TECHNICAL DEVELOPMENT CENTER NEWS No.7
International Earth Rotation Service - VLBI Technical Development Center News

published by

Communications Research Laboratory
4-2-1 Nukui-kita, Koganei, Tokyo 184, Japan
July 1, 1998

CONTENTS

Overview of the Seventh TDC Meeting : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 2

Minutes of the IRIS Subcommission Meeting Held
During the IUGG XXI General Assembly : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 3

Technical Reports
Current Status of the Key Stone Project::::::::::::::::::::::::::::::::::::::::::::::::

5

The Results in the Daily Observation in the Crustal Deformation
Monitoring System in the Tokyo Metropolitan Area : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 6
Real Time VLBI Plan in the Key Stone Project : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 13
Status Report of the CRL 34 m Antenna at Kashima : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 15
The Next Generation Giga-bit VLBI Terminal : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 16
Pulsar VLBI
Kashima(Japan)-Kalyazin(Russia) Pulsar VLBI Experiment in 1995 : : : : : : : : : : : : : 17
UT1 Prediction Improvement Using AAM Datafor Daily VLBI Baseline Analysis : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 19
Atmospheric Path Delay Correction
Based on The Numerical Prediction Data

1:::::::::::::::::::::::::::::::::::::::::::

20

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IERS TDC News No.7

Following special members could not attend:
Nobuyuki Kawano(National Astronomical Observatory), Noriyuki Kawaguchi(National Astronomical Observatory), Teruyuki Kato(Earthquake ReThe Seventh meeting of the Technical Develop- search Institute, University of Tokyo), Hisashi
ment Center was held on September 8, 1995 at the Hirabayashi(Institute of Space and Astronauticalconference room of the Communications Research Science), Yoshimitsu Okada(National Research InCenter.
stitute for Science and Disaster Prevention)

Overview of the Seventh TDC Meeting

Attendance

CRL members

Fujinobu Takahashi, Taizoh Yoshino, Michito
Imae, Hiroo Kunimori, Shin'ichi Hama, Chihiro Miki, Akihiro Kaneko, Toshimichi Otsubo,
Hideyuki Nojiri, Shingo Ohmori(KSRC: Kashima
Space Research Center), Yukio Takahashi(KSRC),
Takahiro
Iwata(KSRC),
HiroshiTakaba(KSRC), Noriyuki Kurihara(KSRC), Ryuichi
Ichikawa(KSRC), Mamoru Sekido(KSRC), Yasuhiro Koyama(KSRC), Yuko Hanado(KSRC) Junichi Nakajima(KSRC), Tadahiro Gotoh(KSRC),
Tetsuro Kondo(KSRC)
Special members

Agenda

1. Opening address by Fujinobu Takahashi, director of the Standards andMeasurements Division, CRL
2. Policy of VLBI technical development
center at CRL
3. Activity reports by the special members
4. Report of IRIS meeting
5. Technical reports
5.1 Keystone project
5.2 Other technical development activities
6. Proposal of R&D experiments
7. Closing address by Shingo Ohmori, director of the Kashima Space ResearchCenter, CRL

Takashi Saito(Geographical Survey Institute),
Teruo Kanazawa(Hydrographic Department, Maritime Safety Agency), Kazuo Shibuya(National Institute of Polar Research),

Key Stone Project (see Page 5). The Key Stone Project is named after a Japanese legendin which a keystone in Kashima Shrine holds down the head of a cat sh believed to cause
earthquakes.

3

October 1995

Minutes of the IRIS Subcommission Meeting Held During
the IUGG XXI General Assembly

The NEOS network is formed by Fairbanks, Green
Bank, Richmond, Hawaii, Fortaleza, and Wettzell
stations. Algonquin and Onsala occasionally join
the NEOS observations. The Intensive operations
are continued using the Green Bank-Wettzell baseline.

Taizoh Yoshino

1.2 IRIS-S

Communications Research Laboratory
4-2-1 Nukui-kita, Koganei, Tokyo 184, Japan(J. Campbell)

IRIS-S is operated once a month with Wettzell
and Westford/Green Bank including the southern hemisphere stations of Hartebeesthoek (South
Date : July 10, 1995 18:00-19:20
Africa), Fortaleza (Brazil). Santiago (Chile) took
part in IRIS-S from mid 92 to mid 93. The frePlace: Engineering Center CR1-7, Uniquency of IRIS-S experiments is low, but they proversity of Colorado at Boulder
vide high precision data owing to extreme baseline
chaired by Taizoh Yoshino (Communicalength for the study of long-term e ects in Earthtions Research Laboratory)orientation.
The correlator at the MPIfR in Bonn is working at the saturation level, the personnel situation
Attendance:
being the limitation. The MkIV correlator will supBrent A. Archinal(USNO) John M. Bosworth plant the present MkIIIA correlator in 1997 ( nan(NASA/GSFC) James Campbell (Univ. Bonn) cial support from IfAG, Geodesy).
William E. Carter (NOAA) M. Cattaneo (University of Genova) Thomas A. Clark (NASA/GSFC) 1.3 IRIS-P (Y. Tamura)
Eva Claudio (University of Genova) Martine Feissel
IRIS-P is not in operation since last year because(Obs. Paris) Dennis D. McCarthy (USNO) Douoflack of funding for correlation time in USNO andglas S. Robertson (NOAA) Harald Schuh (DGFI)
the
problems with operational budgets at several
Bob E. Schutz (University of Texas) Yoshiaki
stations.
Tamura (NAOM) Alan W. Whitney (Haystack
A K4 type single-baseline correlator is runningObs.) Shu-Hua Ye (Shanghai Obs.)
regularly in Mizusawa. It is mainly used for astrophysical purposes, but it has the capability forgeodetic use. A ten-baseline correlator is under
1. Status Reports
construction in the Mitaka headquarters of the National Astronomical Observatory. It is originallydesigned for space VLBI. Hence it does not have
1.1 NEOS (former IRIS-A) and NEOS Inphase calibration. Plans are to modify its hardtensive (D.D. McCarthy)
ware for geodetic applications.
A joint project with China will start soon. A K4
New antennas have been set up at Green Bank, type backend system will be installed at Urumqi
Hawaii and recently in Florida. The latter is a station in China this year.
replacement for the Richmond antenna destroyed
Plans to use the Syowa station in Antarctica arein a hurricane. The clock operations at Richmond still being pursued, although the necessary funding
will be moved to Colorado Springs.
has not yet been secured.
The correlator at USNO is operated for 5 daysa week on two shifts plus a third shift on twodays. This is an increase over the previous situ- 1.4 China (S. Ye)ation, but the number of VLBI experiments that
The Status of the Shanghai Observatory wascan be scheduled by USNO is still limited by the reported with a written memorandum. Several
available correlation time. The funding by NASA experiments of China-Germany-South Africa-Italyof correlation at Haystack has decreased to a very and China-Japan were described. A joint project
low level (only for R&D).
between China and Japan was explained, and a
The VLBI networks of NEOS (weekly) and new IRIS network, named IRIS-E (Eurasia) was
NEOS Intensive (daily) are operated for Earth ro- proposed. (for more detail, see memorandum bytation and polar motion as well as for establish- Ye)ing and maintaining the celestial reference frame.

4

IERS TDC News No.7

(T. Clark)

T. Yoshino: In the Key Stone Project by CRL,
real time data processing connecting four stations
The NASA is conducting global VLBI campaigns via optical ber link is under development.
for plate motion, celestial and terrestrial reference
frames. It carries out R&D work on the further
development of the VLBI DAS and correlator sys- 2. General Discussion
tems. The new MkIV correlator is under development with the cooperation of Haystack and the
The topic of the optimal size of the radio source
JIVE institute in Europe.
catalogue as the realization of the celestial reference system for the geodetic VLBI campaigns was
1.6 Other topics
brought up by Dr. Carter who stressed that thesource list should not be much larger than the 100
M. Feissel (IERS): One copy of the new MkIV or so core sources, and that other purposes (astrocorrelator will be built at Dwingeloo within the nomical research goals on larger samples of geodeEurope-Haystack cooperation in MkIV develop- tically less important sources) should not be supment. It will be used mainly for astrophysics, but ported by geodetic means. Agreement was reacheda smaller share of geodetic work is also possible. on a set of 100 to 200 core sources to be large
Plans are to schedule some European geodetic ex- enough for geodetic reference frame purposes.
periments on the basis of France's nancial contriIn view of the reorganization of the CSTG unbution to JIVE. The correlator is expected to be der Comm.8, a change in the title of the IRISoperational by the end of 1997.
subcommission was discussed. It now seems
T. Yoshino: To monitor the crustal deformation, appropriate to change the title to the "VLBIfour VLBI observation sites are being built in the Subcommission" in accord with the usage for the
Tokyo metropolitan area. The project is named other techniques, e.g. SLR-Subcommission.
Key Stone Project. The system is operated fully
automatically to obtain daily solutions.
H. Schuh: The future of VLBI as a high preci- 3. New president
sion geodetic technique should be ascertained bydeveloping further VLBI technology, aiming at a
All the participants agreed to accept the nomihigh degree of automation and a replacement oftape recording by using wide band communica- nation of Dr. Thomas A. Clark (NASA/GSFC) as
tions links (prospects of real-time VLBI). European the Chairman of the VLBI subcommission under
VLBI group has proposed direct data communica- CSTG for the next four year term.
tion by optical ber network or satellite links.
1.5 NASA/GSFC

5October 1995

Current Status of the Key
Stone Project

Data processing and analysis system

VLBI data are processed and analyzed routinely
at Koganei Central station. New correlator dediNoriyuki Kurihara
cated to the KSP is just about ready for the routine
processing. Presently careful check out comparing
Kashima Space Research Center
the correlation results between KSP and the conCommunications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-0012, Japan ventional one (K3 correlator) tests combining both
hardware and software are going on. We will enter
Development of VLBI stations dedicated to the the routine operation phase of the correlator by the
KSP, which monitors crustal deformation around end of FY1995 (March, 1996).
the Tokyo metropolitan area with a space geodetic technique, started in FY1993. Three of four Future Plans
VLBI stations have already been completed construction. Daily observations on the baseline beReal time VLBI, in which digitized data are
tween Kashima and Koganei have been carried out transferred to the correlator through high speed
since January 1995. The last one will be con- communication link (optical ber) instead of tapestructed during this scal year. Current timetable recording, will be realized on the KSP baselines inof development of each KSP station is as follows. near future.

year
Oct.1995
Dec.1995
Mar.1996

Table 1. Timetable of Each Station's Development
KASHIMA
MIURA
Sub-Center
Data acquisition
Data acquisition
System monitoring System monitoring
Concentrated controlling

KOGANEI
CenterData acquisition
System monitoring
Concentrated controlling

TATEYAMA

Data acquisition
System monitoring

KSP/VLBI system at Koganei station. From left: Weather station, antenna front-end control, calibration
system, backend terminal, and automatic tape loading unit(DMS24).

6

IERS TDC News No.7

The Results in the Daily Observation in the Crustal Deformation Monitoring System in
the Tokyo Metropolitan Area
1

1

1

Y.Takahashi , N.Kurihara , T.Kondo ,1
1
1
H.Takaba , T.Iwata , Y.Koyama ,2

1

1

Y.Hanado , M.Sekido , J.Nakajima ,1
2
2
2
T.Gotou , M.Imae , T.Yoshino , S.Hama ,
2
2
2
2
2
T.Miki , J.Amagai , T.Ootubo ,2

H.Kiuchi , A.Kaneko , H.Kunimori ,2

F.Takahashi

1 Kashima Space Research Center

Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314, Japan
2 Communications Research Laboratory
4-2-1 Nukui-kita, Koganei, Tokyo 184, Japan

1. Introduction

We have established the crustal deformation
monitoring system in the Tokyo Metropolitan Area
(We call this project \KSP"). Both VLBI and
SLR equipment are arranged at the four stations(Kashima, Koganei at HQ in Tokyo, Miura, andTateyama). SLR observations will be conductedalways in the clear sky and 5 hour VLBI experiments will be conducted everyday. The VLBI stations of Koganei and Kashima stations were constructed and we started the VLBI observations between Kashima and Koganei. The rst 24 test experiment was conducted on 29th August in 1994,
and we started 5 hours experiments on every week
day since 31th of January in 1995. As it is in
the period for test experiments now, we conducted
the VLBI observations by 56 Mbps recording mode
which is compatible with Mark-III. The regulardaily 5 hours experiments will be started since thisautumn using 256 Mbps mode on Kashima and Koganei baseline, and the VLBI observations of 3 stations including the Miura stations will be started
at the beginning of next year. Figure 1 shows thecon guration of stations and the results of baseline
length.
The results in the daily test VLBI experimentsfrom 31th January to 6th September (in the period
of about 7 months) are described as follows:(1) The station movement of Koganei against
Kashima station,(2) The change in the correlation amplitude,that is similar to correlated ux density for every
quasar,(3) The comparison of the clock (Hydrogen
Maser).

Figure 1. Con guration of KSP and the baseline length.

7October 1995

Figure 2. Movement of Koganei station against Kashima.

Table 1. Precision and repeatability in KSP test daily experiments.
Mean Precision
Repeatability
Koganei
Position error
Change
(mm)
(mm)
(mm)
(mm/year)Baseline Length
3.2
4.6
60.7
0.561.9
East Movement
3.4
5.2
60.8
-4.462.0
North Movement
4.1
5.5
61.0
16.762.3
Upward Movement 17.0
26.4
63.3
25.569.1

8
2. Station Movements

We developed the software for the baseline analysis, which are called \Takemikazuchi". The software makes the data base and it makes the baseline analysis automatically. This software also supports making the results publically available using
WWW (see Section 7).
Because of the test observations, we make a baseline analysis using the other software \SOLVE"
which was developed by GSFC (NASA), and we describe these results since the repeatability of theseresults is a little better than those by automatic
analysis software.
Figure 2 shows the change in the distance on the
Kashima-Koganei baseline, and the changes in theposition of Koganei (east movement, north movement, upward movement) against Kashima station(when the position of Kashima is xed). Table 1
shows the summary of the precision. For the horizontal movements and baseline length, the precision and repeatability are about 5mm, and theprecision for the vertical movement is about 2.5cm
in spite of the test experiments of 56 Mbps mode.
For the regular experiments of 256 Mbps mode, theprecision will become one third of these results.
The position changes are described in the di erent methods. At rst, one or several stations arexed using the tectonic model, and the positionchanges in the other observed stations are obtained
against the xed stations. This method is useful toobtain the deformation of the observation net. Secondly, the movements are described for the international velocity eld, such as ITRF (International
Terrestrial reference Frame) or the velocity eldof GSFC. Finally, the movements are described as
the displacement from the plate motion. Figure
3 shows the movements of Koganei and Kashima
stations. We also have the results by other experiments, which is call \MDX (Metropolitan Diamond
Cross)". These experiments were conducted among
Kashima 34m antenna, Koganei 3m antenna, and
GSI 5m antenna since 1988 once or twice every
year. We show both sets of results. Figure 3 showsthese station movements. Figure 3-(a) shows the
movement of Koganei station relative to Kashima
station. Figures 3-(b),(c) are the movements of Koganei and Kashima stations for the displacementfrom North American Plate motion in the reference of the GSFC velocity eld in 1993, and in thereference of the ITRF velocity eld in 1993. Figure
3-(d) shows the movements in the reference of the
ITRF velocity elds in 1993. Figure 3-(e) is theplate motion on the plate boundary.
In the Alaska area, the station movements for the
displacement from the North American Plate mo-

IERS TDC News No.7

tion are similar to the direction of the Paci c platemotion on the plate boundary. In the Japanesearea, the movements of the Kashima and Koganei
stations in both KSP and MDX experiments are
similar to the direction of the Paci c Plate motion and the Philippine Sea Plate motion shownin Figure 3-(e). It is possible that the deformation is caused by the pressure of the plate motion.
The movements obtained from KSP experiments
are di erent from those from MDX experiments.
Furthermore, the results appear to di er according
to which velocity eld is used as a reference.
In Japan, many GPS stations and several VLBI
and SLR stations are observed, and the results arecollected. The reference of the velocity eld may
become important.
3.

Change in the correlated ampli-

tudes

In KSP experiments, the correlated amplitudes
are obtained everyday, and we can monitor thechange of the correlated ux density for several
quasars. Figures 4,5 show the change in the meanvalue of correlated amplitudes on the KashimaKoganei baseline for 12 sources at X band and S
band, respectively. The mean value averages thedi erent observations for the resolution and the elevation dependency. In this test period, we do nothave the calibration data, but we can estimate approximately that 0.01about 0.3Jy at S band. Different changes for di erent sources may be causedby changes in the correlated ux density. We canmonitor the continuous variation of the source ux
density for unresolved center part and the burst
change.
4. Comparison of the clock

In KSP experiments, we can monitor the clock.
As we have no information concerning the internal delay in the antenna, the absolute di erenceof clock (Hydrogen Maser) is unknown, but thechange in the clock is observed. Figure 6 shows
the change in the comparison of the clock and thechange in the clock rate. The reasons for the clock
jump is known. The rate change means the stability for long periods.
5. Conclusion

We have conducted 5 hour VLBI experiments forevery week day since 31 January, 1995. Though9

October 1995

these experiments are test experiments in the 56
Mbps mode, we obtain good results and information concerning the practical errors, which are thesame as the theoretical errors. From these results,
we believe that we can achieve 2mm precision forthe horizontal component and baseline length, and
9mm precision for the vertical component in theregular 5 hour VLBI experiments in the 256 Mbps
mode, and these precisions are reduced to half for
24 hour VLBI experiments in the case of real time
VLBI.
The motion of Koganei station relative toKashima station are measured. The movements
are slightly di erent from those inferred from MDX
VLBI experiments. However, the displacementfrom the North American Plate motion is similar tothe direction of the pressure of the plate motion on
the plate boundary. The movements of the other
VLBI stations, at Tsukuba and Kanozan, are also
the same direction.
The indication of the station movements di erens according to the velocity eld that is used as areference. It is important that the reference velocity eld should be common since the comparisonof the di erent analyses and di erent equipment
should be not confused. We also obtain the contin-uous changes in the correlated ux density in KSP
experiments. These changes are useful in characterizing the burst changes of the quasar.
The KSP will be completed in next year, andwe will obtain the positions of 4 stations with theprecision of 2-3mm using daily VLBI and SLR. Furthermore, the real time VLBI using 256 Mbps datatransfer by optical ber cable will be started during
the next year.
6. Announcement

The results of KSP experiments, which are
the station movements and the correlated amplitudes, are made available using the inter-net\WWW". The station movements are the resultsby the automatic analysis software. The reference is the position of the Kashima station movedby the latest ITRF. When you want to see theresults, URL is \http://kouma.crlgo.jp/" in English and \http://kouma.crl.go.jp/index-j.html."
in Japanese. If you have some question about
this service, please ask Y.Koyama in CRL (Emailkoyama@crl.go.jp) or Y.Takahashi (Email takahashi@crl.go.jp).

Figure 3. Movement of Koganei for KSP and MDX experiments and Kashima Station movement.

10

IERS TDC News No.7

Figure 4. The change in the correlated amplitude at X band on Kashima-Koganei baseline without thecorrection.

October 1995

11

Figure 5. The change in the correlated amplitude at S band on Kashima-Koganei baseline without thecorrection.

12

IERS TDC News No.7

Figure 6.The change in the clock between Kashima and Koganei stations.

13

October 1995

On the other hand, nowadays high rate digital
Real Time VLBI Plan in thedata transmission links using optical ber cable
Key Stone Project
are available or under development which have the11Michito Imae , Hitoshi Kiuchi , Tadahiro

2

1

2

Goto , Shin'ichi Hama , Yukio Takahashi ,1
3
Taizoh Yoshino , Hiroyuki Hara , Hisao
3
Uose
1 Communications Research Laboratory

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

2 Kashima Space Research Center

Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314, Japan
3 NTT

transmission rate of several hundred Mbps or exceed 1 Gbps.
The real time VLBI using such a high rate digital communication link will be one of the \breakthroughs" of VLBI to improve the performance andto shorten the duration to output the nal data.
3. Real Time VLBI Plan in the KSP

CRL has been constructing the precise crustal
deformation measuring system in the Tokyo
Metropolitan Area using the space geodetic technique, such as VLBI and SLR, which is called \Key
Stone Project" (KSP) from 1993.
The main target of this project is monitoring thecrustal deformation in mm order level daily for the
study of earthquakes.
For this purpose the real time VLBI, real timereceived data transmission and quick data processing, is being planned in cooperation with NTT(Nippon Telephone and Telegraph Co.), with highrate digital data transmission links among the KSP
stations.
This report describes the concept of the real time
VLBI which is now under construction.

Figure 1 shows the block diagram of the real time
VLBI in the KSP project.
The received signal is digitized by the acquisition system at each station and transmitted to thecorrelation station by using high rate ATM (Asynchronous Transfer Mode) link through the ATM
transmitter.
The transmitted data from each station are combined at the ATM cross-connector at NTT Mitaka
and transmitted to the correlation center locatedat CRL Koganei. The ATM receiver placed at thecorrelation center absorbs the jitter of the ATM
cells and transmission delays using memories.
Each ATM link has the ability of 2.4Gbps transmission rate, but we use the VLBI sampling rate of
256Mbps to keep the compatibility to the recorderbase VLBI experiments.
The correlator which is used in the real time
VLBI is basically a same as the tape-based one,and it has the processing rate up to 512Mbps. After the real time VLBI using 256Mbps sampling
rate technology will be con rmed, we will challenge
higher rate data sampling for the next step.

2. Limit of Recorder Base VLBI and4. The Future of Real Time VLBI

1. Introduction

Real Time VLBI

Development of the VLBI system was made possible by progress in highly stable frequency standards, such as the hydrogen maser, and high speed
digital data recorder. But due mainly to therecording rate of the data recorder, there are several limitations in the VLBI system.
Some of them are
1. receiving band width which is limited by therecorder's recording rate. In the case of K-4 system, 256 Mbps is the maximum recording rate ofthe data recorder.
2. time delay to obtain the analyzed data fromobservation, mainly the need for tape transportation after the observation.

The real time VLBI will be a very powerful solution to improve the VLBI's capabilities. But it
is not the all-round tool, because
1. high rate digital link cost is very expensive,
2. the raw data will be missing without any
backup recording system.
So it is important to consider the real time
VLBI's application eld.
5. Conclusion

The real time VLBI facilities are now under construction for the KSP project, and its rst fringes
will be detected early in 1996.

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IERS TDC News No.7

But the regular base real time VLBI operations
will be started after careful comparison with therecorder base VLBI experiments. The preliminary
data will be presented in the next TDC's news.

Figure 1. Block diagram of the realtime VLBI in KSP project.

15

October 1995

Status Report of the CRL
34 m Antenna at Kashima
Hiroshi Takaba

Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-0012, Japan

1. Antenna Control System

Antenna control unit (ACU) and receive band interchange computer will be replaced to new models
in 1995.
2. Receiver System

1.5 GHz Receiving Syetem
2/8 GHz Receiving Syetem
5/10 GHz Receiving Syetem
15/22 GHz Receiving Syetem
43 GHz Receiving Syetem

Good
Good
Problem on the vacuum of the Dewar. Not available.
A new room temperature LNA is considered to use
for the space VLBI experiment (VSOP).
The receiver noise temperature of the 22 GHz system increases twice.
A new system using an SIS mixer was being tested.

34 m antenna at Kashima

16

IERS TDC News No.7

The High Speed Sampler is designed to sample
The Next Generation Giga-bit
the data rate of 1024/512/256MHz 1/2/4ch 1/2bit
VLBI Terminal
selection. The baseband signal is supplied from1

2

Junichi Nakajima , Hitoshi Kiuchi ,

3

3
4
3
Hideyuki Kobayashi , Yoshihiro Chikada
Sachiko Okumura , Kazuyoshi Sunada ,3

and Noriyuki Kawaguchi

1 Kashima Space Research Center

Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314, Japan
2 Communications Research Laboratory
4-2-1 Nukui-kita, Koganei, Tokyo 184, Japan
3 National Astronomical Observatory
4 Institute of Space and Aeronautic Science

Joint Japanese group (NRO, ISAS and CRL)
have started to develop new VLBI terminals. Thissystem will standardize surprisingly high speed
aquisition (1024M-bits per second) in the near future. To establish high sensitivity in VLBI observations, which enables observations of the weak distant QSO, we must make better use of the receiver
bandwidth. Ground based VLBI is limited by theradio telescope aperture size and the integration
time due to the atmosphere. Development of boththe High Speed Sampler and the High Speed Data
Storage has started. This equipment will be employed as the next Japanese VLBI standard terminal (Fig.1). We will name the system brand new\J-1" or something which indicate the di erence
from the K-4 series.

the NRO wide-band video converter which receive
5 to 7GHz IF optical transmission. The sampler isequipped with the external time code input. Whenthe correlation system needs the time code, it caninsert a user programmable one. We will use theDSO (Digital Storage Oscilloscope) AD-aquisition
module for the sampler. The continuous sampling
DSO provides the function of selection of various
rates and channels. Hence we are using the DSO,
this sampler can monitor the input signals directly.
This is convenient to adjust the signal level. The
sampler applications to the interferometer and thedigital spectrometer components are possible.
The High Speed Storage System will reach the1024Mbits/sec recording. To achieve the rst
ever performance in VLBI, we are modifying the
HDTV-VCR (High De nition TV Video Cassette
Recorder). This recorder is designed for multiHDTV-formats. VLBI raw data is recorded as thepart of HDTV frame data. Error rate is better than
10010 . The recorder time sequence is controlled by
the newly designed VLBI interface. The interface
is arranged to record the data without time code.
Playback speeds of 1/2 to 1/32 are possible for the
low-data rate correlation system. Some of the initial speci cations of the VCR did not reach ourtargets, and we are trying to increase the performance.

Figure 1. 1024Mbps VLBI terminal.

17

October 1995

3. Data processing
Pulsar VLBI
Kashima(Japan)The K3 correlator, developed by CRL, was used
Kalyazin(Russia) Pulsar VLBI for cross correlation processing. First fringes weresuccessfully detected. K3 correlator has a gating
Experiment in 1995
1
2
2
1
1
3
Takahashi , Y. Koyama , Yu. P. Ilyasov ,M. Sekido , Y. Hanado , M. Imae , Y.

3

3

A. E. Rodin , A. E. Avramenko , V. V.

3
4
Oreshiko , and B. A. Poperchenko
1 Kashima Space Research Center

Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314, Japan
2 Communications Research Laboratory
4-2-1 Nukui-kita, Koganei, Tokyo 184, Japan
3 Astro Space Center P.N. Lebedev PhysicalInstitute, Russia
4 Special Research Bureau of the Moscow PowerEngineering Institute, Russia

1. Introduction

Pulsars are high-velocity objects (Lyne 1994)
and their positions and proper motions are important for our understanding of the formation andevolution of pulsars. Accurate astrometric measurements by inter-continental VLBI observation
will determine the positions and proper motions ofpulsars in several years interval observations.
2. Observation and data acquisition

A VLBI experiment observing pulsars and reference sources was carried out by Kashima(Japan)Kalyazin(Russia) baseline in March of 1995.
This experiment was organized by collaboration
between Communications Research Laboratory(CRL) and Lebedev Physical Institute of Russian
Academy of Science (LPI). The antenna diameter and eciency of Kashima and Kalyazin are
34m, 60%, and 64m, 60% respectively. Observation frequency band 1.4GHz was down converted
to video band and divided into 16 channels witheach 2MHz width. Data of each channel are sampled with 4Mbps sampling rate and recorded by
K-4 VLBI recorder. This was the rst VLBI experiment between Kashima and Kalyazin, therefore making sure of the direction of circular polarization, as well as of the coordinates of Kalyazinstation was main purpose of this experiment.

function, which enhance the Signal to Noise Ratio(SNR) of pulsar data by accumulating only a partof the pulsar's signal. Initially we processed thepulsar data without the gating function. Correlation processing with gating function will be donesoon. By using the gating function, weak pulsars,
which have not yet been observed with interferometric methods, will become observable.
4. Preliminary result

A MkIII database, which is used for ordinary
geodetic analysis data storage, was made for pulsar
VLBI data. The analysis software Solve, which is
widely used for geodetic analysis, was used to analyze the position of pulsars. In Fig.1, mark  shows
the result of this experiment and shows the position from Taylor's catalog (J.H.Taylor 1993). The
discrepancies between the results and catalog position may be due to several reasons. The main reason is ionospheric delay: ionospheric delay compensation cannot be done with single band (1.4GHz)
data. Another reason may be the di erence of coordinate systems. Timing positions are relative toa reference frame de ned by an ephemeris of Solar system motions, whereas interferometric positions are relative to equatorial frame de ned by therotation of the Earth to background extragalactic
sources.
5. Future

By applying the pulsar gating function of K3 correlator, SNR will be enhanced and accuracy of theposition will be improved.
This experiment had been organized to analyze
the di erence of delay between pulsars and closest
reference sources (Di erential VLBI). By applying
this method, calibration of ionospheric delay will
be improved.
We are planning to equip K4 backend system
at Kalyazin station for a few years. Then we will
be able to organize pulsar VLBI experiments frequently.
Investigation for how we should compensate theionospheric delay will be necessary. We are considering of using GPS observation for this purpose.

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IERS TDC News No.7

References

Taylor,J.H., Manchester,R.N., and Lyne,A.G., (1993)
Astrophys.J .Suppl., 88, 529-568. "Catalog of 558
Pulsars"
Lyne,A.G., and Lorimer,D.R. (1994). Nature 369,
pp.127-129., "High birth velocities of radio pulsars"

Figure 1. Mark  shows the result of this experiment and shows the position from Taylor's catalog(J.H.Taylor 1993). The discrepancies between the results and catalog position may be caused from somereasons. Main reason may be caused from ionospheric delay because ionospheric delay compensation
cannot be done with single band (1.4GHz) data. Other reason may be the di erence of coordinate .
Timing positions are relative to a reference frame de ned by an ephemeris of Solar system motions,whereas interferometric positions are relative to equatorial frame de ned by the rotation of the Earth tobackground extragaractic sources.

19

October 1995

UT1 Prediction Improvement
Using AAM Data for Daily
VLBI Baseline Analysis
1

2

Jun Amagai , Yukio Takahashi , Taizoh

1

3

Yoshino , and Guo Wei

1 Communications Research Laboratory

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

2 Kashima Space Research Center

Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314, Japan
3 Shaanxi Observatory, Chinese Academy of
Sciences
Crustal deformation monitoring network is under development in Tokyo metropolitan area by
Communications Research Laboratory using VLBI
and SLR techniques. The observation network consists of four stations which are connected by highspeed data transmission network using ATM switch

for the real time VLBI. Precise Earth's rotation parameters, in particular UT1, are needed in time todetermine the baseline vector. The simple method
to predict UT1 from AAM (Atmospheric AngularMomentum) data was investigated and the precision of the predicted value was evaluated.
The error of the UT1 predicted by IERS andthat calculated from AAM data are shown in Fig.1(a) and Fig.1 (b) respectively. Predicted UT1 iscompared with IERS Bulletin-B nal value. The
UT1 prediction derived from AAM data is twice
better than that of IERS Bulletin-A. In this study,
the oldest value in the latest cycle of IERS rapid
data was used for the initial value of integration.
We may have a possibility to improve the precisionof prediction by introducing a more skillful method
such as Kalman lter.
Recently AAM data are calculated by Japan Meteorological Agency within 6 hours. Because theamount of AAM data is very small, it is easy tointroduce AAM data by FTP for quasi-real time
analysis of KSP.

Figure 1. The error of the UT1 predicted by IERS Bulletin-A (a) above and that calculated from AAM
data (b) bellow respectively (Comparison with IERS nal value).

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IERS TDC News No.7

Atmospheric Path Delay Correction Based on The Numerical Prediction Data
ICHIKAWA, Ryuichi

Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-0012, Japan

1. Introduction

Atmospheric path delay is a serious error source
in measurements by very long baseline interferometry (VLBI) both through ray path bending and themodi cation of the electromagnetic wave velocity.
The delay has been separately discussed becauseof its causes; one is the \wet delay" due to thedipole component of water vapor and the other isthe \hydrostatic delay" due to the nondipole components of atmospheric constituents. Geodesists
have especially focused their attention on devising techniques for estimating the wet delay becauseof the signi cant variability of water vapor. Conventionally, the wet delay for each site has been
estimated from a \zenith delay" and a \mapping
function", with the latter function describing theelevation angle behavior of the atmospheric pathdelay (e.g. Chao, 1972; Davis et al., 1985). The
zenith wet delay is estimated from (1) a model
relating surface meteorological conditions to this
delay (e.g. Saastamoinen, 1972), (2) observationby using a ground-based water vapor radiometer(WVR) (e.g. Hogg et al., 1983), and (3) parametric estimation by using a stochastic process suchas the Kalman ltering techniques (e.g. Herring etal., 1990; Tralli et al., 1992). The mapping functions are constructed for a spherically symmetricatmosphere. On the contrary, the atmospheric water vapor, temperature, and pressure vary in various temporal scales and spatial dimensions. Consequently, we exactly require an e ective method tocorrect the azimuthal asymmetry of the wet delay
to attain sub-millimeter accuracy.

Figure 1. Grid system of the JMA (Japan Meteorological Agency) global analysis data. (after
JMA(1995))

from the numerical weather prediction model canbe applied to estimate the wet delay. Figure
1 shows a schematic gure of the global analysis (GANL) data set by the Japan Meteorological
Agency (JMA) (JMA, 1993). The GANL data are
given four times a day to a 1.875-degree latitudelongitude grid system with 16 layers (surface and
15 standard pressure levels, i.e., 1000, 850, 700,
500, 400, 300, 250, 200, 150, 100, 70, 50, 30, 20,
and 10 hPa). At each grid point meteorological elements, geopotential height, temperature, dewpoint
depression, and wind vector are computed fromthe data obtained by radiosonde, aircraft, maritimeand satellite observations, using a multi-variate
optimum interpolation method (Lorenc, 1981) together with the forecast values. Figure 2 shows the
temporal variations of the zenith wet delay basedon the GANL data set and that from radiosonde
observation at Tateno near Tsukuba and Hachijojima in the West Paci c during the period from
April 1988 to February 1989. At both sites thezenith wet delay computed from radiosonde data
varies from 5 to 20 cm in winter (January), andfrom 20 to 40 cm in summer (July). Moreover,
the amplitude of delay variation within the period
2. Atmospheric Path Delay Estimated of several days reaches more than 10 cm during
all seasons. The zenith wet delay based on theby Numerical Prediction DataGANL data set is well consistent with that from radiosonde observations in both amplitude and phase
Recently, the numerical weather prediction through the period. It is clear that the GANL data
model has been successfully used for the pur- set exhibits a good recovery of the observed metepose of the operational weather prediction. The orological conditions. JMA developed ner meshthree-dimensional grid point data set is produced

October 1995

model, named the 10 km spectral model to forecast mesoscale phenomena accurately as shown in
Figure 3. The 10 km data are given on a 97 2
97 latitude-longitude grid system with 10 km intervals (at 60 degrees N) and 12 layers (surface
and 11 signi cant pressure levels, i.e., 1000, 900,
850, 700, 500, 400, 300, 250, 200, 150, and 100hPa) for the purpose of the numerical predictionof mesoscale phenomena of the order of 20-200 km,
such as squall lines, cloud clusters and so on. The

21
outputs from the model can be available to correct
the azimuthal asymmetry of the wet delay. Figure
4 shows an example of positioning errors due to theazimuthal asymmetry of the wet delay numericallyestimated by 10 km spectral model (Ichikawa etal., 1994). Minimum elevation angle of 15 degrees
is assumed. According to the gure, uncertainties
of baseline vectors are up to several centimeters inhorizontal and more than one centimeter in vertical.

Figure 2. Daily variation of the zenith wet delay based on the global analysis data set (solid line) and thatfrom radiosonde observation (broken line) during the period from April 1988 to February 1989 at Tateno(upper) and Hachijojima (lower).

22

IERS TDC News No.7

Figure 3. Forecast area of the JMA 10 km spectral
model.
3.

ProposalofNew

Correction

MethodThe estimations of the wet delay by the numerical prediction data can be easily applied to thecorrection of VLBI measurements considering theazimuthal asymmetry. In the eld of numerical
weather prediction, there has been much e ort recently in developing more accurate models. These
new models are devised to take account of modeling the real atmospheric motion and new meteorological observations such as satellite microwave
radiometry. These model data sets always keep thethree-dimensional scheme. Therefore, once an estimation system of the wet delay is established, we
can easily obtain more accurate estimates of the delay when the numerical prediction model data set
is up to date. This new correction method has two
advantages. First, the equally-weighted correction
to the delay is available wherever the VLBI measurements are conducted. Second, re-examination
and re-correction of the delay for the past geodetic observations are always available by using the
updated model data in the future. It is expectedthat this will become a powerful correction method.
At present, I plan feasibility studies to evaluate theavailability of the numerical prediction data for correcting VLBI measurements.
References

Chao, C. C. (1972): A model for tropospheric calibration from daily surface and radiosonde balloon measurements, Tech. Memo. 391-350, Jet Propul. Lab.,
Pasadena, Calif.

Davis, J. L., T. A. Herring, I. I. Shapiro, A. E. E.
Rogers, and G. Elgered (1985): Geodesy by radio
interferometry: E ects of atmospheric modeling errors on estimates of baseline length, Radio Sci., 20,
1593-1607.
Hogg, D. C., F. O. Guiraud, J. B. Snider, M. T.
Decker, and E. R. Westwater (1983): A steerable
dual-channel microwave radiometer for measurementof water vapor and liquid in the troposphere, J. Clim.
Appl. Meteor., 22, 789-806.
Herring, T. A., J. L. Davis, and I. I. Shapiro (1990):
Geodesy by radio interferometry: The application of
Kalman ltering to the analysis of very long baseline
interferometry data, J. Geophys. Res., 95, 1256112581.
Ichikawa, R., M. Kasahara, N. Mannoji, and I. Naito(1994a): An evaluation of positioning error for space
geodetic technique due to azimuthal asymmetry of
wet troposphere delay based on JMA 10 km spectral
model data, Proceedings of The Eighth International
Symposium on Recent Crustal Movements (CRCM'93), pp. 181-187.
Japan Meteorological Agency (1993): Outline of operational numerical weather prediction at Japan Meteorological Agency, Appendix to Progress Report on
Numerical Prediction Division.
Japan Meteorological Agency (1995): http://www.
goin.nasda.go.jp/GOIN/JMA/htdocs/NPD/
goin npd.html
Lorenc, A. C. (1981): A global three-dimensional multivariate statistical interpolation scheme, Mon. Wea.
Rev., 109, 701-721.
Saastamoinen, J. (1972): Contributions to the theoryof atmospheric refraction, part 2, Bull. Geodesique,107, 13-34, 1972.
Tralli, D. M., S. M. Lichten, and T. A. Herring (1992):
Comparison of Kalman lter estimates of zenith atmospheric path delays using the global positioning
system and very long baseline interferometry, Radio
Sci., 27, 999-1007.

October 1995

23

Figure 4. Estimated horizontal vectors and vertical components of the apparent displacement vectors
caused by the wet delay error due to the azimuthal asymmetry of atmosphere. These apparent displacement vectors are considered to be the relative positioning errors in measurements by VLBI. Minimum
elevation angles of radio sources are assumed to be 5 degrees. Frontal position is obtained from JMA
operational surface analysis.

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IERS TDC News No.7

In October 1990, the International Earth Rotation Service (IERS) designated the Communications
Research Laboratory (CRL) and Haystack Observatory, USA, as the Technical Development Centers(TDC). These centers are 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 planof 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, Kashima Space Research Center, who is the current representative of TDC at the Communications Research Laboratory, Japan. The editor wishes to thankDr. 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 the Kashima Space Research Centeron the World Wide Web (WWW). The URL to view the home page is : http://apollo.crl.go.jp/

TECHNICAL DEVELOPMENT CENTER NEWS No.7, October, 1995
International Earth Rotation Service - VLBI Technical Development Center News
published by
Communications Research Laboratory, 4-2-1 Nukui-kita, Koganei, Tokyo 184, Japan