Technical Development Center News No.1

(International Earth Rotation Service
VLBI Technical Development Center News)
October, 1991

(Reproduced in June, 1998)

Introduction
Contribution of the Japanese technology
for the International Earth Rotation Service

Akira Sugiura
ChairmanCommittee on Space-Time Measurement ProjectGreat progress has been made in the science and space geodesy during the past decade. In thesecircumstances the International Earth Rotation Service (IERS) started its activities in precise observations of the Earth rotation. This work requires a variety of advanced technology, such as Very Long
Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Lunar Laser Ranging (LLR) and Global
Positioning System (GPS). These sophisticated observation systems have greatly changed our views of
the nature of Earth so far. For further extending our scienti c knowledge, it is believed essential todevelop and improve the technology of observation systems . Therefore, the IERS designated our laboratory (CRL) and Haystack Observatory (in USA) as the VLBI Technical Development Centers (TDC)in October 1990. It is a great pleasure for us to contribute to the IERS in the technical elds as wellas in the experimental ones. We will make every possible e ort to improve the relating technology incooperation with other laboratories in Japan.

Establishment of VLBI Technlcal Development Center
Technical Development Center (hereafter TDC) will work
I. to develop new observation technique and new system for more advanced Earth's rotation observation by VLBI and other space technique,II. to promote the research of Earth's rotation by supporting the VLBI technology level,
andIII. to distribute new technology of VLBI.
The TDC not only develop new observation system, but also make e orts to apply the products toenhance the knowledge of human being through RD experiments and exchanging scientists.
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IERS TDC News No.1

Organization
Location of the TDC in IERS is shown in Fig.1. In Japan, three Centers are working for IERS,
which are VLBI observation center (NAO), analysis center (NAO) and TDC. TDC is organized by
the Director General of Communications Research Laboratory. And it is managed under the SpaceTime Measurement Project Committee. The President of the Committee is Director of the Standards
and Measurement Division, who designate the members of the Comittee. Moreover, Director Generalrequests the special members from the other institutes. The Committee is to be advised concerning theplan of Technical Development by the special member.

Management
TDC chooses the development themes for the future IERS activities. And technical development
plan is made in the TDC meeting. Selected theme is studied both in CRL and at other relating
study groups. And technical information is exchanged with the other TDC (Haystack Obs.) for theinternational cooperation.

Figure 1. IERS ORGANIZATION.

October 1991

3

First TDC Meeting was held

July 25, 1991 at the Conference Room of CRL
Agenda

1. Opening
Dr.R.Hayashi, Deputy Director General, CRL
Mr.A.Sugiura, Director of Standards and Measurements Division, CRL
2. Introduction
Mr.K.Uchida, Director of Kashima Space Research Center
3. Remarks for the TDC program by the special members
4. Organization and Role of the TDC
5. Technical Development Plan
(1) K-4 system(2) Millimeter Wave VLBI
(3) Antarctic VLBI
(4) Utilization of Satellite Technique
6. Discussion on the plan for 1990 chaired by Dr.T.Yoshino
Minutes

F.Takahashi : A number of items for deveIopment are shown. Priority of the development should be discussed.
Suggestions for the development plan are welcome.
Kawaguchi: I hope TDC will develop VLBI observation technique in higher frequency band.
Ejiri: Toward the regular VLBI experiment in Antarctica, cooperation between NIPR and TDC is expected.
Nakahori: Since 1981, GSI has been cooperating with CRL to conduct domestic VLBI experiments. We hopethese activity will grow and realize the system for the mean sea level measurement. We are now trying to
reduce the error of vertical component at the observing station with schedule optimization.
Kawaguchi: I would like to know the current status of the development plan of data processor for the Earthrotation observation.
F.Takahashi: For the VLBI experiments, we observe with Mark III type DAT in international experiments andwith K-4 type DAT in domestic experiments, in most cases. At the moment, data processing for international
VLBI experiments is dependent on the correlator in the USA and Germany, while data by domestic experiments is processed by K-3 type correlator in Japan. We are developing the K-4 type correlator to make thebest use of its advanced functions.
Kawaguchi : It is planned to develop a new correlator for 20 stations at NAO (Mitaka, Tokyo). Geodetic
application is also taken into account in the design of this correlator. For K-4 correlator under developmentin CRL, what is the relation with Mark IV?
F.Takahashi: Mark IV is under development. We have to complete the K-4 system.
Okihara: As a future VLBI recorder, data recorder with helical scan type is very promising. Furthermore, thecost of the K-4 type data recorder will certainly decrease.
Manabe: I am afraid that the data quality of Kashima station with Mark III HD recording is not good enough.
I hope it will be recovered soon . The most important item must be K-4 correlator development. And I prefer
the data processing system which is capable of correlation with mixing the K-4 type data and Mark III type
data.
Murata: CRL has unique opportunity to have both VLBI and SLR facility. And CRL has conducted VLBI
technical development. I hope CRL will make more e orts for the SLR development. And I suggest introducing
the SLR analysis software for the ecient development.

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IERS TDC News No.1

Manabe: What kind of computers will be used for the data analysis?
Y.Takahashi: They are HP-IOOO, micro VAX, and FACOM main frame computers.
Sengoku: I hope CRL will make e orts for the collocation experiment with VLBI and SLR to establish reference
frame.
Kawaguchi: Are there any plan to commercialize Hydrogen maser? And I hdpe TDC will develop compact andstable oscillator which is also applicable to transportable VLBI station.
Nakayama: We can contribute to TDC with the integration of many technical aspects.

Attendees :Risao Hayashi
Akira Sugiura
Fujinobu Takahashi
Taizoh Yoshino
Hiroo Kunimori
Kuniaki Uchida
Michito Imae
Tetsuro Kondo
Yukio Takahashi
Hitoshi Kiuchi
Hiroshi Takaba
Seiji Manabe
Noriyuki Kawaguchi
Yoshiro Nakabori
Arata Sengoku
Masaaki Murata
Masaki Ejiri
Daishiro Okihara
Makoto Nakayama

CRL/Tokyo
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
JHD
NAL
NIPR
SONY
NEC

Abbreviation:
CRL:
NAO:
GSI:
JHD:
NAL:
NIPR:

Communications Research Laboratory
National Astronomical Observatory
Geographical Survey InstituteHydrographical Survey Department
National Aerospace Laboratory
National Institute of Polar ResearchOctober 1991

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Technical Topics

In every issue of the TDC News, topics of technical development is introduced by the researcher in
TDC.

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IERS TDC News No.1

Status report of the system developing group

byH. Kiuchi

The K-4 system

In the Very Long Baseline Interferometer (VLBI), the radio emission from a radio source several
billion light years away is received by two stations and the distance between the two stations can be
determined with an accuracy of 1-3 cm by measuring the slight di erence in arrival times of the signals
at the two stations. As the received radio wave is very weak, it is necessary to integrate a very large
amount of data. Hence, it is necessary to record a large amount of observational data. A high-recording
density high-speed large-capacity data recorder is therefore one of the most important parts of the VLBI
system.
The K-4 VLBI system is being developed at CRL as the next-generation system. In this system arotary-head cassette recorder (American National Standard 19 mm Type ID-1 Instrumentation Digital
Cassette Format) is used to make the system smaller and easier to operate. The interfaces are designed
to be compatible with that new recorder. Two interface units are used to obtain compatibility withother VLBI equipment: an input interface unit between the video converter and the recorder and an
output interface unit between the recorder and the data processing system. We are making a morecompact system with observational functions and data processing functions housed in separate units.
The K-4 system consists of the following; (1) local oscillator. (2) video converter, (3) input interface
unit, (4) output interface unit (5) data recorder.
The block diagrams are shown in Figs. 1 and 2. The local oscillator synthesizes the local frequency
signal for the video converter. The video converter converts a window in the IF signal (lOO-500 MHz)input to a video signal (0-2 MHz). The frequency conversion is achieved by the image rejection mixer
using single-sideband conversion. These functions are equivalent to the IF distributor, video converters(16ch) and reference distributor of the Mark-III or K-3 VLBI systems.
The input interface unit is used for data acquisition and recording at the VLBI observing station(Fig. 1). It samples the video signal from the video converter, and sends the digital data to the data
recorder together with the time data which is derived from the external time standard signal.
The output interface unit is used at the correlation station (Fig. 2). It converts the reproduced data
into the appropriate output format, and sends them to the correlator. The format of the output interface
unit is compatible with the Mark-III format. Besides this format, another format is also provided for
future correlator systems; this provides only digitized raw data signals. When multi-baseline correlation
is processed, all the output interface units are daisy-chained through GPIB, so that the tape position
data and status data of all the data recorders can be exchanged. The main (reference) output interface
supplies the timing clock to sub-output interfaces. The delay bit between the main and sub-output
interface units is calculated in each sub-output interface unit, using the time data which is periodicallyinserted into the recorded data.
It is possible to interface with current VLBI systems through the above-mentioned two interface
units. Input and output interface units, when connected together directly, also perform a function
equivalent to the formatter of the K-3 VLBI system.
Due to the development of technology, VLBI is now used for more varied purposes and its observing
stations are not only xed ones but mobile ones used in remote islands and in Antarctica

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October 1991

Figure 1. Observing station.

Figure 2. Correlation station.

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IERS TDC News No.1

Geodetic VLBI experiment at 22GHz band

Yukio TAKAHASHI

Current geodetic VLBI experiments are conducted in S/X band. Improvements of precision aredesired in the geodetic VLBI. The geodetic VLBI in 22GHz is the one of the solution to this demand,
because of following reasons;(1) The observation bandwidth can be expanded easily. The precision of geodetic VLBI is inversely
proportional to the bandwidth.
(2) Ionospheric delay in 22GHz band is smaller than one in X band. The ionospheric delay will becorrected using GPS equipment. All video channels are used for only 22GHz band, so SNR canbe improved(3) Tipping data of the same antenna will be obtained the water vapor data as WVR (Water Vapor
Radiometer).
(4) The precision of delay rate becomes better since it is inversely proportional to the observation
frequency.
The geodetic VLBI needs the phase calibration (PCAL) data for each channel in the observation
band. CRL developed a new PCAL equipment in 22GHz band. At 16th February, the geodetic VLBI
experiment in 22GHz band was conducted between the Institute of Radio Astronomy (Bologna, Italy)
and CRL (Kashima, Japan). The purposes of the experiment are(1) to check of the new PCAL equipment for 22GHz in the international geodetic VLBI experiments,(2) to obtain the basic data of the radio sources and the baseline analysis.
In this experiment, 240 observations were conducted for 40 radio sources. We succeeded in theexperiments, band width synthesis and baseline analysis. The r.m.s. values of delay and delay rate
residuals were 183ps and 94fs/s respectively. The r.m.s. values were almost the same as the r.m.s. value
in standard geodetic VLBI experiments in S/X band because we did not use wide band receiver thistime and ionospheric delay corrections. The information of the sources in 22GHz band, such as thecorrelation ux and the resolution, were obtained on the long baseline (8000km). The relation between
the distance (z) and the correlation ux density. The new method to estimate the coherence loss by theatmospheric scintillation is proposed. The data will be useful for the future geodetic VLBI experiments
in 22GHz band.

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October 1991

Precise Ionospheric Delay Corrections by GPS for VLBI
Geodetic Measurements Made at a Single Frequency Bandby Tetsuro KONDOIn VLBI geodetic measurements excess delays caused by the charged particles existing along theray paths from a radio star to each antenna, mainly due to the di erence in the terrestrial ionospheric
total electron content (TEC) along each ray path, are corrected by receiving dual S(2GHz) and X(8GHz)
frequency bands. This dual band receiving system, however, makes it dicult to employ a small antenna(less than 3 m in diameter) for a VLBI remote station in spite of the merits of small antennas such as
low cost of construction and ease of transportation. On the other hand the GPS signal measurement
provides an independent measurement of the TEC applicable for calibration of the excess delays incase of VLBI measurements made at a single frequency band. Consequently the antenna size can bediminished. The directions of GPS satellites from a station are, however, usually di erent from those ofradio stars observed by VLBI. Hence the TEC obtained by GPS measurements have to be mapped toany other directions. S ome models have been proposed as mapping methods on the basis of assumptionof the spherical-shell-like and static ionosphere. Simultaneous observations of dual-band VLBI and of
GPS enable us to evaluate models, i.e., we can assess validity of each mapping model through a directcomparison of TECs (or excess delay time at same frequency) obtained by both observations. We havealready made this kind of observations several times. According to a preliminary result, some mapping
model shows coincidence between VLBI and GPS measurements less than 0.18 nsec at 8 GHz. Now
mapping method is being re ned to accomplish much better coincidence (<0.1 nsec : requirement froma geodetic VLBI).

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IERS TDC News No.1

The evolutlon of water maser spectra in M type stars

Hiroshi Takaba, Radio Astronomy GroupA portable acousto-optical spectrometer (AOS) became available at Kashima. The AOS uses an optical diode laser and had been developed in Nobeyama Radio Observatory (Miyaji 1991). The frequency
resolution and the total band width are 40 KHz and 40 MHz, respectively. The AOS is used to checkthe pointing at the VLBI observation time of maser sources. A new automatic maser survey software
was developed by the author and a snapshot 22 GHz H2 0 and 43 GHz SiO (J=1-0,v=1) maser survey
was made between 1991 April 26 and May 11 using the AOS and with 34 m radio telescope at Kashima.
About 200 stars were selected from the catalog of stellar masers by Benson et al. (1990) and about 160
late type stars were observed almost simultaneously with both two maser transitions.
By comparing those spectra, a systematic change of H2 0 maser spectra was found in M type stars. In
gures' 1-3, H2 0 and SiO (J=1-0,v=1) maser spectra toward three stars (a visible Mira variable R LMI,a near infrared source IRC+60169, and a far infrared source OH12.8-1.9) are shown. Double peaked
H2 0 emissions are seen in IRC/AFGL objects and OH/IR stars and as shown in gure 4, the expansion
velocity of the H2 0 maser is found to be correlated with the IRAS color temperature derived from 12
m and 25 m intensities.

H2 0 (Top) and SiO (Bottom) maser spectra of R LMI ( Fig. 1), IRC+60169(Fig. 2) andOH12.8-1.9(Fig.3)
The oxygen-rich M type stars are thought to evolve in the sequence of Mira variable, IRC/AFGL
objects, and OH/IR stars. In this evolutionary sequence, the mass-loss rate increases and the IRAS twocolors (12m and 25m) becomes cooler (e.g., Van der Veen 1989, Bowen and Willson 1991). Therefore
our result shows that the H2 O maser emitting regions are expanding from the star with the evolutionof the central star. Since Cooke and Elitzur (1985) calculated that the location of 22 GHz H2 0 maser
emitting region moves out with the mass-loss rate increase based on the collisional excitation model,
our observational result is simply explained by the collisional excitation model. Thus we can say ourobservation is a strong evidence of the collisional excitation of 22 GHz H2 0 maser in late-type stars.
We are planning VLBI observations with KNIFE (Kashima Nobeyama Interferometer) for moredetailed study of stellar masers in this and early next year.
References

Benson, P.J. et al., 1990. Ap.J. (Suppl), 74, 911.
Bowen, G.H. and Willson, L.A., 1991, Ap.J. (Letters), 375, L53.
Cooke, B. and Elitzur, M., 1985, Ap.J., 295. 175.

October 1991

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Miyaji, T., 1991 in preparation.
Van der Veen, W.E.C.J., 1989. Astr. Ap., 210, 127.

Figure 4. Plot of the H20 maser velocity width (half intensity width for single peaked sources anddi erences between two peaks for double peaked sources) versus the IRAS two color ratios.

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IERS TDC News No.1

Determination of global position at Tokyo SLR station
Hiroo Kunimori

Satellite measurement group composed of members in frequency and time measurements section,
CRL, have been developing satellite laser ranging (SLR), GPS time receiver and two-way INTELSAT
time transfer techniques. With regard to the development of VLBI, we would o er evaluation measuresof accuracy in geodetic and time comparison results. We would also contribute the construction of IERS
reference frame by their collocation with VLBI.
In January 1990, CRL's new satellite laser ranging (SLR) facility with a l.5m diameter telescope atTokyo has started the observations to the major laser satellites. It participated in intensive tracking
campaign for Russian satellite, ETALONs, during a period from September to November in 1990.
From this campaign, global position of Tokyo SLR station is determined with the precision of several
centimeters. The di erence of coordinates between SLR and VLBI at Tokyo SLR station are less than 10
cm. Fig.1 shows positions of Tokyo SLR station (CRLLAS) and Kashima VLBI station. Fig.2 presents
the estimated precision for each stations during ETALON campaign.

Figure 1. Position of Tokyo SLR and Kashima VLBI station.

Figure 2. Precision estimated from ETALON1 5 min normal points for each station during ETALON
Campaign Sep-Nov,1990.

October 1991

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IRIS President from CRL

During the XXth IUGG Conference in Vienna (August, 1991), the IRIS steering committee washeld. It is decided to propose to CSTG that Dr. Taizoh Yoshino of CRL follows Prof. James Campbell
as the president of subcommission IRIS for the next four year term.

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 to
the following address.
Taizoh Yoshino
IERS VLBI Technical Development Center
Communications Research Laboratory
Nukui-kitamachi 4-2-1
Koganei, 184 Tokyo
JAPAN(FAX) +81-423-21-9899(MarkIII) CRL(Internet) yosh@frex.cc.crl.go.jp