ISSN 1882-3432

CONTENTS
Proceedings of the 11th NICT TDC Symposium (Kashima, February 23,
2012)
A Plan of the Automatic Observation System for the Tomakomai 11-m Radio . . . . . . 1
Telescope
SORAI Kazuo, MINAMIHARA Noriyuki, MOTOGI Kazuhito, OHISHI Yukie,
HIURA Koichiro, UMEI Michiko, SEGAWA Yoko, TASHIRO Takami,and
SEKO Akifumi
Hope on GHz-band width signal recording and 100 k-channel spectroscopy . . . . . . 3
for VLBI imaging of astronomical maser sources
Hiroshi Imai

Proceedings of the 12th NICT TDC Symposium (Kashima, June 6, 2013)
Present Status of Ibaraki station (Takahagi and Hitachi 32-m Radio Tele- . . . . . . 6
scopes)Yoshinori Yonekura
Status report of the Tsukuba VLBI Station – damage of the antenna basement . . . . . . 8
due to overloading –Takahiro Wakasugi
Development of Wide-band VLBI system (Gala-V)
Mamoru Sekido, Kazuhiro Takefuji, Hideki Ujihara, Thomas Hobiger,
Masanori Tsutsumi, Shingo Hasegawa, Yuka Miyauchi, Ryuichi Ichikawa,
Yasuhiro Koyama, and Tetsuro Kondo. . . . . 11

A status of the First Black Hole Imager, CARAVAN-SUBMM at 2012
Makoto Miyoshi, M. Sekido, Y. Koyama, H. Ujihara, Y. Irimajiri, H. Ishitsuka,
S. Nemoto, Y. Asaki, M. Tsuboi, T. Kasuga, S. Nanbu, A. Tomimatsu, M. Takahashi, H. Saida, S. Machiya, Y. Eriguchi, S. I. Yoshida, S. Koide, R. Takahashi, T. Oka, J. Furusawa, N. Kawaguchi, Y. Kato, K. Niinuma, T. Daishido,
K. Wakamatsu, T. Terasawa, M. Teshima, T. Kakimoto, Y. Tunesada. . . . . 15

(continued on inside front cover)Flux monitoring observations of Sgr A∗ at S/X bands with the NICT . . . . . 18
Kashima–Koganei VLBI System
Shunya Takekawa, Tomoharu Oka, and Mamoru Sekido
The Study of Time Synchronization over VPN. . . . . 21

Yusuke Kito and Fujinobu Takahashi
Toward a Precise Frequency Comparison with VLBI TechniqueKazuhiro Takefuji, Mamoru Sekido, Hideki Ujihara, Thomas Hobiger,
Masanori Tsutsumi, Shingo Hasegawa, Yuka Miyauchi, Ryuichi Ichikawa,
Yasuhiro Koyama, and Tetsuro Kondo. . . . . 25

Combination of space geodetic techniques on the observation level with c5++ . . . . . 29
Thomas Hobiger and Toshimichi Otsubo
New Project for Constructing a VLBI2010 Antenna in Japan
Yoshihiro Fukuzaki, Tadashi Tanabe, Jiro Kuroda, Shinobu Kurihara,
Ryoji Kawabata, and Takahiro Wakasugi. . . . . 33

VLBI2010 – Newly Established VLBI Station –. . . . . 37

Shinobu Kurihara
Developments of K3, K4, and K5 VLBI Systems and Considerations for the . . . . . 39
new K6 VLBI System
Yasuhiro Koyama
Development of the Software Polarization Spectrometer “PolariS”
Izumi Mizuno, Seiji Kameno, Makoto Kuro, Amane Kano, Fumitaka Nakamura,
Noriyuki Kawaguchi, Yoshiaki Hagiwara, Katsunori Shibata, Nario Kuno,
Ryohei Kawabe, Shuro Takano, Daisuke Iono, and Seisuke Kuji

. . . . . 44

- News - News - News - News Restoration of 34m Antenna Azimuthal Wheel/Rail from the Damage of the . . . . 48
Earthquake 2011

September 2013

1

A Plan of the Automatic We have operated the telescope for 1,500 to 4,000
per year, mainly for surveys of NH3 molecObservation System for the hours
ular lines or monitors of H2 O maser toward theTomakomai 11-m Radio Tele- Galactic star-forming regions in a single-dish mode,
while for zero to 150 hours per year for VLBI obscope
servations.
One of the main observations using this telescope is a survey of dense molecular gas from whichstars form in inversion transition lines of NH3
molecule[1] , in order to clarify whether distribution
and physical properties such as temperature, density or star formation eﬃciency of dense molecular
gas is diﬀerent from one cloud to another. A recent
NH3 observation has revealed that dense molecular
gas exists in the star-forming region G23.44-0.18
Department Physics / Department oflocated near the end of the Galactic bar[2] . Two
Cosmosciences, Hokkaido University
Kita 10, Nishi 8, Kita-ku, Sapporo, 060-0810
molecular clouds[3] seem to collide each other inthis region, and the dense molecular gas is found
Abstract: The Tomakomai 11-m radio telescope has just in the overlap region. An additional obserbeen operated in 22-GHz band remotely from Sap- vation of H13 CO line in higher spatial resolution
poro about 70 km far away since the end of 2005. and higher sensitivity with the Nobeyama 45-m raThe telescope has been used for 1,500 to 4,000 dio telescope has suggested that the dense molechours per year, mainly for surveys of NH3 molec- ular gas formation was triggered by cloud-cloudular lines or monitors of H2 O maser toward the collision[2] .
Galactic star-forming regions. Automatic observation system for the telescope is planed to make ob- 2. Automatic Observation Systemservation more eﬃciently. We have started to modOur NH3 lines survey takes long time for inteify our programs for operating instruments and getgration
toward each observation position, since theting information on climate for preparation. Our
telescope
beam size of ∼ 4 is relatively larger than
plan of the new system is presented as well as the
typical apparent sizes of the regions emitting thepresent status of the telescope.
lines and thus beam dilution of the emission is severe. In order to ﬁnd a way out of the situation that
1. Present Statusman power for observation restricts our results of
The Hokkaido University Tomakomai 11-m ra- the survey, we have a plan to develop observation
dio telescope (Fig.1) is settled in Tomakomai about system for our telescope that make our survey more
70 km far away from Sapporo. The telescope was eﬃcient.
modiﬁed from geodetic VLBI system in S/X bands
The concept of our automatic observation systo VLBI/single-dish system in 22-GHz band and tem is as follows (Fig.2). An observer checks theoperated remotely from Sapporo since the end of whole system including the telescope and instru2005[1] .
ments once in a day and executing an observation
schedule ﬁle. Each schedule ﬁle consists of several observations, for example, the ﬁrst observation
targets the Orion region in NH3 lines, the second
one does the Taurus region in the same lines, thethird one monitors some H2 O masers, and so on.
The automatic observation system judges whether
weather condition is suitable for observation or not
and whether a target object is rising or not, when
the observation schedule is executed. The systemsets the instruments for each observation if the observation is possible to be done. Observation commands such as tracking a target, calculating the
Doppler frequency, starting integration, and so on,
are ordered at last. Status of the telescope andinstruments is reported from the system. In addiFigure 1. Tomakomai 11-m radio telescope.
tion, if some trouble has occurred, it is reported to
SORAI Kazuo (sorai@astro1.sci.hokudai.ac.jp),
MINAMIHARA Noriyuki,
MOTOGI Kazuhito, OHISHI Yukie,
HIURA Koichiro, UMEI Michiko,
SEGAWA Yoko, TASHIRO Takami,
SEKO Akifumi

IVS NICT-TDC News No.33

2

the observer through e-mail.

development for our automatic observation system
is making telescope controlling. We aim to test the
new telescope controlling system at the end of thenext March, however, developing the system may
take longer time.
4.

Acknowledgments

We acknowledge the Tomakomai Experimental
Forest, Field Science Center for Northern Biosphere, Hokkaido University and the members of
the Japanese VLBI Network. This project is ﬁnancially supported in part by the National Astronomical Observatory of Japan.
Figure 2. Schematic view of the concept of theautomatic observation system for the Tomakomai
telescope.
For developing the automatic observation system, we move the operating system from Windows
to Linux in order to make communication among
the computers which control several instruments
easier. We have just made a new IF (intermediate frequency) instruments controlling system in
Python and C on Ubuntu (Fig.3) and moved fromthe previous system in Agilent VEE Pro on Windows 2000. The new controlling system is very
functional and operation speed becomes higher
than the old system.

References[1] Sorai K., Habe A., Nishitani H., Hosaka K.,
Watanabe Y., Miwa S., Ohishi Y., Motogi K., Minamidani T., Awano J., Sumida S., Fukuya Y., Uchida R., Kaneko N., Fujimoto M. Y., Koyama Y., Kimura M., Nakai N.
(2008), Large-Scale NH3 Observations toward
the Galactic Star-Forming Regions I. W51
Molecular Cloud Complex, Publications of the
Astronomical Society of Japan, 60, 6, 1285–
1296, 2008[2] Ohishi Y., Sorai K., Habe A. (2012), Formation of Dense Gas and Stars near the End of
the Galactic Bar, Publications of the Astronomical Society of Japan, 64, 4, in press, 2012
[3] Rathborne J. M., Johnson A. M., Jackson J. M., Shah R. Y., Simon R. (2009),
The Astrophysical Journal Supplement, 182,
1, 131–141, 2009

Figure 3. GUI of our new IF instruments controlling system.
3.

Future Works

We make additional functions to the IF controlling system. Moreover, we have started making
a new monitor system for weather conditions andstatus of the instruments. These system will becompleted by the end of 2012. The most importantSeptember 20133

Hope on GHz-band width sig- maser lines for obtaining longer coherent exposure
In fact, this technique is being adopted in the
nal recording and 100 k-channel time.
Korean VLBI Network now in a commission phase
spectroscopy for VLBI imaging [6].
of astronomical maser sources
Hiroshi Imai (hiroimai@sci.kagoshima-u.jp)
Graduate School of Science and Engineering,Kagoshima University, 1-21-35 Korimoto,Kagoshima 890-0065, Japan
Abstract: High resolution and high dispersion spectroscopic imaging of astronomical maser sources
with VLBI technique is a powerful tool for study
on physical and dynamical structures of outﬂows
and accretion of interstellar matter seen around dying stars and young stellar objects. Simultaneous
mapping of multiple maser lines or some combination of maser line and continuum emission in VLBI
should lead to a promising future in VLBI astronomy. Overcoming of a trade-oﬀ between wide band
recording in VLBI backends and high dispersion
spectroscopy in a correlator has been a long-term
issue standing in front of such a future. Flexible
digital ﬁltering after high speed digital sampling aswell as multi base band channel capability and its
ﬂexibility in signal correlation should be key technology, but nowadays in a realistic level. Here I
show an example of possible future astronomical
application of such technology to study on siliconmonoxide (SiO) maser sources associated with circumstellar envelopes.
1.

Introduction

Simultaneous mapping observations of multiple
spectral lines such as SiO v = 3, v = 2, v = 1
J = 1 − 0 maser transitions at rest frequencies
of 42.5, 42.8, and 43.1 GHz, respectively, ammonia (NH3 ) and water vapor (H2 O) masers at 23.7
and 22.2 GHz, respectively, hydroxyl (OH) andmethanol (CH3 OH) masers at 6.0 and 6.7 GHz, respectively, and another OH maser and neutral hydrogen (HI) lines at 1.6 and 1.4 GHz, respectively
not only improve the eﬃciency of the observations
and their scientiﬁc outputs. They should provide
great opportunity to compare the observed parameters of these emission (absorption for HI and sometimes OH) lines such as spatial and line-of-sight velocity distributions and intensities and to explore
the physical and dynamical conditions of the target
objects. As an example, Figure 1 shows the importance of simultaneous observations of SiO maserlines mentioned above. Furthermore, they enable
to detect fainter maser lines by using the “phasereferencing technique” with the data of brighter

Figure 1. Energy level diagram of an SiO molecule.
Thermal and maser transitions observed in interstellar gas clouds and circumstellar envelopes arepresented by red lines. Solid and dashed arrows indicate the excitation of molecule through the “lineoverlapping” mechanism (e.g., [7]). This mechanism supposes that SiO molecules are excited byinfrared emission from water vapor molecule in thecircumstellar envelope. Note that the wavelengthof the IR emission corresponds to the diﬀerence inenergy levels between ro-vibrational states of SiO
and can pump the SiO molecule so as to have anenergy whose corresponding temperature is higher
than that on the stellar surface. Alternatively, collisional excitation by shocks transferred from thestellar surface through stellar pulsation is also expected. These two diﬀerent excitation mechanisms
predict diﬀerent performances of the diﬀerent SiO
maser lines at v =1, 2, and 3, e.g., spatial distributions and their temporal variations. They are
currently observed in VLBI at 43, 86, and 129 GHz
bands.
2.

Demonstration of simultaneous VLBI
observations of multiple SiO maser lines

We have demonstrated current capability of simultaneous VLBI observations of multiple maserlines using Japanese VLBI Network, in which four
VERA 20 m, the NRO 45 m, and the NICT 34
m telescopes have taken part in the observations.
One of such observations was reported in the paper[4]. Because a total band width is currently limited to 500 MHz in band pass ﬁltering after down

IVS NICT-TDC News No.33

4

conversion to the base band frequency, only twoof the three SiO maser lines mentioned above canbe simultaneously observed. Therefore, one pairof the maser lines are observed in one day, andother pair in the next day, eventually the total observation time is doubled. Due to incompatibilityof high speed recording systems between VERA(DIR2000) and other two telescopes (e.g., K5), low
speed recording system (DIR1000) should be usedin order to obtain higher sensitivity for maser line
observations with the NRO and NICT telescopes.
As a result, estimation accuracy of group delay
residuals is limited to ∼5 nsec due to too sparsemonitoring of the residuals with only a bright calibrator. This causes a phase gradient of ∼1.5 turnof phase rotation between the two maser lines separated by ∼300 MHz when one applies the phasereferencing technique using the data of brighter
maser lines to transfer their group delay solutions
to the data of fainter maser lines. Furthermore, because the SiO masers are highly variable, even on
a day scale, the position reference SiO v = 2 maser
spot observed in both of two pairs of maser lines isalso spatially unstable (σ ∼2 mas).
Figure 2 shows the obtained composite map of
SiO v =1, 2, and 3 J = 1−0 maser lines towards thesemiregular variable star W Hyrdae. Interestingly,
only the v = 3 line has spatial oﬀsets towards thecentral star with respect to other lines, suggesting
the collisional excitation of the v = 3 maser line.
However, when taking into account the relative position accuracy limited by the above-mentioned accuracy of estimated group delay residuals, these oﬀsets are still on the level of marginal identiﬁcation.
3.

Near future issues in wide-band spectroscopic VLBI observations

Thus, a high speed, wide bandwidth signal
recording system is desired to observe the threemaser lines at the same time. First of all, the bandwidth of the band pass ﬁlter in frequency down
conversion should be expanded to 1 GHz or larger.
The current baseband convertors as installed in
VERA reduces the total bandwidth to 500 MHz.
Because the upstream data of these down convertors have intermediate frequency (IF) signals at 5–
7 GHz, the high speed sampler currently under development and in coming commissioning (in e.g.,
ADS3000+ and the OCTAVE system (OCTAD),
Kawaguchi, N. in private communication) can beused for this down conversion and signal ﬁltering.
On the other hand, even if the high speed recording system is available, the spectral resolution is
insuﬃcient in the current correlation system suchas Mitaka FX correlator [1]. The requested total
bandwidth and spectral resolution for the case of

Figure 2. Comparison among the distributions of
the SiO v =1, 2, and 3 (J = 1 − 0) maser emission observed in W Hya on 2009 February 27–28
for 2 × 6 hours [4]. The ﬁgure shows composite
velocity-integrated maps of the SiO v =1, 2, and 3
masers. The contour levels are described at the bottom of the ﬁgure. The map origin is located at thev = 2 maser spot that was observed on February
28 and used as fringe-phase reference. A dashedline ellipse indicates a ring-shaped brightness morphology of the SiO v =1 and v =2 maser emission
roughly ﬁtted by eye. A orange circle indicates thesize of the ”radio photosphere” of the star [8].
SiO maser observations described above (750 MHz
and 16 kHz, respectively) exceed the speciﬁcationof current correlators (16 784 and 1 024 spectral
channels in Fourier transformation and correlation
output, respectively, for Mitaka FX correlator). It
is desired to obtain spectroscopic data from thewhole receiving bandwidth in the uniform spectral
resolution. However, the data analysis softwares
and the architectures of end users’ personal computers may not deal with a huge number of spectral channels, over 100 000 in the case of lower frequency band VLBI spectroscopy. In spite of absence of any spectral line in a speciﬁc frequency
range, low frequency resolution data from sucha frequency range is still necessary for detecting
continuum emission of the target source. Thus
the spectral resolution should be ﬂexibly changed
through the total bandwidth. Software correlation
systems as developed in NICT and Swinburne University of Technology (DiFX, e.g., [5, 2]) should bequite ﬂexible to these requirements.

September 2013
Taking into account the trade-oﬀ between thewider bandwidth and sharper spectral resolution
as discussed above, the technology of digital ﬁltering (e.g. [3]) is still essential. Today, the total
bandwidth in signal receivers and digital samplers
is much larger than that with which VLBI correlators can deal (in real-time processing speed).
The digital ﬁlter shall choose frequency ranges relatively essential for signal processing and transfer
the ﬁltered signals in moderate sampling rates tothe correlators.
For VLBI spectroscopy, balanced development ofreceivers, samplers, digital ﬁlters, recorders, andcorrelators is quite essential. From the author’s
point of view as an astronomer, the current development environment of VLBI in Japan looks
optimistically observable since starting the development of software correlation system [5]. The
replacement of VERA’s correlation system to asoftware correlator (Kimura, M. and Oyama, T.,in private communication) in 2013 will approach
the fruitful astronomical situation described above.
Data analysis scheme that can process the correlated data produced under such a situation is under construction by the author1 , including pipeline
processing scripts and maser spot ﬁnding algorithm.
4.

Acknowledgment

HI was ﬁnancially supported by Grant-in-Aid for
Scientiﬁc Research from Japan Society for Promotion Science (20540234).
References[1] Chikada, Y., Kawaguchi, N., Inoue, M., Morimoto, M., Kobayashi, H., & Mattori, S.,
The VSOP Correlator, Frontiers Science Series, Proceedings of the International VSOP
Symposium held at the Institute of Spaceand Astronautical Science on December 5–7, 1989 and Proceedings of the mm-Wave
VLBI Workshop held at the Nobeyama Radio Observatory on December 8–9, 1989,
Tokyo, Japan, eds. Hirabayashi, H., Inoue, M.,
Kobayashi, H., Nishiniura, H., Okumura, S.,
Kuji, S., Sato, K., Asar, K., Sasao, T., &Kiuchi, H. (Universal Academy Press), p.369(1991)[2] Deller, A., Tingay, S. J., Bailes, M., &West, C., DiFX: A Software Correlator for
Very Long Baseline Interferometry Using Multiprocessor Computing Environments, Publi1 see the wiki page of software repository of theJapan VLBI Consortium: http://milkyway.sci.kagoshimau.ac.jp/groups/vcon lib/wiki/9fbfd/Data Analysis.html .

5cations of the Astronomical Society of the Paciﬁc, 119, 318–336 (2007)[3] Iguchi, S., Kurayama, T., Kawaguchi, N., &Kawakami, K., Gigabit Digital Filter Bank:
Digital Backend Subsystem in the VERA
Data-Acquisition System, Publications of the
Astronomical Society of Japan, 57, 259–271(2005)[4] Imai, H., Nakashima, J., Deguchi, S., Yamauchi, A., Nakagawa, A., & Nakagawa, T.,Japanese VLBI Network Mapping of SiO v =3 J = 1−0 Maser Emission in W Hydrae, Publications of Astronomical Society of Japan, 62,
431–439 (2010)[5] Kondo, T., Kimura, M., Koyama, Y., &Osaki, H., Current Status of Software Correlators Developed at Kashima Space Research Center, International VLBI Service forGeodesy and Astrometry 2004 General Meeting Proceedings. Ottawa, Canada, eds. Vandenberg, N. R., & Baver, K. D., NASA/CP2004-212255, p.186 (2005)[6] Kim, H.-G., Han, S.-T., & Sohn, B. W., The
Korean VLBI Network Project, Exploring theCosmic Frontier: Astrophysical Instruments
for the 21st Century. ESO Astrophysics Symposia, ESO series, eds. Lobanov, A. P., Zensus, A. J., Cesarsky, C., & Diamond, P. J.,(Springer-Verlag, Berlin and Heidelberg, Germany), p.41 (2007)[7] Nakashima, J., & Deguchi, S., CORRELATION BETWEEN INFRARED COLORSAND INTENSITY RATIOS OF SiO MASERLINES, Astrophysical Journal, 669, 446–458(2007)[8] Reid, M. J., & Menten, K. M., IMAGING THE RADIO PHOTOSPHERES OFMIRA VARIABLES, Astrophysical Journal,
671, 2068–2073 (2007)

IVS NICT-TDC News No.33

6

Present Status of Ibaraki sta- can be used as a spectrometer system for single
observations.
tion (Takahagi and Hitachi 32- dishWe succeeded ﬁrst scientiﬁc VLBI imaging obserm Radio Telescopes)
vations at 6.7 GHz in Aug. 2010. We also achieved
Yoshinori YONEKURA(y.yone@mx.ibaraki.ac.jp)
Center for Astronomy, Ibaraki University
2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan
Abstract: We brieﬂy introduce the present statusof the Ibaraki station as of 2013.
1.

Introduction

Takahagi and Hitachi 32-m antennas, which havebeen used for satellite communications at 4 and
6 GHz by KDDI, were decommissioned in Mar.
2007. These antennas were handed over to NAOJ
in Jan. 2009, and now belong to the Ibaraki station,
which is a branch of Mizusawa VLBI Observatoryof NAOJ. NAOJ and Ibaraki University, in cooperation with ISAS/JAXA, NICT, GSI, and universities (Hokkaido U., U. Tsukuba, Gifu U., Osaka
Prefecture U., Yamaguchi U., and Kagoshima U.)
have decided to use these antennas for Japaneseand East-Asia VLBI network. We will use theseantennas for single dish and 2-element interferometric observations as well as VLBI.
2.

“ﬁrst fringe” in June 2012 between Takahagi and
Tsukuba at 22 GHz using K5/VSSP32. We also
succeeded test observations using wide-band (500
MHz BW) HDD recording system (K5) between
Hitachi and Tsukuba at 8 GHz in Nov. 2012.
We are now testing two-element array using Hitachi and Takahagi antennas.
3.

The system noise temperatures were measured
to be ∼25 K and ∼50 K for the C/X and K-band,
respectively, including atmosphere toward zenith.
The pointing accuracy is ∼0.3 arcmin, which ismeasured by the observations of strong radio continuum sources such as 3C273 at 8 GHz. The aperture eﬃciency at 6.7 and 8 GHz is measured to be
55–75% for Hitachi antenna, and 55–60% for Takahagi antenna. The aperture eﬃciency at 22 GHz is
measured to be ∼30% at 22 GHz for both antennas.
These performances are summarized in Table 2.
The location of the antennas are measured by using high-accuracy GPS measurement system (Table 3). These values are changed from the values[1]measured before “The 2011 oﬀ the Paciﬁc coast of
Tohoku earthquake”.

Renovation of Satellite-Communication 4.
Antennas into Radio Telescopes

The renovation of satellite-communication antennas into radio telescopes started from FY2009,and has been almost ﬁnished until FY2012 (Table 1).
The antennas themselves are not refurbished.
Feed horn is newly developed for the observations
at 6.7, 8, and 22 GHz. Antenna control system isnewly installed.
We have been developing two cooled receiver systems for each antenna. One is covering 6.5–8.8 GHz(C/X-band), for observations of 6.7 GHz methanol
masers and 8 GHz continuum. Two sets of C/Xband receivers have been completed. The other iscovering 21–25 GHz (K-band), for observations of
22 GHz H2 O masers and continuum. In addition,
K-band receiver is also used for single-dish observations of molecular lines as NH3 and CCS. One
set of K-band receiver have been completed, andthe second set will be available within FY2013.
As for the VLBI backend, magnetic-tape recording system (so-called VSOP terminal, K4), 5 sets of
K5/VSSP32 HDD recording system (32 MHz BW),and wide-band (500 MHz BW) HDD recording system (K5) are successfully installed. K5/VSSP32

Performances of Telescopes

Start of Scientiﬁc Observations using
Single-Dish and Short-Baseline VLBIAs mentioned above, VLBI scientiﬁc observations have started in 2010. We recently started
single-dish and short-baseline VLBI scientiﬁc observations. We have started single-dish observations to monitor the ﬂux of methanol masers at 6.7
GHz from Dec. 2012 using Hitachi antenna. About
400 masers are observed more than once per 9 days.
We also started daily short-baseline VLBI observations in order to monitor the ﬂux of Sgr A* at
22 GHz from Feb. 2013 using Takahagi antennaamong Mizusawa 10-m and Gifu 11-m antennas.
Acknowledgments
We acknowledge NICT for the use of correlation
software. This work was supported in part by JSPS
KAKENHI Grant No. 24340034.
References[1] Yonekura, Y., IVS NICT-TDC News No.32,
24–25, 2011.

September 2013

7

Table 1. Development status

Single dishantenna control software
6–9 GHz cooled Receiver
22 GHz cooled Receiverspectrometer (K5/VSSP32)
VLBI
with K4 recorderwith 500 MHz BW sampler+HDD
Two element arraycorrelator

HitachiTakahagi

2009 Nov.
2010 Aug.
(2013)
2012 Mar.

2012 Oct.
2010 Dec.
2012 Dec.
2012 Mar.

2010 Aug.
2012 Nov.

2013 Mar.
2013 Mar.

(2013)

Table 2. Antenna performances

Aperture Eﬃciency
Tsys * (@ El = 90◦ )Beam size ( )SEFD (Jy)

6.7 GHz
0.55–0.75
25–30
4.6
130–160

8 GHz
0.55–0.75
25–30
3.8
130–160

22 GHz∼0.3
50 (winter)–100 (May)
1.6
570–1150

Table 3. Antenna location (as of September 2012)
X (km)Y (km)Z (km)
Hitachi−3961.788796 +3243.597525 +3790.597709
Takahagi −3961.881647 +3243.372513 +3790.687466
Distance between 2 antennas: 259.438 (m)IVS NICT-TDC News No.33

8

Status report of the Tsukuba Table 1. Speciﬁcation sheet of the parabolic anVLBI Station – damage of the tenna of the Tsukuba VLBI Station
antenna basement due to overParameterValueloading –Height36m
Takahiro Wakasugi (t-wakasugi@gsi.go.jp)
Geospatial Information Authority of Japan
1 Kitasato, Tsukuba, Ibaraki 305-0811, Japan
Abstract: The Geospatial Information Authority ofJapan (GSI) has carried out a lot of VLBI experiments in the Tsukuba VLBI Station, which wascompleted in 1998. We carried out 87 times of 24hour session and 131 times of 1-hour session in lastyear. Thus, GSI has been contributing to the International VLBI Service for Geodesy and Astrometry (IVS). On the other hand, a lot of loads had
been applied in the substructure of the azimuth
rail. About ﬁve years ago, it was discovered thatthe phenomenon of the spurt of farinaceous matterfrom Grout of the antenna basement. It turned outthat the situation of the antenna was very serious.
In this paper, I report the state of the Tsukuba
VLBI Station and inform a possible trouble of thesubstructure of antennas that have the wheel &track structure.

Diameter
WeightSlew speed
Construction

32m
550t
3 deg/sec
1998

Figure 1. The number of annual experiments carried out in the Tsukuba VLBI Station after its completion in 1998. GSI has carried out approximately
200 times of VLBI experiments annually for the
past several years in the Tsukuba VLBI Station.

according to the results of the pointing oﬀset checkwith X band, it was emerged that the damage
The Tsukuba VLBI Station has a parabolic anwas getting worse rapidly from 2008, and it cortenna with 32-m diameter and slewing speed of an
responded to the beginning of the spurt of Grout.
unprecedented high mobility of 3 deg/sec in spite
The maximum azimuth oﬀset versus the azimuthof its weight of 550 tons (Table 1.). It has been
direction became about 0.06 degree (Figure 4) inplayed an important role of VLBI experiments in
the result of the pointing oﬀset check in April 2013.
eastern Asia after its construction in 1998 (Figure
The eﬀect of the oﬀset also appeared in the re1). However, the spurt of farinaceous matter fromsults of the correlation processing recently, and at
Grout was detected about ﬁve years ago and relast GSI had interrupted all experiments with thecently it seemed that the volume of the spurting
Tsukuba VLBI Station since May 2013.
matter increased acceleratingly.
Figure 2 shows the antenna substructure of the 2. Investigation of the Substructural DamTsukuba VLBI Station. The rail is mounted on theage of the Antenna
stiﬀ metallic plate, which is called sole plate, andWe contacted the manufacturer of the antenna
they are ﬁxed on the basement concrete by someanchor bolts. The gap between the sole plate and immediately to investigate the damage of the basethe basement concrete is fulﬁlled by Grout, which is ment. Two kinds of investigations were carried out;
composed of the material like cement. It is consid- ﬁrst was measurement of the amount of subsidence
ered that the frictional force due to the heavy usage of the sole plate against Grout by using dial gauges
made some parts of Grout farinaceous. Then, pen- while the wheel was passing on. It was carried out
etrated rain water weakened the strength of Grout at 117 points throughout the whole circumference.
furthermore, and ﬁnally farinaceous matter from Second was direct observation of the actual state
Grout spurted out when a load of the antenna was of the substructure by excavating Grout. Based on
the subsidence result the excavation of Grout wasapplied (Figure 3).
The inﬂuence of the damage appeared in the re- carried out at four points. Three points were losults obtained by some experiments. In addition, cated where large subsidence was measured includ1.

Introduction

September 20139

ing the maximum subsidence, and another point
was located where subsidence was never measured.
The results of the investigations will be explainedin the next paragraph.
3.

Results of the Investigations

The result of the ﬁrst investigation is shown in
Figure 5. There were 9 points with larger subsidence than 2-mm, and the maximum subsidence
was 3.5-mm. The amounts of gaps between thesole plate and Grout observed directly by excavating Grout corresponded to the results of subsidence
obtained with dial gauges (Figure 6). On the other
hand, the sole plate and Grout seemed to standclose each other at the excavated point where no
Figure 2. A schematic diagram of the antenna sub- subsidence was measured. These results impliedthat there were some gaps between the sole plate
structure of the Tsukuba VLBI Station.
and Grout at the points where subsidence was measured.
I compared the results of subsidence and thepointing oﬀset data with X band. When the antenna was oriented to the direction of the large
pointing oﬀset, three wheels were located on therail where subsidence was larger than 2-mm (Figure 7). Similarly, when the antenna was oriented
to another directions of the large pointing oﬀsets,most of wheels were located on the positions withlarge subsidence. These results indicate that the results of the pointing oﬀset check with X-band andsubsidence with dial gauges are matching qualitatively. That is, when some of the wheels locate on
the points with large subsidence, the subsidence ofantenna causes the pointing oﬀset. However, theFigure 3. Photograph of the antenna substructure
subsidence of the antenna of 3.5-mm brings aboutof the Tsukuba VLBI Station. Farinaceous Groutthe pointing oﬀset of about 0.01 degree, so thatspurted out from the gap between the sole plate andthe subsidence of 3.5-mm is not enough to explain
Grout.
the result of 0.06 degree maximum pointing oﬀset. This means that it is insuﬃcient for us to understand the actual state of the antenna basement
only by the measurement of subsidence with dialgauges. Considering the amounts of gaps between
the sole plate and Grout, there is a possibility thatthe rail and sole plate already subside due to theirown weight although they doesn’t take a load of
the antenna.
4.

Figure 4. Result of the azimuth pointing oﬀset
check with X band versus the azimuth direction
measured in April 2013. The maximum oﬀset isapproximately 0.06 degree.

Countermeasure and Future PlanAs I have just mentioned, the investigation of
measurement of subsidence of the sole plate against
Grout is not enough for us to know the actual stateof the antenna substructure. Therefore we plan
more investigation of the state of the antenna bymeasuring the level on the rail surface. After theinvestigation is ﬁnished, we intend to repair it withthe best method derived from the results of all investigations. As one of the countermeasures, weIVS NICT-TDC News No.33

10

Figure 5. The results of the measured movementsof the sole plate against Grout with dial gauges.
The upper polygonal line indicates the amount ofrise and the lower one shows the amount of subsidence of the sole plate against Grout. The measurement was carried out at 117 points throughout
the whole circumference.

Figure 7. The locations of wheels when the antenna
is oriented to the direction of the large pointing oﬀset. The arrow signiﬁes the direction of the antenna and wheels locate on four dotted lines. Three
wheels correspond to the points where subsidence ofthe sole plate against Grout is large.
plan to inject new Grout of resinous material withkeeping rail surface horizontal position. Finally, we
aim to repair all damage and resume VLBI experiments as soon as possible.
5.

Summary

It was emerged that the damage of the substructure of the Tsukuba VLBI Station was very serious. Because it had a bad inﬂuence on some experiments, we decided to cancel all experiments in the
Tsukuba VLBI Station after May 2013. The resultsof the investigations showed that there were some
gaps between the sole plate and damaged Grout,and the maximum subsidence was 3.5-mm. We
plan to investigate the damage in more detail andaim to resume experiments after repairment of theantenna basement.

Figure 6. Photograph of the state of the antenna
substructure after excavating Grout. The gap of afew millimeters was detected between the sole plate
and Grout.

September 201311

Development of Wide-band
VLBI system (Gala-V)
Mamoru Sekido (sekido@nict.go.jp),
Kazuhiro Takefuji, Hideki Ujihara,
Thomas Hobiger, Masanori Tsutsumi,
Shingo Hasegawa, Yuka Miyauchi,
Ryuichi Ichikawa, Yasuhiro Koyama, andTetsuro Kondo
Space-Time Standards Laboratory, Kashima SpaceTechnology Center, NICT893-1 Hirai, Kashima Ibaraki, Japan

1.

Introduction

Based on the needs of precise frequency comparison between atomic frequency standards at intercontinental distances, project of VLBI application
for frequency comparison has started [1]. Takiguchi
et al.[2] have made an experiment for comparison
between VLBI and other frequency transfer techniques, such as Two-Way Satellite Time and Frequency Transfer (TWSTFT), GPS, and a special
equipment (TCE) on Japanese Engineering satellite ETS8. They conﬁrmed that VLBI has a potential of frequency comparison between distantatomic standards. Figure 1 shows results of another inter-comparison experiment between GPS
common view, TWSTFT(Code phase), and VLBI.
The data of VLBI measurements in the ﬁgureshows sum of estimated clock model polynomials
and post ﬁt residuals from CALC/SOLVE output.
This experiment demonstrated that the precisionof the measurement could be improved by increaseof eﬀective bandwidth of VLBI observation.
In the next step, we proceeded to develop a VLBI
system with wide-band observation capability,
which is semi-compliant with VGOS (VLBI2010
Global Observing System) speciﬁcation. Transportable compact antennas are practically necessary to compare optical frequency standards in laboratories at distant location. For compensating disadvantages of small collecting area of the compact
antennas, wide-band observation frequency range
and combination with large diameter antenna areused for boosting the signal to noise ratio (SNR)
of VLBI observations. Our wide-band observation system named ‘Gala-V’ employed a ﬁxed frequency allocation in the frequency 3-14 GHz range,

0.8
0.6
0.4
Time difference(nsec)

Abstract: The project mission of our group is realization of compact VLBI system for precise frequency comparison between distant atomic frequency standards. For this mission, development of
a new wide-band VLBI observation system named‘Gala-V’ is in progress.

GPS Common view, Carrier Phase
Two Way Satellite, Code Phase
VLBI-1, Polynomial+Residual
VLBI-1, Estimated Polynomial(30min.)
VLBI-2, Polynomial+Residual
VLBI-2, Estimated Polynomial(30min.)

VLBI:without cl-rate constraint

0.2
0
-0.2
-0.4
-0.6
-0.8
-1
-1.2
55976

55976.5

55977

55977.5

55978
MJD

55978.5

55979

55979.5

55980

Figure 1. Experiment results of inter comparison of
frequency transfer techniques (GPS Common View,
TWSTFT Code, and VLBI). The experiment was
conducted in Feb. 2012 between Kashima and Koganei 100 km distance. VLBI-1 and VLBI-2 are
the continuous experiments with diﬀerent frequency
arrays. Eight X-band channels are spread over 500
MHz bandwidth in VLBI-1(‘*’), and the same number of channels are allocated in 1 GHz bandwidth in
VLBI-2(‘2’). Data sampling mode was 32Msps1bit-16ch for both of two VLBI experiments. The
result indicating that Weighted Root-Mean-Square(WRMS) of the residual were improved in case ofwider bandwidth (VLBI-2) than the narrower case
(VLBI-1).
whereas the VGOS requires ﬂexible frequency selection capability in the 2-14 GHz range.
2.

RFI survey and Frequency Array

One of the reason of ﬁxed frequency arrangement
is due to technical restriction in designing wideband feed system for 34m radio telescope, which is
modiﬁed Cassegrain type. Full width of the viewing angle from the secondary focal point to the subreﬂector is 35 degrees, whereas popular wide band
feed such as the Quad-Ridge Flared Horn (QRFH)
has 60-120 degrees of beam width. Since newly de-IVS NICT-TDC News No.33

12

Table 1. Gala-V system parameters
Diameter of Antennas
34m, 1.6m, 1.5m
3500 - 4524 MHz
Observation
5100 - 6124 MHz
Frequency
9900-10924 MHz
13100-14124 MHz
Band width/Channel
1024 MHz
System Temperature
150-200 K
Eﬀective Bandwidth
3.8GHzTarget Delay Precision
10 psec.
signing of a feed with narrow constant beam width
over the wide frequency range will need long term
research work, thus we decided to reduce the requirement condition of the VGOS speciﬁcation for
quickly realizing the multi-band observation system.
The frequency allocation was determined basedon RFI (Radio Frequency Interference) survey, feed
design condition, and consideration on delay resolution function. The RFI surveys were performedat Tokyo, Kashima, and Tsukuba. Figure 2 shows
the results of survey made by max-hold method
for 30 sec. in four horizontal directions (North,East, South and West). Since RFI was strong at
lower frequency below 3 GHz, the survey was madeby eliminating the signal at lower frequency withhigh pass ﬁlter (Fc=3.5GHz). Selected observation
frequencies are indicated with rectangular boxes
in Figure 2. Several RFI signals are still remaining in the observation bands, and they are to be
suppressed by additional analog ﬁlters. Table 1
shows the current Gala-V system parameters. In
the process to select the frequency of observation
bands, feasibility of designing the multi-band feed
was took into account. A prototype of the newmulti-band feed is under development now, and it
will be installed on the Kashima 34m antenna inthis year. It is notable that frequency intervals of
this array have a property of integer number of ratio 1:3:2 with multiple of 1.6 GHz. This is based on
no-redundancy array theory[3], which enables ﬁnedelay resolution with minimum side-lobes. Good
points in using ﬁxed frequency array strategy areenabling quick development of the wideband VLBI
system and quick catch up utilizing broadband delay observable. Its disadvantages are potential risk
to be suﬀered from RFI, and limited compatibility
in participating with VGOS observations.

Table 2. Typical Parameters of K6/OCTAD-G(‘GALAS’) Sampler.
Sampling rate
16384 MHz
Typical output rate of sam4096 Msps
ples per port
Sampling quantization
3 bit
Output Quantization
1 or 2 bit
Number of output
4 ports
10Gbit Ethernet
Output interface
10GBASE-SR
Number of analog inputs
2
Max. input radio Frequency
16.4 GHz
NAOJ, has the digital baseband conversion function. Two IF inputs with 1 GHz bandwidth signal are sampled at 2048 MHz at maximum, andfollowing FPGA circuit works as digital ﬁlter for
extracting arbitrary 16 × 32 MHz signals. The
data stream of 2 × 2048 Mbps are recorded in each
two PCs equipped with VSI-H interface card ‘PCVSI’. Therefore using four sets of ADS3000+ enables basic VGOS compatible observation, in which
16 channels of 32MHz band width are captured in
the each band[4].
Besides this VGOS compatible observationmode, a challenge of using RF (radio frequency) direct sampling technique is going to be tested in thisdevelopment. Based on the success of the RF direct
sampling experiment performed in 2011[5], a new
sampler K6/OCTAD-G (code name ’GALAS’) is
under development. The K6/OCTAD-G has capability to sample the radio frequency signal at 16.384
GHz, then 4 × 1024 MHz signals are extracted
by digital ﬁlter function. Each four data output
stream comes out from four 10G-Ether ports separately in the VDIF data format in the UDP packet,
or VDIF data with the header of VDIF Transport
Protocol (VTP) over UDP. Thus any four RF signals with 1024 MHz bandwidth are captured from
16.4 GHz RF range simultaneously without analog
frequency conversion. 2.
4.

Compact Antennas and the last RHCP
X-band VLBI Experiment

The compact transportable antennas developed
by Ishii et al.[6] in the former project ‘MARBLE’
was equipped with the conventional S/X RHCP
geodetic receivers, although they have been originally designed with the wideband observation sys3. Data acquisition and a RF Direct Sam- tem of ‘VLBI2010’ in mind. Wideband QuadRidge Horn antenna has been used at the feedpler
system of the MARBLE. Therefore upgrading the
The ADS3000+ sampler, which was developed MARBLE antennas by expanding the observation
under the collaboration among NICT, JAXA, and frequency region is the shorter way to realize Gala-September 2013

13

Figure 2. RFI survey (H-linear polarization, Horizontal 4 direction, Max-hold 30sec.) results for
Kashima,Koganei(Tokyo) and Tsukuba. The measurements were made by using wide band receiver system with connecting high pass ﬁlter (Fc=3.5GHz) in front of the LNA. Four observation bands selected
for Gala-V system are indicated by rectangular boxes.

IVS NICT-TDC News No.33

14

Table 3. The result of X-band geodetic VLBI observation in Feb. 2013. Stations are MBL1:MARBLE
1.6m at Kashima, MBL2: MARBLE 1.5m at Koganei, Kas11: Kashima 11m, Kog11: Koganei
11m, Tskb32.
Post ﬁt
Residuals.
X-station:
Tskb32

Coordinates[mm]

SEFD Ratio
w.r.t.
Kas11

Kas11
Kog11
MBL1
MBL2
X:
MBL1 Y:Z:X:
MBL2 Y:
Z:
Kog11
MBL1
MBL2

25 psec
24 psec
28 psec
26 psec-3997598292±3
3276714203±33724293100±3-3942062635±3
3368276235±33702003846±3
2
200
300

V project. By the end of the second quarter of2013, low noise ampliﬁer (LNA) was replaced andcircular polarization was changed to linear polarization to expand the observation frequency range.
Signal down-link from the antenna to the observation room was also replaced from coaxial IF cable
to wideband and optical RF transmission system’E18000’ developed by Sumitomo Osaka Cement
Co. Ltd, which has ﬂat characteristic over wide
frequency range (1 – 18 GHz), low noise ﬁgure (NF≤ 5 dB), and positive gain (G ≥ 30 dB).
Before these modiﬁcations, the last geodetic
VLBI observation with the two MARBLE antennas was conducted in February 2013 together with
11m diameter antennas at Kashima and Koganei,
and 32m antenna of Geographical Survey Institute(GSI). The aim of this experiment was two folds.
One is to determine the terrestrial coordinates ofthe MARBLE antennas after the big earthquake of
2011. The second is to record the receiver performance before the upgrading for the Gala-V. S-band
was not used in this experiment because of strong
RFI coming into MARBLE antennas, which if vulnerable to RFI due to wider beam width. Thus
ionospheric delay correction procedure was not applied, however its delay contributions were supposed to be negligible because of relatively shortbaselines. Table 3 shows the station coordinatesand SEFD (System equivalent ﬂux density) ratioswith respect to that of Kashima 11m antenna estimated from the experiment data. Nominal SEFD
of Kas11 is 5500 Jy.

5.

Summary

Development of wideband VLBI system, which issemi-compliant with VGOS system, is in progressby upgrading the MARBLE system. The system
is supposed to work in combination with wideband small diameter antennas and middle class antenna. Target of delay measurement precision withthis system is at 10 pico seconds, and the keys toachieve this target are the wide eﬀective bandwidthand boosting of SNR by joint observation withlarger diameter stations. For quick catching up of
the development, we have chosen four ﬁx frequency
bands for this project. Development of wideband
multi-frequency feed for the Kashima-34m and RF
direct sampling technique are the new challengesof the technology.
References[1] Takiguchi, H., et al., Comparison with GPS
Time Transfer and VLBI Time Transfer,IVS
NICT-TDC News, No.28, 10-15, 2007
[2] Hiroshi Takiguchi, et al., Inter-comparison
Study of Time and Frequency Transfer between VLBI and Other Techniques (GPS,ETS8(TCE), TW(DPN) and DMTD), IVS
NICT-TDC News No. 32, 32–37, 2011.
[3] Moﬀet, A. T. , Minimum-Redundancy Linear
Arrays, IEEE, Trans. Ant.&Prop., Vol.AP16,No.2,pp172-185,1968.
[4] Chester Ruszczyk et al., VLBI2010 using the
RDBE and Mark 5C, IVS 2012 General Meeting Proceedings, .81–85, 2012.
[5] T.Kondo, Success in an X-band VLBI using
an RF direct sampling technique, IVS NICTTDC News No. 32, 51, 2011.
[6] Atsutoshi Ishii, et al., Current status of development of a transportable and compact VLBI
system by NICT and GSI, IVS NICT-TDC
News No. 31, 2–5, 2010.

September 201315

A status of the First Black Hole 2. Image Simulations
Imager, CARAVAN-SUBMM In order to image black hole horizon clearly,
Miyoshi et al. 2004, 2007 have showed importanceat 2012of shorter baselines around 1000 ∼ 2000 km at
Makoto Miyoshi(NAOJ,makoto.miyoshi@nao.ac.jp),
M. Sekido, Y. Koyama, H. Ujihara,
Y. Irimajiri (NICT), H. Ishitsuka,
S. Nemoto (IGP), Y. Asaki, M. Tsuboi(ISAS), T. Kasuga (Hosei Univ.),
S. Nanbu, A. Tomimatsu (Nagoya Univ.),
M. Takahashi (Aichi Univ. Edu.), H. Saida,
S. Machiya (Daido Univ.) Y. Eriguchi,
S. I. Yoshida (Tokyo Univ.), S. Koide(Kumamoto Univ.), R. Takahashi(Tomakomai), T. Oka, J. Furusawa (KeioUniv.), N. Kawaguchi, Y. Kato (NAOJ)
K. Niinuma (Yamaguchi Univ.),
T. Daishido (Waseda Univ), K. Wakamatsu(Gifu Univ.) , T. Terasawa, M. Teshima(ICRR), T. Kakimoto, Y. Tunesada(TITEC)
National Astronomical Observatory, Japan,
2-21-1, Osawa, Mitaka, Tokyo, Japan 181-8588
Abstract: We here report the present investigations
for the CARAVAN-SUBMM project.
1.

Introduction

CARAVAN-SUBMM is a project constructing
a sub-millimeter wavelength (submm) VLBI network at Andes for imaging and detecting black holehorizon and the surroundings that was never obtained before by any telescopes. It contains at least
two ﬁxed VLBI stations and one mobile VLBI station. “Mobile VLBI station” is a famous method
in Japanese geodetic VLBI experiments since midin the 1980s (Ichikawa et al., 2009). We apply
the method in order to cover the u-v plain eﬀectively and attain higher quality images at submm
VLBI than those only ﬁxed stations can do. By
observing SgrA*, a super massive black hole atour galactic center, we aim imaging observationsof the surroundings of the black hole horizon, andpave the way for veriﬁcation of the general relativity and open observational black hole astrophysics (Miyoshi et al., 2011). Collaboration with
the international ALMA increases the sensitivity
and number of detectable sources. CARAVANSUBMM with world collaboration can realize thehigher spatial resolution as well as 10 micro arc
second order that ALMA alone never achieves. We
report here the status of the project, CARAVANSUBMM at 2012.

230GHz. We performed further imaging simulations with changing model images and declinationsof the target source. As the results we found following points:
1. It is quite diﬃcult to resolve the true image
using only the EHT conﬁguration due to thelack of shorter baselines.
2. The diﬃculty still remains even if adding
phased ALMA to the EHT array.
3. It is also diﬃcult to obtain the disk shapearound BH as a synthesized image using only
CARAVAN-SUBMM array.
4. This diﬃculty still remains even if adding
phased ALMA to the CARAVAN-SUBMM array.
5. It is possible to resolve the true image under the collaboration with the EHT and the
CARAVAN-SUBMM.
6. Participating the phased ALMA to the above
two-combined arrays will not dramatically enhance the image quality.
These results follow the common sense that image
quality depends on how u-v plain can be covered.
To resolve the true image around black hole horizon, we need not only longer baselines corresponding to the earth diameter but also shorter baselinearound 1000 ∼ 2000 km at 230GHz. The essential role of phased-ALMA as a VLBI station is not
the ﬁrst detecting and imaging black hole horizon
with VLBI but to increase the number of detectablesources with millimeter to sub millimeter VLBI.
3.

Cost Down Study for Antenna

In order to realize the cost-down in making ahigh precision antenna panel for receiving millimeter to sub-millimeter wavelength, we examined theaccuracy of the surface of antennas made by metal
spinning method. Using an existing mold we could
attain a surface accuracy as well as 60μm r.m.s.
easily. As the results, we found that the surface
accuracy depends mainly on the accuracy of themold surface. If we can use a higher precision moldin metal spinning, the more accurate the antennasurface will be obtained. The surface accuracy willreach as well as r.m.s. 30μm level if we use sucha ﬁne mold. The surface accuracy of the metal
spinning antenna maintained within the 2 years of

IVS NICT-TDC News No.33

16

our research period. Because the metal spinningantenna is very thin, the surface can be deformed
easily by adding force non-uniformly. In practicaluse, a supporting structure of the antenna surface
is very important to maintain the high accuracy ofthe surface.

Figure 2. Mobile Station

Figure 1. Surface accuracy measurement of a 90
cm antenna made by metal spinning method.

4.

Mobile Station

Using several of very light antennas like those bymetal spinning method, we can make a very lightweighted radio telescope. As for telescope mount,a Japanese astronomer has already developed very
light and low cost system(Kurita et al. 2004, 2009).
Combining these we can make a radio telescope
suitable for transportation along Andes mountains
where road way is quite fully equipped today. The
Caravan will contain not one but at least three oftrucks. One for antenna carry, another for mountcarry, and the other is for electric power-supply andrecording electronics and hydrogen maser though
we suppose power supply at operating telescope iscommercial one. Among Peruvian Andes there aremany cities and towns. Commercial based electric
power supply is easily obtained.

Figure 3. Recent Survey Area

servatories have a long-period collaboration withJapanese researchers. Including the two observatories, we performed site survey both in Peru and
Bolivia for measuring the precipitable water vapor
amounts. We used an infrared water vapor meter(Takato et al. in preparation) that is very smalland easy to deal with. It has been used for surveying atmosphere in Antarctica, Tibet, and Atacama before. From 12th to 26th June in 2012, two
persons attended to the survey from Japan, joined
the IGP team, and performed the survey. They
investigated two areas. One is an area along theroad from Lima to Huancayo city including Huancayo observatory and COSMOS observatory (oldsolar observatory constructed by M. Ishituka). The
other area is along the road from La Paz in Bolivia through southern side of lake Titicaca to city
5. Observing Site Survey
Tacna in Peru. Tentative PWV values are about
We plan to construct the ﬁxed stations at around 10 mm at Huancayo (Peru, 3314m), about 4 mm
Huancayo Observatory (3300 m in altitude), IGP at Cosmos(Peru, 4600m) about 1.5 mm at Chacalin Peru and at the Chacaltaya Cosmic Ray Obser- taya(Bolivia, 5300m) and about 1.2 mm at southvatory (5300 m in altitude) in Bolivia. Both ob- ern desert area (Peru, 4600m). Chacaltaya and theSeptember 2013

17

Figure 4. Imaging simulation. EHT observation( Longer Baselinesj alone fails to ﬁnd intrinsic shape ofthe model image, though a false-shadow can be obtained. A better image can be obtained with Japanese
CARAVAN-SUBMM. Phased-ALMA has little contribution to the shadow image detection.
southern Peru area show excellently low PWVs aswell as those at ALMA site. Next step we plan toperform all season monitor at the two observatories. Also Huascaran, a north area of Peru must be
surveyed.
References[1] Miyoshi, M. et al., A First Black Hole Imager,
Caravan-sub at Andes, 2011ASPC,4 39, 279M
(2011)[2] Ichikawa, R., A. et al., IVS NICT-TDC News
No.30, (2009)[3] Miyoshi, M. et al., PTPS, 155,186-189, (2004).
[4] Miyoshi, M. et al., PNAOJ, 10, 15-23, (2007),or astro-ph/0809.3548[5] Kurita, et al.,”Ultra-Lightweight Telescope
Mount”, PASP, Vol. 121, Issue 877, pp.266271(2009)[6] Kurita, et al., ”Development of the ultralight
medium-size telescope”, 2004, SPIE, Volume5495, pp. 518-525(2004)

IVS NICT-TDC News No.33

18

Flux monitoring observations far brighter (∼ 1039 erg s−1 ) than now about several hundred years ago[1]. It is possible that AGN
of Sgr A∗ at S/X bands with the activities
are transient in general and currently inNICT Kashima–Koganei VLBI active Sgr A∗ may be active sometimes. Such variations may be caused by intermittent accretion of
Systeminterstellar gas onto the central SMBH.
Recently, the Max-Plank-Institute für extraterShunya Takekawa1 (shunya@z2.keio.jp),
restrische Physik (MPE) group has reported theTomoharu Oka1 , Mamoru Sekido2
discovery of a dense gas cloud, G2, which is on
its way toward Sgr A∗[2] (Figure 1). This cloud’s
1
Department of Physics, Faculty of Science andmass is approximately three times as the mass ofTechnology, Keio University
the Earth. The G2 cloud is on the elliptical or3-14-1 Hiyoshi, Kohoku-ku, Yokohama,
bit with high eccentricity (Figure 2) and thought
Kanagawa, Japanto reach the pericenter, ∼ 2000 Schwarzschild radii
2
Space-Time Standards Laboratory, Kashimafrom the nucleus, in Spring 2014[3]. The G2 cloudSpace Technology Center, National Institute ofhas been stretched and will be disrupted by the
Information and Communications Technology
strong tidal force from the central SMBH. Some893-1 Hirai, Kashima, Ibaraki, Japanfraction of disrupted cloud will infall toward the∗
Abstract: A compact radio source Sgr A is the nu- nucleus, increasing the mass accretion rate on tocleus of our Milky Way Galaxy, harboring a super- the SMBH. This increase in the mass accretion ratemassive black hole with mass of 4 × 106 M . While is expected to cause a signiﬁcant ﬂare in all wavethe current activity of our Galactic nucleus is ex- lengths. This G2 event provides a unique opportutremely low, an activation subsequent to the infall nity to witness a gas infall toward a SMBH. Thus,of the G2 cloud is expected within several years. In a number of groups are conducting and planning[4]
order to catch the ﬂux variations associated with to observe this event in every wavelength .
the G2 event, we have conducted ﬂux monitoring
observations of Sgr A∗ at S-band (2 GHz) and Xband (8 GHz) using the NICT Kashima-Koganei
VLBI system since the middle of February 2013.
We observed Sgr A∗ for 38 days in total, about ﬁvehours each day. Four quasars are also observed
as ﬂux calibrators. The X-band ﬂux density was
0.48±0.05 Jy (preliminary), while S-band emission
has not been detected. No signiﬁcant change nor
variation has been detected in the X-band ﬂux density of Sgr A∗ yet. We intend to continue thesemonitorings as often as possible until at least May
2014.
1.

Introduction

Most galaxies have supermassive black holes(SMBHs) at their centers, and some of them areobserved as active galactic nuclei (AGNs). Our
Galaxy also has a 4 × 106 M SMBH at its center, which is recognized as a compact radio source
Sgr A∗ . Despite its huge mass, Sgr A∗ is extremely
dim and quiet. The bolometric luminosity of thenucleus is only ∼ 1033−35 erg s−1 , which is far below the Eddington luminosity of 6 × 1044 erg s−1 .
This extreme dimness suggests a very low massaccretion rate (< 10−5 M yr−1 ), and thereby alow radiation eﬃciency. On the other hand, thewidespread (∼ 200 pc) distribution of Fe 6.4 keV
ﬂuorescent line emission implies that Sgr A∗ was

Figure 1. The infrared image of the central 1” ofthe Galaxy, taken by the MPE group[2] . Color show
the Br-γ images of the G2 cloud of four diﬀerent
epochs (red: 2004.5, green: 2008.3, blue: 2011.3)
overlaid on the Ks -band image at 2011.3.
2.

Observations

In order to catch the radio ﬂux variations associated with the G2 event, we have conducted ﬂux
monitoring observations of Sgr A∗ using the NICT
Kashima-Koganei VLBI system since the middle ofFebruary 2013. This VLBI system consists of two

September 201311-m diameter antennas located at Kashima andKoganei, and K5/VSSP32 samplers. Locations ofthese antennas are shown in Figure 3. The baseline
length is 109.1 km. Observing frequencies are Sband (2.21–2.29 GHz) and X-band (8.2–8.5 GHz).
Thus, the spatial resolutions of this VLBI systemare  280 mas and  70 mas at S and X bands,
respectively.
In radio range longer than mm-wave, it is known
that the apparent size of Sgr A∗ is roughly proportional to the square of observing wavelength, i.e.
Δθmas ∼ λ2cm . This behavior is explained by theelectron scattering in the line of sight[5] . Becauseof this, short (∼ 100 km) baseline is suﬃcient forthe cm-wavelength VLBI observations of Sgr A∗ .
Until 16 August 2013, we observed Sgr A∗ for
38 days in total, about ﬁve hours (EL > 15◦ ) eachday. Since 78th day-of-year (DOY), four quasars(NRAO 530, PKS 1622−253, PKS 1622−297, PKS
1921−293) are observed as ﬂux calibrators, while
only NRAO 530 had been used before 78th DOY.
The integration times are, 300s, 30s, 240s, 240s,
and 30s, for Sgr A∗ , NRAO 530, PKS 1622−253,
PKS 1622−297 and PKS 1921−293, respectively,in each observing sequence. All the source wereobserved by turns.
3.

Figure 3. NICT Kashima-Koganei VLBI system.
ﬂux of 3.3 Jy, we obtained the Sgr A∗ ﬂux by,
SSgrA∗ = 3.3 Jy × ρSgrA∗ /ρNRAO530 ,(1)

where ρSgrA∗ and ρNRAO530 are the correlation amplitudes averaged over each observing day. Fluxesof the other calibrators were calculated in the sameway. Note that quasars are variable in every wavelength, thus the ﬂux calibration method employed
here is a bit controversial. Nevertheless, the Xband ﬂux of Sgr A∗ is really stable, exhibiting no
signiﬁcant ﬂare or variation. We obtained the average X-band ﬂux is 0.48±0.05 Jy as a preliminary
value.
0.01
Sgr A*NRAO 530
1622-253
1622-297
1921-293

Correlation amplitude

Figure 2. The orbit of the G2 cloud determined by
the MPE group[2] . The small black star indicatesthe position of Sgr A∗ . Red points show observed
position of the G2 and red dotted line is its orbit.
Blue line shows the orbit of the S2 star, of which
the pericenter has been the nearest to the nucleus.

19

0.001

0.0001

1e-05
40

60

80

100

120

140
Day of year

160

180

200

220

240

Figure 4.
Correlation amplitudes of observed
sources at X-band. These amplitudes are values
averaged over each observing day. Error bars represent 1σ standard deviation for each day.

Results

Figure 4 shows a plot of observed correlation am- 4. Summary
plitude of Sgr A∗ at X-band. No signiﬁcant emisIn order to catch radio ﬂux variations of Sgr A∗
sion at 2 GHz have been detected. Using the cor- associated with the G2 event, we have conducted
relation amplitude of NRAO 530, and its X-band the ﬂux monitoring observations at X-band and S-IVS NICT-TDC News No.33

20

the mid-February to 16 August 2013 for 38 days,
and measured a very stable value of 0.48±0.05 Jy.
These monitoring observations are very importantfor studies black holes and AGNs. When the ﬂareis detected in our monitorings, we will alert it to
the world as soon as possible. We intend to continue these monitorings as often as possible until
at least May 2014.

10

Flux density [Jy]Sgr A*NRAO 530
1622-253
1622-297
1921-293

1

References
0.1
40

60

80

100

120

140

160

180

200

220

240

Day of year

Figure 5. Calibrated ﬂux densities of target sources
at X-band. These ﬂux densities are calculated byassuming that the ﬂux density of NRAO 530 is stable (3.3 Jy) during the observing period. Error bars
are 1σ standard deviation for each day.

[1] Ryu, S. G., et al. 2012, AIP, 1427, 284R
[2] Gillessen, S., et al. 2012, Nature, 481, 51[3] Gillessen, S., et al. 2013, arXiv:1306.13[4] Gas Cloud Wiki; Observing proposals for 2013(https://wiki.mpe.mpg.de/gascloud/ProposalList)[5] Bower, et al. 2006, ApJ, 648, L127

band with the NICT Kashima-Koganei VLBI system. We obtained the X-band ﬂux of Sgr A∗ from

September 201321

The Study of Time Synchro- for passing on t1 to Slave. Each message includes
time-stamp and one way delay and oﬀset are likenization over VPN
following respectively. Hence, propagation delay
and oﬀset are calculated like following respectively.
Yusuke Kito (y kito@fjtakalab.dnj.ynu.ac.jp),
Fujinobu Takahashi , Faculty of Engineering,
Yokohama National University
75-1, Tokiwadai, Hodogaya, Yokohama,
Kanagawa, Japan
Abstract: This paper presents the application of the
new time synchronization protocol, PTP (Precision
Time Protocol), and the veriﬁcation result of thatover the Internet. Some use NTP (Network Time
Protocol) for the time synchronization through theInternet, but NTP is not accurate enough for thesystems dealing with the time stamp like the ﬁnancial transactions, the industrial ﬁeld, and the next
generation communications. PTP is also called
IEEE 1588 and it will be of help in such situation.
We have veriﬁed the accuracy of PTP time synchronization over VPN (Virtual Private Network)and LAN (Local Area Network).
1.

= t2 − t1(1)= t4 − t3(2)
Dm2s + Ds2m
One way delay =2(t2 − t1 ) + (t4 − t3 )=(3)
2
Oﬀset = Dm2s − One way delay(t2 − t1 ) − (t4 − t3 )
(4)
=
2
Dm2s
Ds2m

where Dm2s is propagation delay from Master toSlave and Ds2m is that from Slave to Master. This
calculate is followed as the servo diagram as Figure 2 [3] and it samples propagation delay between
Master and Slave. This is based on equation 1 andequation 2.

Introduction

Time synchronization is popular technology for
us like NTP. A computer’s clock is managed by the
crystal oscillator on the motherboard. Since tt is
accurate but does not have enough stability, timesynchronization is used for that. PTP is the protocol for the hardware clocks synchronization thatis called IEEE 1588[1]. It is said that PTP is moreaccurate than NTP that is popular for us as thetime synchronization protocol. Although NTP is
not accurate enough for the systems dealing withthe time stamp like the ﬁnancial transactions. It isbecause that such systems have the computers exchange and storage the data including time stamp
and it is dealt with the data in increments of one
micro second. Hence PTP is the expected technology as the accurate time synchronization systemdealing with the time in increments of one nanosecond and it will be of help in such situation.
2.

PTP (Precision Time Protocol)

2.1

Basic Method

Figure 1 shows the basis of PTP timesynchronization[1]. As the ﬁgure Master sends
Sync Message to Slave, then Slave reply Delay Request Message to Slave and Master sends Delay Response Message to Slave. Using timestamps thesemessages include Slave calculates Propagation Delay and Oﬀset between Master and Slave as equation 3 and equation 4. Follow Up Message is used

Figure 1. Message Exchange

Figure 2. Clock Servo Diagram [3]2.2

Eﬀect of Asymmetric Network

It results of the calculation error of the oﬀset
between Master and Slave that Dm2s and Ds2m is
diﬀerent value. It is assumed that they are thesame value in PTP and NTP like Equation 4. If
Ds2m is equivalent with Dm2s + Δτ , the oﬀset isIVS NICT-TDC News No.33

22

calculated as following.
Dt2 − t 1= D + Δτ
= D+O

(5)
(6)

t4 − t3= D + Δτ − O(t2 − t1 ) − (t4 − t3 )
=
2
Δτ
= O−
2

(7)

Om

(8)
(9)

where D is Dm2s , D is Ds2m , Δτ is the diﬀerence Figure 3. The Experiment using M600/MRS andof D and D’, O is the authentic oﬀset, Om is the SyncBOX
measured oﬀset, and t1 , t2 , t3 , t4 are according to
Figure 1. In the end − Δτ
2 results in the calculation
error of the oﬀset.
3.2 over LAN
2.3

Eﬀect of Propagation Delay and Time
Synchronization Interval

Figure 4 shows the network construction ofthese experiments over LAN. Two computers,
The oﬀset is increasing during message ex- M600/MRS, and SyncBox in which PTPd is runchanges. It is assumed that the propagation delay ning are connected over LAN of the laboratory of
between Master and Slave is small enough for the Yokohama National University and the synchrooﬀset calculation in NTP and PTP time synchro- nization interval of PTPd is 30 seconds.
nization, and it is responsible if it is done over theLAN. The larger propagation delay is, the larger
the eﬀect of time synchronization interval as followings.
Oi=

Oi−1 + A · (t4 − t1 )

(10)

O

=

Om − A · (t4 − t1 )(11)

where Oi is the calculated oﬀset at the i-th timesynchronization and A is the drift of Slave clock
against Master. A · (t4 − t1 ) is the calculation error
component of time synchronization.
3.

Time Synchronization Experiment3.1

Overview

Figure 4. The Network Construction

Figure 5 shows the comparison of the time synWe have made four experiments that are of PTP
devices, M600/MRS and SyncBox made by Mein- chronization results using M600/MRS connected toberg Radio Clocks Gmbh & Co. KG[2], and two SyncBox and computers over LAN.
computers using PTPd installed by ”apt-get” command. M600/GPS and SyncBox are shown in
Figure 3. M600/MRS has a role as Master and
SyncBox has a role as Slave.
Note that the oﬀset between the computers extends about 10−5 seconds per second. Hence theoﬀset of such computers’ is extending a few seconds
per a day if each crock of a computer runs freely,
and in this paper we call the time synchronization between M600/MRS and SyncBox as hardware time synchronization and that between computers as software clock synchronization for conveFigure 5. Oﬀset Comparing over LAN
nience.

September 2013
3.3

23

over VPN

Figure 6 shows that over VPN. M600/MRS and
SyncBox are connected over VPN. In this situation
Master is in the laboratory of Yokohama National
University and Slave is in the room on the ﬁfteenth
ﬂoor of Yokohama Mitsui Building.

Figure 8. The Experiment through WINDS

Figure 6. The Network Construction
Figure 9. Oﬀset over WINDS Network
Figure 7 shows the time synchronization result using M600/MRS connected to SyncBox over
3.5
VPN.

Compiled Result

Table 1 and Table 2 are the compiled result of theabove ﬁgures using LSM (Least Squares Method).

Table 1. Result Comparing

Figure 7. Oﬀset over VPN

Accuracy [sec/sec]
Median [sec]Variance [sec]Hardware Clockover LAN
over VPN−2.78 × 10−12 4.33 × 10−9
4.87 × 10−6
2.70 × 10−4−6
4.81 × 10
8.22 × 10−2

According to Table 1, the all parameters overVPN
are worse than that over LAN. This means
3.4 over WINDS
that the larger the propagation delay and the ﬂucFigure 8 shows the network construction of the tuation component of that are, the larger these patime synchronization experiment using WINDS rameters are. Also according to Table 2, the allthat is the communication satellite launched by parameters over WINDS are worse than that over
JAXA, Japan, 2008. It shows the top level band- LAN. This results from the above, too.
width of Giga bit level and it has the function like a
network switching hub for the eﬀective data trans- 4. Summary
fer of the long-distance e-Medicen and e-Education.
We challenged and succeeded in the time synchronization over satellite network and VPN. In
Figure 9[4] shows the time synchronization result
the result, the accuracy and the median of timeusing computers over WINDS network.

IVS NICT-TDC News No.33

24

Table 2. Result Comparing
Software Clockover LAN
over WINDS−8
Accuracy [sec/sec] −2.16 × 10
−1.11 × 10−6
−4Median [sec]7.72 × 10
5.07 × 10−3
−2
Variance [sec]7.00 × 10
1.15 × 10−2synchronization are inﬂuenced by the propagation delay, and the variance of that is inﬂuenced
by the ﬂuctuation component of the propagation
delay. We will make the calibration system of
the time synchronization calculation error resulted
from that.
Acknowledgement
This experiment is supported by Takashi Takahashi, Toshio Asai, and Norihiko Katayama from
NICT (National Institute of Information and Communications Technology). I would like to show myappreciation for them.
References[1] “IEEE 1588-2008 Std.”, IEEE 1588 Standard
Board, 2008

[2] “Meinberg”, http://www.meinbergglobal.com[3] Kendall Correll, Nick Barendt, Michael Branicky: “Design Considerations for Software
Only Implementations of the IEEE 1588
Precision Time Protocol”, VTI Instruments,
2005,http://www.vtiinstruments.com[4] Yusuke Kito Satoshi Kubota, Fujinobu Takahashi, Takashi Takahashi, Toshio Asai, Norihiko Katayama: “First Challenge of PTP
Time Synchronization Experiment throughthe Experimental Satellite for Communication, “WINDS” ”, ISAP 2012, 2012.11

September 201325

Toward a Precise Frequency Current target of the accuracy of comparison−16
Comparison with VLBI Tech- over long distance is in the order of 10 in a few
days of interval. We will focus on more detail fornique
the high precise comparison by the VLBI techniquein this report.
Kazuhiro Takefuji (takefuji@nict.go.jp)1 ,Mamoru Sekido, Hideki Ujihara,
Thomas Hobiger, Masanori Tsutsumi,
Shingo Hasegawa, Yuka Miyauchi,
Ryuichi Ichikawa, Yasuhiro Koyama, andTetsuro Kondo
1

Kashima Space Technology Center, National
Institute of Information and Communications
Technology, 893-1 Hirai, Kashima, Ibaraki
314-8501, Japan

Abstract: We have been studying a frequency comparison technique using VLBI between distant stations. There are three important issues in our precise frequency comparison project with VLBI, one
is the use of a eﬃcient antenna and broad band receiver to obtain a good signal to noise ratio (SNR),
second is a highly stable and reliable signal transfer, third is solving time delay caused by the ionosphere and the atmosphere. These three issues
should be solved for precise frequency comparison
by using a VLBI technique. This report describes
some experiments to tackle to these issues.
1.

Introduction

National Institute of Information and Communications Technology (NICT) has been not only
developing VLBI observation system as the technology development center (TDC) of IVS, but also
taking a role of authority maintaining the JapaneseStandard Time (JST). Recently, the research on
atomic clock improvement is rapidly in progresses
in this ﬁeld. NICT, National Institute of Advanced
Industrial Science and Technology (AIST), andTokyo University have been developing an opticallattice clock for the next generation primary frequency standards and for the redeﬁnition of “theSecond”. Thus, it is becoming important to compare the distant clocks with several techniques. If
two stations are close in a few hundreds kilometer,
frequency transfer with optical ﬁber link [2] willbe the best way for that. However, for comparisons over inter-continental distances, techniqueswith space technologies such as GNSS, Two-Way
Satellite Time and Frequency Transfer (TWSTFT)
and VLBI are required.

2.

Broadband System in the VGOS Era

For the next generation of the geodetic VLBI,VLBI2010 Global Observing System (VGOS) has
speciﬁed a fast moving antenna and broad-bandreceivers. Some antennas, which meet with the
VGOS requirements, have been constructed, for example GGAO 12m antenna, 18 meter Westford in
the United States, TWIN Radio Telescope Wettezell (TTW) in Germany, the RAEGE telescopeat Yebes in Spain, and Ishioka in Japan.
Now NICT/Kashima has also been developing abroad-band system for 3 GHz – 14 GHz frequency
with the Kashima 34 meter diameter antenna andtwo small/transportable antennas. The broadband project is named “Gala-V”[1]. The system
has some features diﬀerent from other VGOS antenna. At ﬁrst, a feed horn for the 34m antenna,
which will be install until the end of this year,
has a sharp beam of 12 degrees half-power beamwidth. Secondly a direct sampler, which has 16
GHz sampling speed, is going to be used insteadof up-down converter. The direct sampler has four
DBBC channels of 1 GHz bandwidth, which is tunable up to 16 GHz. Current Gala-V system is going to use ﬁxed frequency array with 1 GHz bandwidth at 3.2 GHz, 4.8 GHz, 9.6 GHz, and 12.8 GHz.
These frequency interval selection was decided withtaking into account integer number of ratio 1:3:2 as
the no-redundancy array, which enables ﬁne delay
resolution with minimum side-lobes.
3.

For a Stable and Reliable Signal Transfer

VLBI observable is aﬀected by variety of causessuch as change of cable length of reference signaldelivery from Hydrogen maser and change of characteristics of electronic components in the signal
path from receiver to the sampler. Delay calibration signal (D-cal) and the phase calibration signal(P-cal) are used to calibrate the changes of the delays. The D-cal is used for monitoring the delaychange of reference signal delivery to the P-cal, andP-cal is used for the delay calibration in the signal
path to the sampler by injecting comb tone signal
in front of a low noise ampliﬁer.
The pseudo delay measurement result performed

IVS NICT-TDC News No.33

26

at Koganei 11 meter antenna is shown in Figure 1.
The pseudo delay was derived by Fourier transformation of the P-cal tones in 512 MHz band. Thatis equivalent with linear phase slope estimated byweighted least square. The magnitude of the variation was 80 pico second during about 4 hours. Figure 2 shows plot of temperature in the observation
room at Koganei station, which shows ﬂuctuations
with about 20 minutes of period. The two ﬁgure indicating that the behavior of the pseudo delay coincides with that of room temperature. This periodic
variation has not been awarded in the VLBI data
analysis so far, although the cause of this should
be investigated.

going to use 50 MHz for reference input to the Pcal in our Gala-V system. A reason of using 50
MHz reference is to gain the power of P-cal signal
at especially higher frequency. Generating uniform
P-cal signal in the wide frequency range is essential for the system. We conﬁrmed increasing thefrequency interval from 10 MHz to 50 MHz enables
generation of tone signal up to 15 GHz. Disadvantage of using 50 MHz reference signal is that P-cal
signal does not always appear in 32 MHz bandwidth, which is supposed to be a basic observation
mode in the VGOS. This is not the case for the
Gala-V, where 1024 MHz bandwidth for a single
channel. P-cal tone signal extraction is to be madevia software correlator, and it will be used for delay
calibration within the band.
-40
-45
-50

Amplitude [dBm]

-55
-60
-65
-70
-75
-80
-85
-90

Figure 1. Variation of pseudo delay derived from
P-cal tones over 512 MHz bandwidth in Koganei 11
meter antenna. Fluctuations with period of about
20 minutes are observed.

0

2000

4000

6000

8000
10000
Frequency [MHz]

12000

14000

16000

18000

Figure 3. The comb tones of digital P-cal output
in the case of 50 MHz reference input. Peak powerof tone signals of 50 MHz interval and that of 100
MHz interval are exchanged along the frequency.

4.

Fringe Phase for High Precision Delay
Monitoring

As one of the approaches to get high precisiondelay observable, using fringe phase with tracking
single radio source was examined. Table 1 shows
Figure 2. Temperature variation in the observation room of Koganei 11m station. Red and green
line indicates thermal monitor sensor output located near the VLBI back-end and room air, respectively. Fast temperature variation (fast risingand slow decay) must be caused by air conditioner.

Table 1. Speciﬁcations of VLBI observation

The Gala-V antennas are going to use P-cal device, originally designed by Haystack[3] and manufactured by A.E.S. Co. Ltd. Conventional P-cal
uses 5/10 MHz reference signal, although we areparameters of fringe phase VLBI observation withtracking the 3C84. A purpose of the observation
was to test extraction of ionospheric delay by using fringe phases, instead of combination of group

Baseline
Source
Date
Band
RecordCorrelator

Kashima 11m and Koganei 11m
3C84
2013/100, 16 hours
S/X (150 MHz / 512 MHz)
1 Gsps, 1 bit, 2ch
GICO3September 201327

delays at S-band and X-band which is used in theconventional geodetic VLBI.
There are four ways to obtain the ionospheric delay. One is to subtract the group delay among S/Xband conventionally. The second is to take diﬀerence between the phase delays of S and X bands.
However, it has only “relative” delay from initialone. The third uses an inverse feature between aphase delay and a group delay of X-band, and forthis the same with the third applied for S-band signal. The background theory of these features is
described below. Phase velocity vp is expressed byusing a wave number k and an angular frequency
ω as
ω
vp =
k
It is also shown as
vp =

c
n

Ionospheric delay Δτion can be derived from thediﬀerence of the phase delay and the group delay.
Hence
 L
 L
dl
dl
−
Δτion =
0 vg
0 vp

 L
1
1
=
−
dl
vg
vp
0

 L
vp − vg
dl
=
vp vg
0
Substituting vp vg = c2 ,Δτion =On the other hand,
vp − vgck
ω = kvp =
n

ωp =

ρq 2
0m

where q, m, and ρ are the electron charge, mass,and density, and 0 is the dielectric constant in a
vacuum. Hence
ck
ω= 
ω2
1 − ωp2
Finally ω can be expressed asω = c2 k 2 + ωp2
Then we get group velocity vg as
vg

∂ω
∂k
= cn

=

0

(vp − vg ) dlcAssuming ωp2 /ω 2  1, we get
vp − vg=c

Now we are thinking about the actual case in theionosphere for the geodetic VLBI observations. Inωp2=cthis case, ω is large enough compared with an anguω2
lar cyclotron frequency in the ionosphere. ThereTherefore
fore n can be approximated by neglecting cyclotron
frequency terms asΔτion =
ωp2
n= 1− 2=ω
where ωp is an angular plasma frequency and expressed as


 L


1
−n
n
⎛
⎞

ωp2
1
c ⎝
− 1− 2⎠ωp2
ω
1 − ω2==where c is the light speed in vacuum and n is a
refractive index of medium. Thus,

1
c2

1+

ωp2
ωp2
)
−
(1
−
2ω 2
2ω 2

 L

ωp2
dl
2
0 ω
 L
q2
ρdl
2
0 mcω
0

1
c

Total electron content (TEC) is expressed byL
0 ρdl, then we can get TEC as follows.
T EC =

0 mcω
q2

2

Δτion

Figure 4 shows ionospheric delay contribution
derived by four ways of the procedures describedabove. There are four combinations Sg − Xg ,Sp − Xp , Sp − Sg , Xp − Xg , where Sg and Xg indicate the group delays of S and X-band, and Sp and
Xp are the phase delays of those, respectively. Figure 5 shows the diﬀerence of total electron content(TEC) derived from the VLBI observation. Signal
to noise ratio of TEC measurement was better inorder of (Sp − Xp ), (Sp − Sg ),(Sg − Xg ), (Xp − Xg ).
Thus, ionospheric delay variation can be monitored
in best precision in the case using fringe phases. We
will pursue precise measurement of the atmosphericdelay by using the fringe phase also.

IVS NICT-TDC News No.33

0
-0.5
-1
-1.5
-2
-2.5
-3
-3.5
-4
-4.5
-5
4000

15
10
5
TECU

Delay [nsec]

28

0
-5
-10
-15

6000

8000

10000

12000

14000

Time [sec]

-20
4000

6000

8000

10000

12000

14000

Time [sec]Figure 4. Ionospheric delay derived by four waysof procedures described in the main text. The linesof pink, red, blue, and green colors are plots ofionospheric delay derived by (Sp − Sg ), (Sp − Xp ),(Xp − Xg ), and (Sg − Xg ), respectively. The last
one is the case of conventional VLBI. The lines
have adequately oﬀset to clearly seen.

5.

Summary

Figure 5. Total electron content (column density of electrons) derived by four ways of procedures. Vertical axis is indicated by TECU (1016electrons/m2 ). The lines of pink, red, blue, andgreen colors are plots of ionospheric delay derivedby (Sp − Sg ), (Sp − Xp ), (Xp − Xg ), and (Sg − Xg ),respectively. The precision of the measurement isthe best in the case using the phase delay diﬀerence
between S and X band.

We have been investigating technique using
VLBI for precise frequency comparison. Possi- References
ble error source of delay ﬂuctuations are examined[1] M.Sekido, Development of Wide-band VLBI
with P-cal signal. For using P-cal in the broadsystem (Gala-V), IVS NICT-TDC News No.
band Gala-V system, we are preparing P-cal using
33, pp.11–14, 2013.
50 MHz reference signal. Also D-cal system via
round-trip phase monitoring for 50 MHz reference [2] M.Fujieda, M.Kumagai, S.Nagano, Coherent
signal is under investigation. As a trial to improvemicrowave transfer over a 204-km telecom
the measurement precision, we conducted the sinﬁber link by a cascaded system, IEEETUFFC,
gle radio source tracking experiment, and derived
vol.57, no.1, pp.168-174, 2010.
the ionospheric delay contribution in four ways ofprocedures. We conﬁrmed that ionospheric delay [3] Rogers A.E.E.,Tests of new “digital”
phase calibrator, MIT Haystack BBDev
variation could be monitored in better precision by
Memo#023,
http://www.haystack.mit.
using phase delay than the conventional group detd/BBDev/023.pdf
edu/geo/vlbi
lay diﬀerence.

September 2013

29

Combination of space geodetic
techniques on the observationlevel with c5++

demanding goals of GGOS, a new analysis package
named ”c5++” has been developed. After veriﬁcation and comparison against other software packages, c5++ is currently being utilized for ultrarapid determination of UT1 by means of VeryLong Baseline Interferometry (VLBI) (Hobiger etThomas Hobiger (hobiger@nict.go.jp) andal. (2010) and has been used to demonstrate theToshimichi Otsubo
eﬀect of combining Satellite Laser Ranging (SLR)
and VLBI data on the observation level (Hobiger
National Institute of Information andand Otsubo (2013a)). The modularity of this analCommunications Technology
ysis software allows to process single technique so4-2-1 Nukui-Kitamachi, Koganei
lutions or combine the data on the observation
184-8795 Tokyo
level. As depicted in Figure 1, SLR, VLBI andJapan
Global Positioning System (GPS) modules sharethe same library which contains all geophysicalGeoscience Laboratory, Hitotsubashi University
models according to the latest IERS Conventions
2-1 Naka, Kunitachi(Petit and Luzum (2010). In addition, local tie in186-8601 Tokyo
formation can be included as virtual observations
Japan
which relat e between the technique- speciﬁc referAbstract: Multi-technique space geodetic analysis ence points.
software has been developed which allows to combine data on the observation level. This novel concept is being tested with SLR, GPS and VLBI data.
Results show that the combination of space geodetic data on the observation level leads to a consistent improvement of station position repeatability,
Earth orientation parameters, etc. Furthermore,estimation of common parameters (troposphere orclocks) at co-located sites helps to improve the solution further and derive an utmost physically consistent model of the concerned parameters.
Figure 1. The basic concept of c5++ allows to pro1. Introduction
cess single- and multi-technique space geodetic obCo-located space geodetic techniques can be servations by taking advantage from the usage offound at so-called fundamental sites. At such sta- identical geophysical models.
tions two or more techniques are operated side byside and the reference points of the individual space
geodetic instruments are connected by precise local tie measurements. Thus space geodetic datafrom diﬀerent techniques can be combined for the
purpose of reducing systematic (instrumental) effects. However, until now combination is mostly
being done either on the level of normal equations
or on the level of results. Even if space geodetic
techniques are analyzed with the same geophysicaland mathematical models, only a combination on
the observation level can ensure a consistent usageof all observational data. Therefore, combinationon the observation level is one of the goals for therealization of the Global Geodetic Observing System (GGOS) as described by Plag and Pearlman(2009).

2.1

Other than combination of space geodetic results, where parameters are derived individuallyfrom each technique, combination of all available
space geodetic observations on the observationlevel is expected to obtain more robust parameters.
Outliers are less likely to bias the solution as datafrom other techniques helps to identify such data
artifacts. Moreover, clock and troposphere parameters at co-located sites need to be estimated only
once, which further stabilizes the geodetic solutions
and avoids that data artifacts are absorbed in suchnuisance parameters.
2.1.1

2.

Space geodetic data analysis with c5++

Combination on the observation level

Prerequisites

Although combination on the observation levelisstraightforward with respect to the mathematDriven by the need to update existing space
ical
formulation, one needs to make sure thatgeodetic analysis software and motivated by the

30

IVS NICT-TDC News No.33

where Dhz and Dwz are hydrostatic and wet zenith
delays with the corresponding mapping functions
mh (ε) and mw (ε) which depend on the elevation
angle ε. Horizontal gradients in North- (GN ) andEast-direction (GE ) allow to consider azimuthal(α) asymmetry and are mapped with a dedicatedgradient mapping function mg (ε). Since hydrostatic delays can be computed a-priori with sufﬁcient precision, one needs to estimate only wet
zenith delays, respectively gradient parameters. If
Figure 2.
.
Co-located space geodetic tech- another microwave technique, e.g. VLBI, is coniques and the possibilities for combining them di- located with the GPS antenna, one can assume that
rectly(i.e. local-ties) or implicitly (i.e. by estimat- troposphere conditions are almost identical, i.e.
ing common parameters).
(2)
τV LBI (ε) = τGP S (ε) + mh (ε)ΔDthe underlying (geo-)physical models are consistentamong the diﬀerent techniques. c5++ has been designed to ensure these requirements. However, estimation of a common troposphere model requiresthat a-priori hydrostatic delays are derived fromconsistent meteorologic data-sets. VLBI stations
are usually equipped with ground meteo sensors,
whereas such technology is not always deployedat GPS sites. Thus, VLBI meteo data has to be
replaced with consistent meteorologic information
which is also used for GPS processing and whichallows to model the troposphere tie as a daily constant oﬀset. This can be achieved by processing
both, VLBI and GPS data, with the GPT2 model.
Troposphere gradients can be assumed to be identical as long as the distance between the co-locatedtechniques does not exceed a few kilometers, a criteria which is met at all fundamental sites. In addition to consistent a-priori models, one needs tomake sure that inter-technique parameters are estimated with the proper temporal resolution. As
discussed in the prior section, troposphere ties ΔD
can be estimated as a constant oﬀset over 24 hours.
However, inter-technique clock diﬀerences ΔL(t)should be parameterized with a temporal resolution that allows to model at least a diurnal variation, which is the dominant signal caused by temperature dependent cable length variations.

where the last term considers the height diﬀerence
between the space geodetic instruments, whichcauses a small hydrostatic zenith delay ΔD. Estimating this so-called ”troposphere-tie” as a daily
constant value together with the other unknowns
allows to obtain a single set of troposphere parameters for each space geodetic co-location site.
In addition, one can estimate a common clock
model, if signals from a frequency standard are distributed to both systems, i.e. feeding the GPS receiver and steering the VLBI back-end. However,when expressing the relation between the VLBI
and the GPS clock in the form
clockV LBI = clockGP S + ΔL(t).

(3)

one needs to take into account that electrical cable
lengths and VLBI equipment cause the oﬀset term
ΔL(t) to be time-dependent.
In contrary, combination of SLR and microwave
based space geodetic techniques does not have any
advantages for such nuissance parameters. However, if the same satellite is tracked by SLR andGPS, it is possible to estimate its orbit by combining the data from both techniques on the observation level. c5++ does not oﬀer the possibility
to estimate GPS orbits at the moment, but such a
feature is expected to be implemented until the endof this ﬁscal year. Although combination of VLBI
and SLR, as shown in section 3.2, does even have
2.1.2 Common parameters
the possibility to estimate such common parameters, it is shown that the introduction of local-tie
Microwave based techniques like the Global Poinformation alone is suﬃcent to improve the station
sitioning System (GPS) or VLBI have in common
coordinate estimates.
that the neutral atmosphere (troposphere) causes
signals to be delayed since the refractivity index of 3. First results with c5++
the gases in the media is not equal to one. FollowIn order to study the combination of space geodeing Davis et al.(1993), one can model the tropotic
data on the observation level impacts the target
sphere excess delay for GPS in the form
parameters and helps to stabilize nuissance paramτGP S = mh (ε)Dhz + mw (ε)Dwz
eters, two diﬀerent cases were studied. First, VLBI
+mg (ε)(GN cos α + GE sin α), (1)September 201331

and SLR data have been combined on the observation level at at single site, i.e. TIGO at Con- Table 1. Mean station position repeatabilities (incepcion/Chile. In doing so, only local-tie informa- mm) from the ﬁve diﬀerent solutions (see text).
N/S E/W U/D 3D
sol.
tion could be used to connect the two techniques.
S0001
2.74 4.65
8.11 9.97
For the second test scenario, VLBI and GPS were
1.46
2.35
4.12 5.12
S0010
combined, using the suggested common parameter
S0011
1.40
2.24
4.00 4.95
set-up from section 2.1.2.
S0111 1.33 2.13
3.93 4.82
3.97 4.81
S1111 1.28 2.07
3.1 Combination of SLR and VLBI at
TIGO
Fig. 3 shows the East component of the estimated SLR-only, VLBI-only and combined coordinate time series after the 2011 Earthquake, whichshifts TIGO by almost 4 m westwards with respect to its original ITRF position. Both, formal
errors and the scattering of the time series are signiﬁcantly reduced when combining SLR and VLBI
data. Thus, the underlying geophysical signal withits main component of a slowly decreasing Eastward plate velocity becomes very clear in the timeseries of the combined approach. SLR and VLBI
results reveal a similar behavior, however the relatively large scattering between consecutive 10 day
batches makes it diﬃcult to see the exponential decrease of the post-seismic velocity. Although combination of space geodetic data improves the accuracy of the results, it happens that the estimate forthe ﬁrst 10 day batch in December 2010 can not beseen in the combined solution. A further discussion
about this analysis and the impact of combinationon the observation level on SLR and VLBI relatedparameters can be found in Hobiger and Otsubo(2013a).
3.2

Combination of GPS and VLBI during
CONT11

Table 2. RMS of the diﬀerences between the estimated EOPs and those from the IERS-C04 timeseries (see text).
sol.
UT1
Xp
Yp
[μsec] [μarcsec] [μarcsec]
S0001 10.59
74.53
79.10
S0011 11.29
76.35
53.14
46.73
62.96
S0111 10.11
S1111
9.81
46.54
60.93
site-dependent parameters as well. In all solutions
earth orientation parameters (EOPs), i.e. UT1and pole coordinates (Xp /Yp ), were only estimatedfrom VLBI data since GPS orbits were kept ﬁxed.
Station position repeatabilities, measured as root
mean square (RMS) error, during the 15 day period are computed for each solution and then averaged over all network sites (Table 1). As expected,
VLBI-only station position repeatability is worse
than the GPS-only solution. In general, scattering of the VLBI-only solution is about twice aslarge as the GPS single-technique position results.
However, once data are combined on the observation level and local tie vectors are added as virtual
observations, co-located VLBI and GPS sites reveal the same stability. Estimating the troposphereconditions as site-dependent common parameters,
as done in solution S0111, has another positive impact on the station position repeatability. T heestimation of both, common troposphere and clockparameters, as carried out in solution S1111, yields
the best performance among all solution strategies. Table 2 summarizes the RMS of the EOP
estimates w.r.t. the IERS-C04 time-series. It canbe seen that solution S1111 performs much better
than the VLBI-only analysis, showing an improvement in RMS of about 7 % RMS for UT1 as well as
37% and 23% for the pole coordinates respectively.
An in-depth discussion of this results can be foundin Hobiger and Otsubo (2013b).

In total 14 VLBI stations joined the CONT11,a campaign of continuous VLBI sessions observed
between Sep. 15th and Sep. 30th 2011, network.
However, since not all stations continuously contributed to CONT11 and only a fraction of the
network station shared a common frequency standard with the co-located GPS receiver (Rieck etal. (2012)) only 7 stations remain which can beused for combination of GPS and VLBI. A VLBIonly (S0001) and a GPS-only PPP solution (S0010)
were compute for reference. The ﬁrst solution
which combines GPS and VLBI on the observation level, i.e. S0011, only added local tie vectors as virtual observations that relate between
the reference points of the co-located VLBI and
GPS antennas. Taking this concept a step fur- 4. Discussion
ther leads to solution S0111, which includes theIt could be shown that combination of spaceestimation of site-dependent troposphere paramegeodetic
data on the observation level improves
ters. The last solution (S1111) extends this apboth,geodetic
target parameters and nuisanceproach further and deals with clock estimates as

IVS NICT-TDC News No.33

32

[m]

SLR E/W
-3.6
-3.65
-3.7
-3.75
-3.8
-3.85
-3.9
-3.95
-4

SLR only2010-Apr

2010-May

2010-Jun

2010-Jul

2010-Aug

2010-Sep

2010-Oct2010-Nov

2010-Dec

2011-Jan

2011-Feb

2010-Oct2010-Nov

2010-Dec

2011-Jan

2011-Feb

2010-Oct2010-Nov

2010-Dec

2011-Jan

2011-Feb[m]

VLBI E/W
-3.6
-3.65
-3.7
-3.75
-3.8
-3.85
-3.9
-3.95
-4

VLBI only
2010-Apr

2010-May

2010-Jun

2010-Jul

2010-Aug

2010-Sep[m]

Combined E/W
-3.6
-3.65
-3.7
-3.75
-3.8
-3.85
-3.9
-3.95
-4

SLR (combined)
VLBI (combined)
2010-Apr

2010-May

2010-Jun

2010-Jul

2010-Aug

2010-Sep

Figure 3. E/W components of post-seismic site displacements at TIGO from SLR-only, VLBI-only andcombined solutions.

parameters like troposphere estimates. Parameters estimated from the combined approaches performed better than any of the single-technique solutions. In addition, outliers are less likely to mitigate into parameters when more than one space
geodetic technique is used to estimate physically
identical quantities like troposphere or clock oﬀset.
One can extend this concept and combine all threespace geodetic techniques and estimate orbit parameters as well. In doing so, GPS satellites which
are also tracked by SLR sites would increase thenumber of implicit links between the techniques
and further improve the estimation of target parameters. Thus combination of space geodetic dataon the observation level appears to be a promisingstrategy to support the GGOS goals and help to realize the next generation of reference frames which
are requir ed for monitoring global change.

References
Davis J.L, G. Elgered, A.E. Niell, C.E. Kuehn (1993),
Ground-based measurements of gradients in the”wet” radio refractivity of air, Radio Science, 28(6),1003–1018
Hobiger T., T. Otsubo, M. Sekido, T. Gotoh, T. Kubooka, H. Takiguchi (2010), Fully automated VLBI
analysis with c5++ for ultra-rapid determination of
UT1, Earth Planets Space, 45(2), 75–79.
Hobiger T. and T. Otsubo (2013a), Observation Level
Combination of SLR and VLBI with c5++: a casestudy for TIGO, submitted.
Hobiger T. and T. Otsubo (2013b), Combination of
GPS and VLBI on the observation level — prerequisites, functional models and results, in preparation.
Petit G. and B. Luzum (2010), IERS Conventions(2010), IERS Technical Note 36, 179 pp.
Plag H.P. and M. Pearlman (2009), The Global Geodetic Observing System: Meeting the Requirements ofa Global Society on a Changing Planet in 2020, Geoscience Books, Springer Berlin.
Rieck C., R. Haas, P. Jarlemark, K. Jaldehag (2012),
VLBI frequency transfer using CONT11, European
Frequency and Time Forum (EFTF), 163–165.

September 201333

New Project for Constructing a individual performance of the other equipments,
especially analog devices, which are already comVLBI2010 Antenna in Japanplete.
Yoshihiro Fukuzaki (fukuzaki@gsi.go.jp),
Tadashi Tanabe, Jiro Kuroda,
Shinobu Kurihara, Ryoji Kawabata,
Takahiro Wakasugi
Geospatial Information Authority of Japan
Kitasato-1, Tsukuba, Ibaraki, Japan
Abstract: The Geospatial Information Authorityof Japan (GSI) has started a new project for constructing a VLBI2010 antenna (radio telescope) inJapan. The basic design of the speciﬁcation of
the antenna has been complete, and the antenna
is now being constructed. The other equipments
are almost complete and delivered to GSI. The observation system will be fully compliant with the
VLBI2010 concept. The site candidate of the station for a new antenna is near Tsukuba. The antenna will be installed in the site by the end of thisﬁscal year.
The progress of the construction of the new antenna and the individual performance of the otherequipments, which are already delivered to GSI,
are brieﬂy reported.
1.

Introduction

The Geospatial Information Authority of Japan(GSI) has carried out VLBI observations since1981. In the ﬁrst period from 1981 to 1994, wedeveloped transportable VLBI systems with a 5m antenna and a 2.4-m antenna, and carried out
domestic observations by using them. As a result,
8 sites in Japan were observed and precise positions determined. In addition, Japan-Korea VLBI
observations were carried out by using a transportable 3.8-m antenna in 1995. In these observations, the Kashima 26-m antenna, which was removed in 2002, was used as a main station. Next,
in the second period from 1994 to 1998, GSI established four permanent stations: Tsukuba 32m, Sintotsukawa 3.8-m, Chichijima 10-m and Aira
10-m antennas. Up to the present, regular VLBI
observations by using the four stations have been
carried out. Especially, Tsukuba 32-m antenna isa main station for not only domestic but also international VLBI observations now.
In 2011, GSI started a project for constructing
a new antenna following the VLBI2010 concept,
which is recommended by the International VLBI
Service for Geodesy and Astrometry (IVS) as thenext-generation VLBI system.
This paper gives the outline of the project, thedesign speciﬁcations of the new antenna and the2.

Observing Facilities

In the new project, observing facilities will be
constructed. The conceptual design consisting of
the six components is depicted in Figure 1. The
temporary operations room will be installed instead of the Operations Building.
3.

Components

3.1

Antenna

The antenna (radio telescope) is the main part ofthe observing system. Since a single antenna will
be employed, very high slew rates are speciﬁed inorder to be compliant with the VLBI2010 concept.
The design speciﬁcations of the antenna are listed
in Table 1.
3.2

Front-end

According to the VLBI2010 concept, a wideband feed is necessary to achieve high aperture eﬃciency over 2–14 GHz. At present the Eleven feed,
which has been developed at Chalmers Universityof Technology in Sweden, is one of the practicalfor wide-band receiving. In addition, QuadrupleRidged Fared Horn (QRFH), which has been developed by California Institute of Technology (Caltech), is also suitable for wide-band receiving. As aresult, these two types of feeds are delivered to GSI.
The employment of the feed will be determined after the evaluation of the antenna performance withthese two feeds. For the design of the antenna optics, employing the Eleven feed is assumed.
The feed and Low Noise Ampliﬁers (LNAs) areintegrated into the cryogenic system, whose physical temperature is less than 20K. The system noise
temperature will be less than 40K (excluding atmospheric contributions).
Preliminary results of the measurements of thereceiver noise temperature for QRFH system areshown in Figure 2. In the case of both polarizations, the noise temperature is almost less than
30K. (The spikes are caused by RFI.)
On the other hand, the Tri-band feed system will
be installed by replacing the wide-band receiving
system with it in order to perform legacy S/X band
observations with Tsukuba 32-m antenna and theother legacy antennas.
The phase and cable calibration system will also
be installed. A new type of P-cal unit is underdevelopment. In addition, instead of the present
D-cal a new cable calibration system is also underIVS NICT-TDC News No.33

34

Antenna side

Operations Room side

3. Up-Down Converter

2. Front-end

4. Data Processing &Acquiring System

1. Antenna
5. Precise Frequency Standard(H-maser)(6. Temporary Operations Room)Figure 1. Conceptual design of the new observing facilities

Figure 2. Receiver noise temperature for QRFH system (Upper: Horizontal polarization, Lower: Verticalpolarization.)September 201335

Table 1. Design speciﬁcations of the new antenna.
Parameter
Diameter
RF frequency range
Surface accuracy
Aperture eﬃciency
Antenna noise temperature
System G/TAZ maximum slew rate
EL maximum slew rate
AZ maximum acceleration rate
EL maximum acceleration rate
Cable for signal transfer
Special feature

Value
13.2 m
2–14 GHz≤ 0.4 mm (rms)≥ 50%≤ 10K (excluding atmospheric contributions)≥ 45.882 dB (at 14 GHz)
[T is the system noise temperature (Tsys), and Tsysexcluding antenna noise temperature should be assumed
as 30K.]≥ 12◦/sec≥ 6◦/sec≥ 3◦/sec2≥ 3◦/sec2
Optical ﬁber cable from antenna to building
Reference point should be measured directly from theground for co-location.

Table 2. Speciﬁcations of the front-end.
Parameter
RF frequency range
Polarization
Feed
Dewar
Physical temperature
System noise temperature
Total gain
Output frequency range
Number of output
Phase and delay calibration
Injection of P-cal/noise-source

Value
2–14 GHz
Dual linear polarization
Equivalent for Eleven feed or moreFeed, LNAs, and other devices should be included andcooled by cryogenic system.
≤ 20K≤ 30K (excluding antenna noise temperature)≥ 45 dB
2–14 GHz
2 (for dual linear polarization)
New-type P-cal unit
New cable calibration system developed by NICTIn the front of the feeddevelopment. The speciﬁcations of the front-end 3.4 Additional Facilities
are shown in Table 2.
Optical ﬁber cables will be installed at the newsite
in order to establish a high-speed data link for
3.3 Up-Down Converter
data transmission. Initially, the transmission rate
In order to convert the observed analog signal to will be 10 Gbps; then it will be increased to 32
digital data, the frequencies should be downcon- Gbps and more in the future.
verted. For this purpose, a new Up-Down ConA Global Navigation Satellite System (GNSS)
verter is developed. The output signal frequencies continuous observation system will be installed atare 1–2 GHz. The Lower Side Band (LSB) and Up- the new site to be registered as an IGS (Internaper Side Band (USB) need to be selectable in the tional GNSS Service) station.
Up-Down Converter, because the second Nyquist
zone will be used in the sampler (see Kurihara 4. Candidate Site[2013]). The speciﬁcations of the Up-Down ConThe site candidate for a new station is nearverter are given in Table 3.
Tsukuba (about a 50-minutes drive by car). The

IVS NICT-TDC News No.33

36

Table 3. Speciﬁcations of the Up-Down Converter.
Parameter
Input frequency range
Output frequency range
Type of output signal
Number of units
Number of channel per one unit
1st local oscillator
2nd local oscillator
Total noise ﬁgure
Phase stability

Value
2–14 GHz
1–2 GHzLSB or USB (selectable)
4
2 (for dual linear polarization)
Programmable with 0.4-MHz step
2 ﬁxed LOs for LSB and USB≤ 25 dB≤ 4◦ with ± 2◦ C temperature change

Figure 3. Location of the candidate site of the new observing facilities.
location is shown in Figure 3. According to the Reference
results of a soil investigation of the site, there is
bedrock very close to the surface (at less than 3-m Kurihara S., VLBI2010 – Newly Established VLBI Station –, IVS NICT Technology Development Center
depth).
News, No.33, pp.37–38, 2013.

5.

Summary

A new project for constructing a new antenna inJapan has started. The basic deﬁnition of the speciﬁcations has been accomplished. The new station
will be fully compliant with the VLBI2010 concept.
The construction of the station will be complete by
the end of March 2013. After completion of thestation, it will play an important role as a main
station in the Asian region.

September 201337

VLBI2010 – Newly Established
VLBI Station –Shinobu Kurihara (skuri@gsi.go.jp)
Geospatial Information Authority of Japan
1 Kitasato, Tsukuba, Ibaraki 305-0811, Japan
Abstract: The Ishioka VGOS station is a newly established VLBI station of the Geospatial Information Authority of Japan. In this report, a set ofthe digital back-ends (DBE) together with a hugedata storage system and a pair of hydrogen masers
delivered by last March are brieﬂy described. At
the later half, the current situation of the construction and planning of VGOS staions in the world isreported.
1.

Introduction

In 2011 ﬁscal year, the Geospatial Information Authority of Japan (GSI) decided to build
a new VLBI2010 concept station. The International VLBI Service for Geodesy and Astrometry(IVS) named such a new station VGOS; VLBI2010
Global Observing System. The site of the Ishioka
VGOS station is located 17 km northeast of the
Tsukuba 32-m antenna, and the telescope will bebuilt on a basement outcrop at the top of the small
hill in the site of the Ibaraki Prefectural LivestockResearch Center. The station will consist of a radio telescope, three alternative front-end systems,
a ﬂexible up-down converter (UDC), a set of thedigital back-ends (DBE) together with a huge data
storage system, and a pair of hydrogen masers. By
the end of March 2013, all equipment except theantenna was already delivered to GSI. The DBE
and hydrogen masers are reported in the next section. For the report of other equipment, see thearticle of Fukuzaki, et al. in this letter.
2.

Delivered devices

2.1

Data Acquisition System

Figure 1. K6/iDAS sampler units in lack.
‘burst mode’ data acquisition. There is no removable disk; instead a 440-TByte total eﬀective capacity RAID system is mounted for storage. Since
Ishioka station will be linked to an external network with 10 GigE provided by SINET4, e-transfer
is assumed for data transfer.

As a data acquisition system for VLBI2010 operation, a set of DBEs, Linux servers and a storage system was installed (Fig.1 and 2). The DBE
is regarded as a successor of the Japanese VLBI
systems like K4 and K5, and named as K6/iDAS(K6/Intelligent Data Acquisition and Streaming
sampler). It is capable of 4-Gsps/2ch samplingwith 8-bit quantization, DBBC function up to 32
channels with FPGA, and 4 Gbps/ch of maximum
data rate by 10-GigE output. The 32-Gbps data
rate that is a full VGOS recording (32 Gbps = 1GHz bandwidth, 2 polarizations, 2 bit, and 4 chan- Figure 2. 18 Linux servers and a data storage sysnels) is available with four K6/iDAS units. The tem.
Linux servers and data storage system, which function as a recorder, are able to record 32-Gbps data
stream from four DBEs without RAM buﬀer inIVS NICT-TDC News No.33

38

2.2

Hydrogen Maser

A pair of hydrogen masers VCH-1003M produced by the VREMYA-CH in Russia was delivered (Fig.3). They have 5, 10, 100, and 1400 MHz
frequency standard output ports and two 1pps output ports. The frequency stability (allan deviation)is 2e-15 for 1000 sec. The frequency distributor,
GPS receiver with Rb oscillator for time synchronization, remote monitoring and controlling systemwere developed and installed by a manufacturer inJapan. If one maser in operation has trouble, theother alternatively be switched from remote placeby the remote controlling system. In preparation
for power outage, the masers have the 12-hour UPS Figure 4. VGOS stations in the world as of Marchbatteries.
2013.
The Instituto Geograﬁco Nacional (IGN) in
Spain is constructing a 13.2-m dish antenna at
Yebes. It is a part of Spanish and Portuguese
project RAEGE, and the Atlantic VLBI network will be completed with Santa Maria, Flores(Azores), and Tenerife (Canary Island).
In Russia as well, 4-station VGOS network isplanned, and the construction will begin in 2015.
The Shanghai Astronomical Observatory (SHAO)
has obtained enough budget to construct three
VGOS stations in China. The selected sites are
Shanghai, Urumuqi, and Changchun. Other thanthat, Sweden and Norway are respectively planning
the twin telescope construction. Many countries in
the world are proceeding their VGOS project.
4.

Summary

In the Ishioka VGOS station project, all equipment except the antenna was delivered by March
2013. We developed and installed the data acquisition system called K6/iDAS consistent with the
Figure 3. Hydrogen masers and remote monitoring full VGOS operation. Meanwhile, the constructionof the telescope is ongoing. That will be completed
and controlling system.
by March 2014.
After the inauguration of the Twin Telescope
Wettzell, many countries; Spain, Russia, China,
3. VLBI2010 Situation in the World
Sweden, and Norway are proceeding the VGOS
Since the release of the progress report of project in each country.
VLBI2010 Committee of IVS [1], VGOS stations
are being constructed and planned in many References
countries (Fig.4). In Germany, the Bundesamt [1] Petrachenko, B., A. Niell, D. Behrend, B.
für Kartographie und Geodäsie (BKG) completed
Corey, J. Böhm, P. Charlot, A. Collioud, J.
the Twin Telescope Wettzell (TTW) with 13.2-m
Gipson, R. Haas, T. Hobiger, Y. Koyama, D.
dishes. The inauguration ceremony was held on 26
MacMillan, Z. Malkin, T. Nilsson, A. Pany,
April, 2013. The state secretary of Federal MinG. Tuccari, A. Whitney, J. Wresnik, Design
istry of the Interior, Cornelia Rogall-Grothe andAspects of the VLBI2010 System, Progress
the president of the BKG, Hansjörg Kutterer, andReport of the IVS VLBI2010 Committee,
some guests were invited. Now a movie includingNASA Technical Memorandum NASA/TMﬁxed point photographing of its construction
2009-214180, 2009.
is available on the BKG website; http://www.
bkg.bund.de/nn 147094/DE/Aktu/01Meldungen/M2013/2013-04-30 Twin-Teleskope.html(cited on June 11, 2013).

September 2013

39

Developments of K3, K4, and Key Stone Project (KSP) from 1994 to 2001 anddevelopments of the K4 system were further
K5 VLBI Systems and Consid- theperformed. In the same period, ISAS conductederations for the new K6 VLBI the VLBI Space Observatory Programme (VSOP)
and used the K4 System for observations and data
Systemcorrelation processing. The developments of theYasuhiro Koyama (koyama@nict.go.jp)
National Institute of Information andCommunications Technology,
4-2-1 Nukui-Kitamachi, Koganei, Tokyo
184-8795, Japan
Abstract:
Historically, systems for VLBI observations anddata analysis developed at Kashima Space Research Center have had codenames starting withthe letter ’K’. Whereas K1 and K2 systems are experimental systems to demonstrate the capabilities
of VLBI as an observation method, the successive
series starting from K3 are practical systems routinely used for domestic and international VLBI
sessions. In this report, the history of the developments of the K3, K4, and K5 VLBI systems arereviewed and considerations about the K6 VLBI
system are presented.
1.

Introduction

At Kashima Space Research Center of the National Institute of Information and Communications Technology (NICT), observation and dataprocessing systems for VLBI have been designed
and developed. In the 1980s, when the institutewas called Radio Research Laboratories (RRL), theK3 VLBI system was developed as the ﬁrst complete Japanese VLBI system to support both observations and data analyses. By using this system, global and domestic geodetic VLBI observations were performed under the Crustal Dynamics Project and other campaign projects conductedby international organizations or through institutional collaborations. The K3 VLBI system wasadopted by Geospacial Information Authority ofJapan (GSI), whose name was Geodetic Survey Institute at that time, and was used for more than 10
years for Geodetic and Astronomical VLBI observations at many VLBI observing stations in Japan.
The developments of the K4 VLBI system werestarted in the late 1980’s to expand the observation
capabilities and to improve the operational functions. The K4 VLBI system was adopted by GSI,
National Astronomical Observatory of Japan, National Institute of Polar Research, and Institute ofSpace and Astronautical Science (ISAS). NICT, atthat time the name of the institute was Communications Research Laboratory (CRL), conducted

K5 VLBI System were motivated by the idea to use
conventional PC systems for data acquisition andcorrelation processing. The ﬁrst K5 data sampler
board and a group of software correlation programs
were developed since 2001. The K5 VLBI Systems enabled VLBI observations and data analysis
by smaller groups in universities and also stimulated the e-VLBI realtime/quasi-realtime observations over the public Internet. In this report, thecharacteristics and capabilities of the K3, K4, andK5 VLBI Systems will be reviewed, and in addition, the ideas and plans for new K6 VLBI System
will be presented.
2.

K3 VLBI System

The recording system of the K3 VLBI system was designed to maintain compatibility with
the Mark-III VLBI system developed mainly by
Haystack Observatory of the Massachusetts Institute of Technology in the United States. By using the K3 VLBI System, which is partially shownin the Figure 1, it became possible for the 26m antenna VLBI station at Kashima to participate international geodetic VLBI sessions. Regular VLBI observations began from 1983 and it
was soon conﬁrmed that the distance between the
Kashima 26-m VLBI station and the Kokee Park
VLBI station in Kauai, Hawaii, USA, is decreasing due to the motion of the Paciﬁc Plate withrespect to the North American Plate. All of thesystems necessary for VLBI observations were independently performed by the team in RRL withcooperation with Japanese vendor companies. Hydrogen maser system was developed to produce
standard frequency signal to be used as a reference
for frequency conversion of received signal, and for
A/D sampling in the K3 Formatter. The longitudinal open-reel high speed recorder was designed
to be compatible with the Mark-III recorder. This
was, the data tapes recorded with the K3 Recordercould be read with the Mark-III Recorders at
Collerator Centers in the United States of America
and in Germany (Kunimori, et al., 1993).
3.

K4 VLBI System

In the 1990s, a new VLBI observation and dataprocessing system was developed as the K4 VLBI
system. The developments were performed mainly
under the Western Paciﬁc VLBI Project whichstarted in 1988 and the Key Stone Project which

40

IVS NICT-TDC News No.33

Figure 1. This picture shows observing part of
the K3 VLBI System at observing station. The
hydrogen-maser system for the frequency standard,correlator, data analysis and database systems are
not shown in this picture.
started in 1994. The K4 VLBI system was designed
to improve the sensitivity of the VLBI observations
and the transportability of the system. For these
purposes, a compact and high data rate recording system based on a helical scan recording head
unit was adopted. The main concept of the developments of the K-4 VLBI observation and data
analysis system was to minimize required humanoperations and to maximize operational reliability
and durability. For the KSP VLBI Network system, a lot of technological challenges were madeand realized. Figure 2 shows pictures of the K-4
observation system at observing stations and K-4
correlator system at Kashima Space Research Center.
The K-4 data recording system does not require
frequent maintenance procedures and can recordand reproduce observation data at the total data
rates of 64 Mbps, 128 Mbps, and 256 Mbps withthe bit error rate of less than 1 × 10−10 becauseof its robust error correction capability. The D1 standard cassette tapes used to record the data
are easy to handle and to transport. Using the tapechanger unit with the K-4 data recorder unit, data
recording can be continued up to 24 tapes which
are equivalent to 20 continuous hours at the data
rate of 256 Mbps. The correlation processing andthe following data analysis procedures were also
automated. Once the all observation tapes whichwere recorded during a VLBI session are set in thetape changer units of the correlator system, data
correlation processing and data analysis are performed automatically without any human operations. With these systems, routine VLBI sessions
were performed every day and the results of data
analysis were placed on the WWW server within
two days. Later in 1997, the data recording sys-

Figure 2. Pictures of the K4 VLBI Systems. (a)Observation parts of the K4 VLBI System at theobserving station. (b) DIR1000 K4 recorder unit,
DFC1100 Input Interface Unit, Video Converter
Units and Local Oscillator Unit. (c) K4 hydrogen maser system. (d) K4 Correlator system for
4 stations 6 baselines.
tem was replaced with the high speed data transmission system using the high speed network andthe real-time VLBI observations were realized (Kiuchi et al., 2000). With the real-time VLBI system, almost continuous observations at the data
rate of 256 Mbps became possible and the analysis
results were actually produced immediately after
each observing session (Kondo et al., 1998). Since
all procedures from the observation at the observing stations through the data analysis processing
are completely automated (Koyama et al., 1998).
After realizing high speed data sampling anddata recording at 256 Mbps were achieved, further improvements were pursued by adopting giga-

September 201341

the VLBI Standard Interface (VSI) speciﬁcations(Nakajima et al., 2001).
4.

Figure 3. K5 VLBI Systems. (a) The initial version of the A/D sampling board K5/VSSP. (b)K5/VSSP32 system is interfaced with a PC running on Debian Linux operating system by a USB
serial bus. (c) ADS1000 A/D sampler unit. (d)ADS2000 A/D sampler unit. (e) ADS3000 A/D
sampler unit.
bit recorder unit GBR1000 based on the D6 cassette tape format. The GBR1000 recorder is interfaced to high speed sampler unit ADS1000 throughK5 VLBI System

In contrast to the K4 VLBI system, which wasdeveloped with the specially designed high-speed
cassette tape recording system, the K5 VLBI system can be characterized as a system designed withthe commodity products such as personal computers, hard disks, and network components. This
strategy was quite successful since both high ﬂexibility and high performance have been realized inthe VLBI observation and data processing system.
We have developed two independent series of systems as the data acquisition terminal of the K5 system as shown in the Figure 3. One is the K5/VSSP(versatile scientiﬁc sampling processor) system series (Kondo et al., 2003; Kondo et al., 2008) and theother is the K5/VSI system series (Koyama et al.,2003). The K5/VSSP system and its next generation K5/VSSP32 system comprised A/D samplingboards interfaced to the commodity PC systems
by using the PCI (peripheral component interconnect) expansion bus (VSSP) and USB2.0 interface(VSSP32). Each A/D sampling board can support
up to four analog inputs; therefore, four boards areused to record signals from 16 full channels of thebaseband converter units for normal geodetic VLBI
observations. On the other hand, the K5/VSI series is realized by high-speed A/D sampler units
and all of the units interface with Linux PC systems with VSI-H speciﬁcations.
To input the data streams from the VSI-H compliant devices, such as the A/D sampler units, a
special board called PC-VSI board was developed.
The board is installed in the PCI-X expansion bus
slot in a PC running Linux, and it can support
high-speed data transfer and recording up to 2
Gbps with each board. By using two PC systems
running Linux, each equipped with a PC-VSI board
and a RAID controller board, a K5/VSI recording terminal can be conﬁgured. Since the K5/VSI
recording terminal can record data streams input
through a VSI data port, it is considered to be a
DTS unit with only DIM capabilities. One K5/VSI
recording terminal consists of two rack-mounted
Linux operating PC units and necessary auxiliarycomponents like an LCD (liquid crystal display)
display, a keyboard, a mouse, and a switch for thecomponents. Each PC unit is installed with a PCVSI board and a RAID controller board on its PCIX expansion bus slot. Sixteen 1 TB hard disks
were connected to and controlled by each RAID
controller board to conﬁgure the RAID-0 system.
For one recording terminal, 32 TB of total data capacity was realized, and the data can be recorded

IVS NICT-TDC News No.33

42

Figure 4. Evolutions of the VLBI Systems from K3 to K5.
at a maximum data rate of 4.096 Gbps by using two VSI-H data input ports. If the data arerecorded continuously, the total capacity can support recordings for up to 17.36 hours. The capacity
is considered suﬃcient for normal VLBI observations spanning 24 hours since the actual recording
time is roughly 50% to 70% the total time for regular VLBI sessions. The capacity of the recording
terminal can also be enlarged by replacing the harddisk units. Since the RAID controller board is used
in a Linux PC environment, the data ﬁles can beeasily accessed from application programs as simple data ﬁles on the Linux operating system.

are some key concepts which identify these systems.
The concept of the K5 VLBI System is to utilize
commodity systems and realize ﬂexible data acquisition and data analysis. As the results, it became
possible to adapt new developments into the existing systems and the it may not be necessary toconsidering the new concepts for next VLBI systemwith the codename of K6. However, it may also
be adequate to launching a new project to develop
new VLBI system since we need to design a newobserving systems to realize VLBI2010. Obviously,
we need to combine various eﬀorts of multiple institutes since the requirements of the VLBI2010
system are all challenging. We need extremely
5. Considerations for the new K6 VLBI high speed AD sampling, high volume data recordSysteming, high speed real-time ﬁltering, high speed data
As it is schematically shown in the Figure 4, transfer and correlation processing. Therefore, if
K3, K4, and K5 VLBI systems were developed at we consider about the K6 VLBI System, its conKashima Space Research Center roughly about ev- cept will be to realize VLBI2010 system. Members
ery 10 years. These three systems have diﬀerent of GSI started to develop high speed data acquiconcepts and characteristics as tabulated in the Ta- sition system under the codename of K6/iDAS. It
will have an ample capability to realize VLBI2010
ble 1.
There were transition period between the sys- observations. In course of the various developments
tems and sometimes the various systems were used for VLBI2010, NICT, GSI, and other institutes will
together. For example, the ADS1000 sampler unit cooperate together to develop missing and unprecehas been used with the GBR1000 K4 recorder unit dented components under the codename of the K6
and K5/VSI PC recorder unit combined with the VLBI system.
PC-VSI interface boards. Therefore, it may not
be meaningful to categorize the individual systems References
into the K3, K4, and K5 categories. However, thereSeptember 2013

43

Table 1. Comparisons of K3, K4, and K5 VLBI Systems.
Development Period
Hydrogen Maser
Phase-cal & Delay-cal
A/D sampler & Recorder
Correlator
Data Analysis
Key Concepts

K3
1979∼


∼56 Mbps
HardwareInternational
Compatibility

K4
1989∼


∼1024 Mbps
Hardware
Automation
Real-time

K5
2000∼
—
—
∼4096 Mbps
Software
Commodity
Versatility

Kiuchi, H., Imae, M., Kondo, T., Sekido, M., Koyama, Y., T. Kondo, M. Sekido, J. Nakajima,
Hama, S. Hoshino, T., Uose, H., and YaM. Kimura and H. Takeuchi, Adaption of themamoto, T., Real-time VLBI system using
VLBI Standard Interface to the K5 VLBI SysATM network, IEEE Trans. Geosci. Remotetem, J. Geod. Soc. Jpn., pp.249-258, Vol.54
Sensing, Vol.38, No.3, pp.1290-1297 (2000)
No.4 (2008)
Kondo, T., Kurihara, N., Koyama, Y., Sekido, M., Kunimori, H., F. Takahashi, M. Imae, Y. Sugand Ichikawa, R., Evaluation of repeatabilimoto, T. Yoshino, T. Kondo, K. Heki,
ity of baseline lengths in the VLBI network
S. Hama, Y. Takahashi, H. Takaba, H. Kiaround the Tokyo metropolitan area, Geouchi, J. Amagai, N. Kurihara, H. Kuroiwa,
phys. Res. Let., Vol.25, No.7, pp.1047-1050
A. Kaneko, Y. Koyama, and K. Yoshimura,(1998)
Contributions and Activities of CommunicaKondo, T., Y. Koyama, J. Nakajima, M. Sekido,
tions Research Laboratory under the Cooperand H. Osaki, Internet VLBI system based onation with Crustal Dynamics Project, in Conthe PC-VSSP (IP-VLBI) board, New Techtributions of Space Geodesy to Geodynamics:
nologies in VLBI, ASP Conference Series, 306,
Technology, eds. D. E. Smith and D. L. Tur205-216 (2003)
cotte, American Geophysical Union GeodyKondo, T., Y. Koyama, R. Ichikawa, M. Sekido,
namics Series, Vol.25, pp.65-79 (1993)
E. Kawai and M. Kimura, Development of Nakajima, J., Koyama, Y., Sekido, M., Kurithe K5/VSSP System, J. Geod. Soc. Jpn.,
hara, N., Kondo, T., Kimura, M., andpp.233-248, Vol.54, No.4 (2008)
Kawaguchi, N.: 1-Gbps VLBI, The ﬁrst deKoyama, Y., Kurihara, N., Kondo, T., Sekido, M.,tection of fringes, Experimental Astronomy,
Takahashi, Y., Kiuchi, H., and Heki, K., AuVol.11, pp.57-69 (2001)
tomated geodetic Very Long Baseline Interferometry observation and data analysis system,
Earth, Planets, and Space, Vol.50, pp.709-722(1998)IVS NICT-TDC News No.33

44

Development of the Software
Polarization
Spectrometer“PolariS”
Izumi Mizuno1,2 (k7330312@kadai.jp), Seiji
Kameno3 , Makoto Kuro1,4 , Amane Kano1 ,Fumitaka Nakamura5 , Noriyuki
Kawaguchi5 , Yoshiaki Hagiwara5 ,Katsunori Shibata3 , Nario Kuno2 , Ryohei
Kawabe3 , Shuro Takano2 , Daisuke Iono5 ,Seisuke Kuji6
1

Graduate School of Science and Engineering,Kagoshima University,1-21-35 Korimoto,Kagoshima, Kagoshima 890-0065
2
Nobeyama Radio Observatory, Minamimaki,
Minamisaku, Nagano, 384-1305, Japan
2
Joint ALMA Observatory, Alonso de Cordova
3107 OFC 129, Vitacura, Chile
4
Shoyo High School, Tatemachi, Hachioji, Tokyo
193-0944, Japan
5
National Astronomical Observatory of Japan,
Mitaka, Tokyo 181-8588, Japan
6
Mizusawa VLBI Observatory, 2-12
Hoshigaoka-cho, Mizusawa, Oshu, Iwate
023-0861, Japan
Abstract: We report the development of the softwarebased polarization spectrometer, PolariS, whichaims the ﬁrst detection of the Zeeman eﬀect of the
CCS emission line to measure the magnetic ﬁeld instar-forming cores. This report addresses the speciﬁcation, design, and performance of the PolariS in
the commissioning phase.
1.

Introduction

Polarization spectrometer is a device to measure
spectra in full Stokes components of I, Q, U, andV . Stokes parameters in radio astronomy are essential to address magnetic ﬁelds in the emission
region or along the propagation path. For example, the Zeeman eﬀect is a key phenomenon to measure magnetic ﬁeld strength directly. An emission
line under a magnetic ﬁeld shows frequency-shifted
proﬁles due to energy level splitting. The Zeeman
shift is proportional to the line-of-site magnetic
ﬁeld strength and opposite between two circularpolarizations (LHCP and RHCP). Thus, Stokes V
spectrum of the emission line is a concrete measureof the magnetic ﬁeld strength.
The Zeeman eﬀect of the CCS molecule is an important sensor for magnetic ﬁelds in star-forming
cores. The emission line of JN = 43 − 32 transition

Figure 1. Schematic diagram of the PolariS and thereceiving system of Z45 at the NRO 45-m telescopeat 45.379 GHz is strong (Ta ∼ 2 K), narrow (∼ 0.5
km s−1 ) and exhibit relatively large Zeeman splitting of 6.3 × 105 Hz G−1 [3]. In spite of some trials,
however, no successful detection on CCS has beenreported because of diﬃculties in measuring tiny
Zeeman splitting in Stokes V .
We aim the ﬁrst detection using the Nobeyama 45m radio telescope which oﬀeres the largest aperture at this frequency. We have developed a polarization spectrometer, “PolariS”, together with adual-polarization receiver for this purpose. In thispaper we report the design of the PolariS and commissioning results.
2.

Speciﬁcations and Design

For the purpose of CCS Zeeman observations, we
set the technical requirements:• Input : dual linearly polarized analog signal
streams• Output : Full Stokes (I, Q, U, V ) spectra• Bandwidth : 8 MHz to cover 50 km s−1• Resolution : 61 Hz for Zeeman shift of 100 μG• Cost : < JPY 2, 000, 000
To meet the requirements, we designed a softwarebased spectrometer, PolariS. Figure 1 shows theschematic diagram of the PolariS. The input 4 IF
signals are digitized with the K5/VSSP32 VLBI
sampler[1] at 64 Msps 8-bit quantization. Digital ﬁltering and level clipping is applied to output
4 data streams with each 16 Msps (8-MHz bandwidth) 4-bit quantization. The data streams aresent to the PolariS computer via USB 2.0 interface
and processed for FFT (Fast Fourier Transform)and cross production in the GPU (Graphics Processing Unit) utilizing the CUDA (Compute Uniﬁed Device Architecture) library to output (cross)power spectra. The power spectra are accumulated
for relevant period (typically 1 sec) and recorded in
the storage. The operation software is open in the
GitHub1 .
1 https://github.com/kamenoseiji/PolariS

September 2013

45

Figure 2. The front-inside view of the PolariS computer
We have four correlation pairs of XX ∗ , XY ∗ ,Y X ∗ , and Y Y ∗ through the process, where X
and Y stand for orthogonal linear polarizations, respectively. Each correlation pair contains 131072
spectral channels to oﬀer the 61-Hz resolution.
These pairs are related to the Stokes parameters:
⎛
⎞
⎛
⎞
⎞⎛
I
1 0
0
1
XX ∗
⎜ Q ⎟ 1 ⎜ c −s −s −c ⎟ ⎜ XY ∗ ⎟
⎜
⎟,
⎜
⎟
⎟⎜
⎝ U ⎠= 2⎝ s c
c −s ⎠ ⎝ Y X ∗ ⎠Y Y ∗
V0 −ii0where c = cos 2ψm , s = sin 2ψm , and ψm is theparallactic angle. This conversion is employed inoﬀ-line reduction softwares.
Figure 2 shows the main body of the PolariS computer installed in the NRO. The computer costs
JPY 70, 000 for the main body with the NVIDIA
GT640 graphic card and operates on the Ubuntu
12.04 LTS. The total cost is JPY 600,000 including
the ACD.

Figure 4. (Top) Line strength measured by the PolariS as a function of input power. (Bottom) Departure from the linear trend. Horizontal lines indicate the ±1% error range.
3.

Commissioning Veriﬁcation

We have tested the performance of the PolariS on
the aspects: (1) spectral resolution, (2) linearity,(3) sensitivity, (4) stability, and (5) cross correlation capabilities. We used the Z45[2] and H22
receivers, working at 45 and 22 GHz, respectively,
installed on the NRO 45-m telescope.
3.1

Spectral Resolution Function

Since the PolariS is a FX-type spectrometer witha triangular weighting function in an FFT segmentof 262144 samples, we expect a Sinc-squared spectral resolution function with the FWHM of 54.07
Hz. To test the resolution, we prepared the baseband continuum signal from the Z45 receiver andinjected a monochromatic signal at 68 MHz generated by the signal generator (Agilent E82579). The
frequency was swept over the range of 400 Hz by
a 4-Hz step. Figure 3 shows the measured resolution function, which follows Sinc2 function with the
FWHM of 54.02 Hz and consistent with the design.
Figure 3. The spectral resolution of the PolariS.
Measurements (dots) and best-ﬁt Sinc2 curve with
the FWHM of 54.02 Hz (solid line) are displayed.

3.2

Linearity

To verify the linearity in terms of spectral line intensity, we used the same conﬁguration with subsection 3.1 and changed the power of the injection
signal over the range of 41 dB by a 1-dB step.

IVS NICT-TDC News No.33

46

Figure 4 shows that the departure from the linear
trend is less than 1% in the range of 13 dB except
a few outliers.

Figure 5. The standard deviation of the spectrum
as a function of integration time.

3.3

Sensitivity

To evaluate the sensitivity, i.e. the standard deviation, σ, of the spectrum as a function of integration
time, τ , we conducted spectroscopy of the Z45 signal under the shutter-closed circumstance. Figure
5 shows the results that well coincide to the ideal
curve of σ ∝ τ −1/2 .
Figure 6. (Top) Spectral Allan variance of 2392s integrated spectrum. The bandpass shape is ﬂat
3.4 Stability
until the ﬁrst bottom of 7643 ch. (Bottom) TimeUsing a long-term (2392 s) spectroscopy under the base Allan Variance together with the ideal curvecondition in subsection 3.3, we evaluated the ﬂat- in the solid line. The stability time exceeds 1000 s.
ness of the bandpass shape by taking the spectral
Allan variance [4] and stability by the time-based measured as 97.6 ± 0.18% and the phase was staAllan variance. As shown in Figure 6, the band- ble with the standard deviation of phase was 3◦ .36
pass shape is ﬂat for the channel separation of 7643 during the 100-s observation.
ch and stable over the time period of 1000 s.
4. Summary
3.5 Cross Correlation
Throughout the commissioning, we have veriﬁed
To verify the cross correlation capability between the basic performance of the PolariS met the techorthogonal polarizations, we injected a linearly po- nical requirements for CCS Zeeman observations,larized wave from the calibration port of the H22 in terms of spectral resolution, sensitivity, stability,
receiver which receives dual circular polarizations.
and cross correlation capabilities. Since PolariS is a
The wave is generated by the signal generator (Agsoftware-based equipment using commodity prodilent 83650L) and transmitted with a transducer
ucts, the radio astronomy community can easily
with a rectangular waveguide. Thus, we expect
install and utilize it or can contribute to improve100% correlation with a constant relative phase forments on specialized speciﬁcations.
the ideal case. We show the results in Figure 7.
The average of the cross correlation amplitude wasSeptember 2013

47

Acknowledgement
This project is ﬁnancially supported by the joint
development research program of the National Astronomical Observatory of Japan. The Z45 receiver
is developed through the Grants-in-Aid for Scientiﬁc Research Program 24244017.
References[1] Kondo, T., Koyama, Y., Takeuchi, H., &Kimura M. 2006, Proceedings of the IVS 2006
General Meeting, 195[2] Kozu, M. et al. 2012, Annual Meeting of the
Astronomical Aociety of Japan, V106b.
[3] Shinnaga, H., & Yamamoto, S. 2000, ApJ,
544, 330[4] Yamaki, H., Kameno, S., Beppu, H., Mizuno,
I., & Imai, H. 2012, PASJ, 64, 118

Figure 7. (Top) Correlation amplitude and (Bottom) phase across the elapsed time.

48

IVS NICT-TDC News No.33∼ News ∼ News ∼ News ∼ News ∼ News ∼ News ∼ News ∼ News ∼ News ∼ News ∼Restoration of 34m Antenna Azimuthal Wheel/Rail from theDamage of the Earthquake 2011
Kashima area was suﬀered from the “2011 Tohoku Megaquake”[1]. The damage to the 34m antenna wasinitially thought to be not so hard, although a large crack on the running surface of the azimuthal wheel
has been found in the later inspection. Then detailed inspection was made by the original manufacturer
General Dynamics SATCOM Technologies (originally ’TIW’) in May 2012. Four azimuthal wheels and
16 wear-strip plates (Azimuthal rail) were replaced with new ones by the end of March 2013. Precision of
the installation of azimuthal wear-strip plates was 0.1 mm height over the whole 20 m diameter azimuth
rail circle. The installation of azimuthal wheel was performed with axis alignment at 10−6 radians ofprecision to the center of the azimuthal circle. Fig. 1 shows pictures of the damage on the azimuthal
wheel surface and installation of a new wheel. Now, Kashima-34m VLBI station has been fully restoredfrom the damage of the earthquake. It has started participation to the international IVS sessions anddomestic VLBI sessions. Moreover, this antenna will become one of the keys in the Gala-V project[2],which is the mission of VLBI group at NICT/Kashima.

Figure 1. Left panel shows the crack on the wheel with 20cm/7.5cm size. Right panel indicates theinstallation of new wheel, whose axis is accurately aligned to the center of the azimuthal axis by using atelescope.

References[1] Ichikawa Ryuichi, Preface, IVS NICT-TDC News, No. 32, pp.1–4, 2013.
[2] Mamoru Sekido, et al., Development of Wide-band VLBI system (Gala-V), IVS NICT-TDC News,No. 33, pp.11–14, 2013.
(Mamoru Sekido, Eiji Kawai/NICT Kashima)

“IVS NICT Technology Development Center News” (IVS NICT-TDC News) published by the
National Institute of Information and Communications Technology (NICT) (former the Communications Research Laboratory (CRL)) is the continuation of “IVS CRL Technology Development
Center News” (IVS CRL-TDC News). (On April 1, 2004, Communications Research Laboratory(CRL) and Telecommunications Advancement Organization of JAPAN (TAO) were reorganized
as “National Institute of Information and Communications Technology (NICT)”.)
VLBI Technology Development Center (TDC) at NICT is supposed
1) to develop new observation techniques and new systems for advanced Earth’s rotation observations by VLBI and other space techniques,2) to promote research in Earth rotation using VLBI,
3) to distribute new VLBI technology,4) to contribute the standardization of VLBI interface, and5) to deploy the real-time VLBI technique.
The NICT TDC newsletter (IVS NICT-TDC News) is published annually by NICT.

This news was edited by Mamoru SEKIDO, Kashima Space Technology Center. Inquires on thisissue should be addressed to Mamoru SEKIDO, Kashima Space Technology Center, National
Institute of Information and Communications Technology, 893-1 Hirai, Kashima, Ibaraki 3148501, Japan, e-mail : sekido@nict.go.jp.
Summaries of VLBI and related activities at the National Institute of Information and Communications Technology are on the Web. The URL to view the home page of the Radio Astronomy
Applications Section of the Space-Time Measurement Group of Space-Time Standards Laboratory is : “http://www2.nict.go.jp/aeri/sts/stmg/index e.html”.

IVS NICT TECHNOLOGY DEVELOPMENT CENTER NEWS No.33, September 2013
International VLBI Service for Geodesy and Astrometry
NICT Technology Development Center News
published by
National Institute of Information and Communications Technology, 4-2-1 Nukui-kita, Koganei,
Tokyo 184-8795, Japan