic network. Secondly, we indicate the variations with the periodic terms of one month to one
year for both VLBI and GPS data. We are interested in the true and pseudo variation of the station
position.
2. Comparison of VLBI and GPS data
2.1 Velocities

The velocities of Koganei, Miura, Tateyama stations relative to Kashima stations are compared.
measurement error of velocities in KSP are
VLBI and SLR revealed the current plate motion The
0.2mm-0.5mm/year
for horizontal movements, andwithin a precision less than 1mm/year. Recently, 1-2mm/year for verticalmovements. The measureGPS are observed the detail crustal deformation in ment errors of GPS stations
are similar to VLBI
dense. It is important to compare the data reli- data. The velocities of GPS stations
are di erent
ability between these measurements (VLBI, SLR, from the velocities of VLBI stations. The
discrepGPS)
ancyis
0.7mm/yearforthehorizontal
movements
CRL (Communications Research Laboratory) Koganei station and 2mm/year for other stahad established the domestic network of the oftions.
It is 3 times of the measurements error. The
Crustal Deformation Monitoring System in the discrepancy
of vertical movements is greater thanTokyo Metropolitan Area. We call this projects 8mm/year. The
movements is not uncer\Key Stone Project (KSP)". The KSP is useful to tain for the shortvertical
period.
compare the results among VLBI, SLR and GPS.
The four stations are Koganei in Tokyo, Kashima
in Ibaraki, Miura in Kanagawa and Tateyama in 2.2 Data quality and reliability
Chiba. The baseline lengths are from 30km to We investigate the data quality and reliability
110km. The VLBI antenna is 11m antenna and of VLBI data in KSP and GPS data. Since 31th
SLR is 75cm optical telescope.
1995, the 5 hours VLBI experiment in the
Almost daily 5 hours VLBI observation was January
modeof
was started in KSP. There arestarted since 31th January in 1995 in the mode of two epochs56Mbps
whenthestatus of data were drastically
56Mbps on the baseline of Kashima and Koganei. changed. The rst epoch
was on 19th February in
The Miura and Tateyama stations were partici- 1997 (epoch 1) when the observation
mode changes
pated in the VLBI experiments on December 1995 to 256 Mbps (still 5 hours observation),and theand on September 1996, respectively. The daily 5 second epoch is 30th September 1997 (epoch
hours VLBI observation in the mode of 256Mbps when the 24 hours experiment in the mode 2)of
was started on 19th February 1997. The 24 hours 256Mbps was started. The PCAL at Kashima staVLBI experiments were started on 30th September tion was improved near epoch 1, and the quality
1997 every other day. The real time VLBI system the data related with Kashima station was imhas been available in our project (KSP) in coop- ofproved.
eration with NTT company in Japan since April We investigate the r.m.s. of the averaged values
1997. The correlation is done in real time. The within any interval which the data period is divided
SLR observations were started in 1997. There are into. Figure 1,2 shows the r.m.s. of the averaged
GPS stations of GSI near KSP stations within a values for the east and upward movements at the
few km as stations of the dense GPS network in
1. Intoroduction

25

June 1998

Koganei station relative to the Kashima station.
(a) means the data of 5 hours 56Mbps/64Mbps
VLBI experiments till epoch 1. (b) means thedata of 5hours 256Mbps VLBI experiments during epoch 1 to epoch 2, and (c) means the data of
24hours 256Mbps VLBI experiments since epoch 2.
The dispersions of GPS data since August 1996 arealso indicated in the Figures as the data (d).
The values of 1 day (faster variations) means theerror of each data. The errors of horizontal move-

Figure 3. Comparison between VLBI and GPS ofpattern of horizontal movements of Koganei relative to Kashima from 1997.10.1 (30days shifted average).

ments are 4-6mm, 4mm, 2mm and 2mm for 5hours
64Mbps VLBI, 5hours 256Mbps VLBI, 24 hours
256Mbps VLBI and GPS in this turn. Each data
error of GPS is similar to one of 24hours VLBI
data. Each data error of the vertical movement is
2-3cm, 2cm, 1cm and 1cm in this turn, respectively.
The physical interpretation is mainly revealed by
Figure 1. Comparison of r.m.s of the averaged the systematic variation. However, each errors has
East-West movements between VLBI and GPS a large random variation, and it is dicult to redata (Kashima-Koganei 109 km).
veal the physical phenomena. If we average eachdata, large random errors are canceled out and thesystematic variation appears. Furthermore, we areinterested in the variations with the periodic terms
from one month to one year, that is, seasonal andannual variation. It is important to know how theposition changes beside the velocity. We examine
the errors (reliability) of the variations with theterms longer than one month. For these variations,the horizontal errors are 1mm, 0.5-1mm and 0.5mm
for GPS data, 5hours 256Mbps data and 24hours
256Mbps data in this turn, respectively. The vertical errors are 5mm, 5mm and 2-4mm in this turn,respectively. In general, the reliability of the variations longer than one month by VLBI is better
than GPS data. The VLBI data may be stable forthe long period than GPS data.
2.3 Pattern of the movements
Figure 2. Comparison of r.m.s of the averaged
Upward movements between VLBI and GPS data
(Miura-Tateyama 35 km).

We investigate the horizontal movements. We
plot the trace of the horizontal movements. Eachdata has a large random error, and we use an averaged value within a interval. The averaged interval
is 30 days, and we use the box average (shifted average). The systematic variations longer than 30

26

IERS TDC News No.12

tematic variations of VLBI data is di erent fromGPS data. However, the ne variations shorter
than one week are sometime similar between VLBI
and GPS data. These ne variations may be causedby atmospheric e ects.
We also investigate the variation of whole GPS
raw data relative to time. The GPS data at somestations is seemed to be in annual GPS has a little
large systematic variation for long term at somestation. One reason of the systematic variationin GPS data may be the change of the lengthand trend of GPS pole caused by the temperaturechange.
3. Conclusion

We conclude the comparison between GPS andVLBI data as follows;
1. KSP is the good test-bed to make a comparison among VLBI, SLR and GPS.
days are found. We also compare the pattern of 2. 256Mbps 24 hours experiments at KSP is thethe horizontal movements to check the reliability
same quality as GPS data for each data.
of the systematic variations. If the variations are 3. VLBI is better than GPS for short term varisimilar between the di erent measurements techation longer than one month.
niques, such as VLBI, GPS and SLR, the variations 4. The pattern of horizontal movements of KSP
is true. Figure 3 shows the patterns of horizontal
VLBI data is disagreed with one of GPS data.
movements for 24hours 256Mbps VLBI data and 5. The
variation within one week is agreed withGPS data during October to December in 1997.
GPS.
It may be caused by the atmosphericThis is the movements of Koganei station relativeeects.
to Kashima station. The right gure is VLBI data,
and the left is GPS. The scale is the same. The pattern of the horizontal movements for VLBI data is Acknowledgments
di erent from one for GPS data. Figure 4 shows
the box averaged values within 30 days for the east The GPS data is produced by GSI (Geographic
and north movements of VLBI and GPS data on Survey Institute) in Japan. We are grateful for GSI
Koganei-Kashima baseline since 1997. The varia- sta s.
tions vs. time are found in detail. The large sysFigure 4. VLBI and GPS variation on KashimaKoganei 109 km.

27June 1998-News-News-News-News-News-News-News-News-News-News-News-News-

Letter to the Editor

Dr. Harald Schuh of DGFI (German Geodetic Research Institute) sent a following letter to the editorof TDC News. We are pleased to get his acceptance to give it as an article of the TDC News.

Dear Dr. Kondo,

Munich, May, 6th, 1998

Last week an important national conference on Earth rotation and reference Systems took placein Wettzell. One of the most exciting topics was the real-time VLBI. In my talk, I referedto the Japanese Key Stone project as the world-wide rst successful realiziation of broad-band
VLBI in real-time. Real-time VLBI was also a main topic in a symposium on 'Instrumental
challenges in geodesy' at the XXXIIIrd General Assembly of the European Geophysical Society
in Nice. It's very important for German and European activities to have such an excellent
example which the IERS VLBI Technical Development Center developed. We'd like to observe
the Earth rotation parameters by VLBI in near real-time because they are needed for precise
positioning and navigation (e.g. by GPS), for space tracking and also as references for otheron-line observing techniques of the Earth rotation (e.g. laser gyros, supra- uid helium gyros).
Let me inform you, please, that it is intended to develop the real-time capability of the Wettzell
VLBI station in the near future. I hope that these developments could learn from your experiences and real-time VLBI experiments between Wettzell and Japan will be possible, soon.
Working on geodetic VLBI for almost 20 years let me also express my thanks for sending me the
TDC News which is an extremely interesting publication useful for my whole group. I read all
the articles carefully. In particular we are interested on all reports dealing with the broadband
communication between the radiotelescopes and the central processor and those dealing with
automation of the data analysis. Also papers on more general aspects, e.g. reference frames,
Earth rotation are very useful for us.
As the impact of the Key Stone project on the international VLBI activities is considerablylarge I would be very pleased to see these e orts continuing or even growing and I send you
and all the TDC members our best wishes for the future.
Yours sincerely
Harald Schuh(Head of Earth rotation section at DGFI (German Geodetic Research Institute), responsible
for the VLBI group at DGFI)

28

IERS TDC News No.12

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.
Inquires on this issue should be addressed to T. Kondo, Kashima Space Research Center, Communications Research Laboratory, 893-1 Hirai, Kashima, Ibaraki 314-0012, Japan, TEL : +81299-84-7137, FAX : +81-299-84-7159, e-mail : kondo@crl.go.jp.
Summaries of VLBI and related activities at the Communications Research Laboratory are on theWorld Wide Web (WWW). The URL to view the home page of the Radio Astronomy Applications
Section of the Kashima Space Research Center is : \http://www.crl.go.jp/ka/radioastro/".
The URL to view the Keystone project's activity is \http://ksp.crl.go.jp/".

TECHNICAL DEVELOPMENT CENTER NEWS No.12, June, 1998
International Earth Rotation Service - VLBI Technical Development Center News
published by
Communications Research Laboratory, 4-2-1 Nukui-kita, Koganei, Tokyo 184-8795, Japan