Technical Development
Center News No.2
(International Earth Rotation Service
VLBI Technical Development Center News)

published byCommunications Research Laboratory
in Tokyo, JapanApril, 1992

(Reproduced in June, 1998)

Introduction

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

12IERS TDC News No.2

The Second TDC Meeting was heldon February 28, 1992 at the Conference Room of Kashima Space Research Center (CRL).

Agenda
1. Opening, by Mr.A.Sugiura, Director of Standards and Measurements Division, CRL
2. Report on the Technical Developments in 1991
(1) Outline(2) K-4 System Development(3) Earth Rotation Observation(4) Geodesy(5) Millimeter Wave VLBI and Radio Astronomical Aspects(6) Utilization of Satellite Technipues
3. Discussion on the report
4. Discussion on the proposal about the Antarctica VLBIMINUTES OF THE MEETING
Kawaguchi:
Hama:
Okihara:Kawaguchi :Nakayama:
Uchida:Kawaguchi:

Nakahori:

Is it really possible to have 32 MHz bandwidth in the sideband of Video Converter ?
It is planned, and is under development.
Regarding the K-4 data recorder, GP-IB is available as well as RS422 interface.
Moreover VME bus and SCSI interface are also available in near future. Socontrolling the K-4 data recorder will be easier by making use of a variety offunctions.
I hope 22GHz band receiver will be also included at the Antarctic station in
Syowa for the future VLBI.
Loss in the radome and surface accuracy of the 11m dish have to be taken intoaccount. I think it is technically possible.
What is the di erence between K-4 and new K-4?
It has been a rule that new number (one digit) is given for a system when
we introduce a new type data recorder in it. But to distinguish a system byversion number (more detail) must be necessary after signi cant modi cation
to avoid confusion.
We are analyzing the long and short tidal terms to distinguish the mean sea
level change from the tidal e ects. These results will be taken into accountwhen we evaluate our VLBI data.

Following the above discussion, a topic concerning the promotion of a VLBI project in the Syowa
station was discussed. Discussions about this topic are also shown below.
Finally, it was suggested that the policy of VLBI development should be discussed between bothTechnical Development Centers in the United States and Japan. We will try to nd an e ective way forthis purpose.

3April 1992

Discussion on the Resolution proposed by Prof.

Ejiri about Promoting theVLBI project in Syowa station

Ejiri:(He explained the meaning of his proposal. See the attached proposal (notincluded in this issue reproduced in 1998!).)Kawaguchi: I agree with the meaning of the proposal. But why does the TDC make sucha resolution?
Uchida:We can endorse the plan from the technical point of view. I suggest to stress
the technical points in the proposal.
Sugiura:I think the endorsement should be made also from the Japanese committee ongeodesy.
Ejiri:
It takes time. But I should try.
Sasao:
I will also try to get an endorsement at the Japanese committee on astronomy.
Attendees:

Abbreviation:

CRL:
NAO:
GSI:
NIPR:

Akira Sugiura
Fujinobu Takahashi
Taizoh Yoshino
Hiroo Kunimori
Kuniaki Uchida
Michito Imae
Shin'ichi Hama
Yukio Takahashi
Jun Amagai
Hiroshi Takaba
Tetsuo Sasao
Noriyuki Kawaguchi
Yoshiro Nakabori
Masaki Ejiri
Daishiro Okihara
Makoto Nakayama

Communications Research Laboratory
National Astronomical Observatory
Geographical Survey InstituteNational Institute of Polar Research

CRL/Tokyo
CRL/Tokyo
CRL/Tokyo
CRL/Tokyo
CRL/Kashima
CRL/Kashima
CRL/Kashima
CRL/Kashima
CRL/Kashima
CRL/Kashima
NAO/Mizusawa
NAO/Nobeyama
GSI
NIPR
SONYNEC4

IERS TDC News No.2

IERS VLBI TDC Resolution
28 February 1992RESOLUTION FOR PROMOTING VLBIAT SYOWA STATION IN ANTARCTICA

The Committee on VLBI Technical Development Center (TDC) in Communications
Research Laboratory (CRL) under International Earth Rotation Service (IERS),CONSIDERING,(a) that Japan conducted successfully the test VLBI experiment in Antarctica in January, 1990, whose results are of great contribution to the international VLBI community,(b) that it is, however, still under planning phase to prepare the necessary equipments
for the regular VLBI experiment at Syowa Station,(c) that Germany has recently constructed the VLBI systems at O'Higgins in Antarctica, and the USA is planning to develop the VLBI station in Antarctica,(d) that Syowa Station is expected to play an essential role in Antarctica VLBI,(e) that IERS understands the importance of- precise earth's rotation observation by global VLBI network including Antarcticregion,- establishment of the terrestrial reference frame especially in the southern hemisphereincluding the Antarctica,- establishment of the celestial reference frame including the radio sources in thesouthern hemisphere,and- monitoring the global environments including the atmosphere and oceans in Antarctica,
UNANIMOUSLY RESOLVES

that the following actions should be urged,(1) that the institutions and organizations conducting IERS VLBI program make every
e orts to promote the construction of a VLBI facilities in Antarctica,(2) that the regular VLBI experiment will be started urgently at Syowa Station inAntarctica among the international VLBI network.

5April 1992

Technical Topics
In each issue of the TDC News, topics of technical development are introduced by researchers ofTDC.

Tokyo SLR Station

6IERS TDC News No.2

Status Report of the System Development Groupby Shin'ichi HAMA
1. New K-4 Input Interface
New K-4 VLBI input interface which has multi-bit sampling capability, is under development. Input
interface corresponds to the formatter in Mark-III system. Fig.1 shows its block diagram. Sampling in
1, 2, 4 and 8 bits is possible. The number of channel can be 1, 2, 4, 8 or 16. As the total bit rate is
256Mbps, the bandwidth of each video channel depends on their combination, though video bandwidth
wider 20MHz is not easy to achieve. It is planned to have a complete version in 1993. The system is tobe used for VSOP (Space VLBI in Japan) and IRIS-P experiments.

2. K-4 Correlator
The K-4 data processor is not for routine process but for R&D experiments such as multi-bit sampling, detection of milli-second pulsar timing. And it will be a test version of the correlator for regular
VLBI including IRIS-P. Test model of K-4 correlator is being developed by making use of LCA (FPGA
produced by Xilinx Co.). It is a simple one unit correlator but can process 2 bit sampling data.

Figure 1. New K-4 Input Interface with Multi-Bit Sampling.

7April 1992

Earth Rotation Observation and other Current Topics

by Yukio TAKAHASHI
1. Status of Earth Rotation Observations
The regular VLBI experiments (IRIS-P) have been conducted every month for the earth rotation
observation. However, the high density head of the MarkIII type data recorder in Kashima got aserious problem last year. It was repaired by Haystack Radio Observatory, and Kashima started IRIS-P
observation again since January 1992. We will stock the high density head in the National AstronomicalObservatory.
We will participate in the intensive VLBI experiments this summer which are proposed by USNO,
because we have been making e orts to undertake such intensive VLBI experiments since several years.
The test experiment was already conducted on March 10.
CRL and NAO discussed the possibility of observation in IRIS-P network by K-4 system and alsowith Mark-IIIa system in order to conduct the more frequent observation (weekly) and intensive VLBI
together with the other IRIS network and NAVNET.

2. Other Toprcs
2.1 VLBI Experiments with the Syowa Station in Antarctica
VLBI terminals of Syowa Station were set up not permanently but temporarily in the rst experiment (1990). CRL provided technical suggestions to the National Institute of Polar Research for thepermanent VLBI system at Syowa Station, such as H-Maser frequency standard, Receiver system, K-4
data acquisition terminal and the check system at Syowa station.

2.2 Absolute Sea Level Monitoring by Space Geodetic Techniques
We have developed a transportable VLBI station for the absolute sea level monitoring in cooperation
with Geographical Survey Institute (GSI) under the auspices of Environment Agency. The 2.4m antennasystem, which is the smallest for VLBI, was already developed with only X band receiver. If we observe
the Total Electron Content by GPS receiver such as TECMETER developed at CRL during VLBI
observation, we can reach almost the same precision as with the dual frequency observation by increasing
the number of observations. We will start the mobile VLBI experiment this year.

2.3 Geodetic VLBI Experiment at 22GHz
A new type Phase Calibration equipment for 22GHz band was developed at CRL. And it was applied
for the geodetic VLBI experiment in the 22GHz band which was conducted at 16th February in 1991, incooperation with Institute of Radio Astronomy in Bologna University (Italy). We obtained the fringes
at 22GHz band for a 8000km baseline using 40 quasars. And we made a baseline analysis.
We also estimated the coherence loss caused by the atmospheric scintillation using a phase calibration
signal. It is applicable for estimating the amplitude of the radio sources. It implies the importance ofthe Phase Calibration signal for the astronomy in 22GHz band.

2.4 Di erential VLBI Technique
CRL and NAO are developing new di erential VLBI technique using 34m and 26m antenna inKashima, and 45m and 6m in Nobeyama. The in uence of the instability of hardware and atmosphericscintillation can be canceled out more precisely than the usual di erential VLBI to change the antennapair. The precise source position will be also obtained, and the phase delay may be useful to improve
the precision of the geodetic VLBI. (See the following Figure)8IERS TDC News No.2

9April 1992

The Space VLBI Project using ETS-VI

byTakahiro IWATA
Space VLBI experiment is scheduled using ETS-VI geostationary satellite. Japan's Engincering Test
Satellite VI which will be launched in 1993. Fig.1 shows the schematic block diagram of the experiments.
VLBI observations on the satellite will be made with the 19-element of 34 cm diameter phased array
antenna at 2.3 GHz. Received data at the satellite and frequency standard signals at the ground station
will be transmitted between the satellite and the 5 m diameter antenna of the Ka-band feeder linksystem at Kashima Space Research Center. Experiments for the real time fringe monitoring system will
be made using the imitated radio star signals which will be emitted from the S-band imitated satellite
station at Kashima Center. These experiments with technologies of data and frequency standard signaltransmissions will take the initiative in future space VLBI observations.

Figure 1. A schematic block diagram of the space VLBI experiments using ETS-VI.

10IERS TDC News No.2

IONOSPHERIC DELAY CORRECTION IN SINGLE BANDVLBIMODEL IMPROVEMENTby T. KONDO
Total electron content (TEC) measured by dual band GPS receiver can be utilized for calibrationof ionospheric excess delays of geodetic VLBI when observations are made at a single frequency band.
A key point in realization of ionospheric delay correction is how well TEC measured for GPS direction
is mapped to radio star direction observed by VLBI. We have developed a two step mapping method:at rst distribution of vertical TEC (VTEC) on a time(UT)-latitude plane at a station is estimatedfrom TEC measurements (Fig.1), then VTEC is mapped to a desired radio star direction. This process
is carried out at each station. By di erentiating TECs mapped to a star direction, we can obtain an
ionospheric correction for VLBI data analysis. The results is evaluated by comparing actual ionosphericcorrection observed by dual frequency band VLBI and that calculated from TEC measured by GPSreceiver. As demonstrated in Fig.2, a good coincidence (SD < 0.1nsec) is obtained in an elevation angle
range larger than 20 degree. By taking horizontal density gradient into a mapping model, tting could
be improved.

Figure 1. An example of VTEC distribution. Unit is
1O16 electron/m2 .

Figure 2. Comparison between ionospheric corrections (abscissa: observed by dual band VLBI, ordinate:calculated from GPS TEC).

11April 1992

Development of Space Geodetic Technology Analyzer,
CONCERTO : The First Phaseby Hiroo KUNIMORI
Communications Research Laboratory (CRL) has made SLR obsefvation and has taken the data since1990. We are now engaged in development of a unique analysis software for SLR, named "CONCERTO"(Computalized satellites' Orbits aNalyzer by CRL spacE and time Research Group in TOkyo) on Sun
SPARC workstation.

Figure 1. Structure of CONCERTO.

Numerical standards and algorithm used in CONCERTO are consistent with VLBI analyzer in CRL
Kashima. CRL is one of institutions which have both SLR and VLBI observation systems. Though eachof the two geodetic methods has attained very high precision, it is dicult to verity their own accuracy.
The models and constants in the VLBI analyzer and CONCERTO mostly utilize IERS Standards tocompare the results from each other working with a model switcher and databases. It is used for laser

12IERS TDC News No.2

ranging analysis such as collocation experiment with VLBI and at present it can be handling with small
data volume and number of stations. The functions of CONCERTO are orbit prediction of geodeticsatellites orbits, and solution of geodetic parameters.
The functions of modules in CONCERTO are as follows :MAIN: Supervise whole programs.
ACCEL: Calculate the modeled accelerations that in uence to satellite.
EARTH: Calculate the position of the observation site in J2000.0 reference
frame.
RCALC: Output the range prediction, using results of two modules above.
PART: Prepare the partial derivatives by parameters.
SOLVE: Determine the set of parameters by means of least squares method.
OBSDAT : Access the SLR observation data les.
DBASE
: Access the data les of physical constants, earth rotation parameters, and so on.
Figure 1 shows the structure of CONCERTO. The blocks marked with \#" are modules underdevelopment, ones with \*" have been completed. The other modules will be programmed soon. Figure
2 shows the \O - C" ([observation range value] - [calculated value by CONCERTO]) plot of LAGEOSI 09/24/91 pass. The initial position and velocity vector of the satellite are estimated by software`UTOPIA' developed in Center for Space Research of University of Texas at Austin.

Figure 2. \O - C" plot of range for LGEOS I orbit on 09/24/90 (integration begins at UTOh).

13April 1992

The TDC News is published biannually. To begin or discontinue the receipt of the TDC News, please
send a message to the following address. Comments, questions and /or suggestions can be also sent tothe following address.
Taizoh Yoshino
IERS VLBI Technical Development Center
Communications Research Laboratory
Nukui-kitamachi 4-2-1
Koganei, 184 Tokyo
JAPAN(FAX)(MarkIII)(Internet)+81-423-21-9899
CRL
yosh@frex.cc.crl.go.jp