ISSN 1882-3432

CONTENTS
Proceedings of the 15th NICT TDC Symposium (Kashima, June 30, 2016)
Detection of TEC Anomalies by Using Correlation Analysis -2011 Tohoku- . . . . . . 1
Oki caseTakuya Iwata and Ken Umeno
Water Vapor Radiometer: Challenge Again...... 4

Noriyuki Kawaguchi
Status on the Ishioka Geodetic Observing Station
Masayoshi Ishimoto, Michiko Umei, Takahiro Wakasugi, Ryoji Kawabata,
Tomoo Toyoda, Basara Miyahara, and Yoshihiro Fukuzaki...... 9

Development of Wideband Antenna. . . . . 13

Hideki Ujihara
Development Status of GALA-V Broadband VLBI – Geodetic Solution and . . . . . 14
Clock Comparison –M. Sekido, K. Takefuji, H. Ujihara, T. Kondo, Y. Miyauchi, M. Tsutsumi,
E. Kawai, S. Hasegawa, J. Komuro, R. Ichikawa, Y. Koyama, Y. Hanado,
K. Terada, K. Namba, R. Takahashi, T. Aoki, T. Ikeda, R. Kawabata,
M. Ishimoto, T. Wakasugi, Y. Umei, T. Toyoda, K. Watabe, and T. Suzuyama
Performance of Direct Sampler K6/GALAS. . . . . 20

Kazuhiro Takefuji
VERICA, A New Verification Method of Applied Calibrations onto Visibility . . . . . 23
Data (II)
Makoto Miyoshi
VLBI Direct Sampling Digital Frontend
Kenichi Harada, Yoshinori Hayashi, Kenji Ema, Yuichi Chikahiro,
Hirofumi Onuki, and Kensuke Ozeki. . . . . 26

November 20161

Detection of TEC Anomalies 2. Analysis method
by Using Correlation Analysis STEP 0. Choose the central GNSS station andset up three parameters, i.e. tsample , ttest , and-2011 Tohoku-Oki caseM. t
is the length of data used for regressample

Takuya Iwata(iwata.takuya.37m@st.kyoto-u.ac.jp),
Ken Umeno , Department of Applied
Mathematics and Physics, Graduate school ofInformatics, Kyoto University,
Yoshidahon-machi, Sakyo-ku, Kyoto, Japansion training and ttest is the length of data used
for regression test, and the value M denotes thenumber of GNSS stations we use.
STEP 1. At each station i and at each time epocht, let SampleData be the data from t to t + tsample
and T estData be the data from t + tsample tot + tsample + ttest .
STEP 2. Fit a curve to SampleData by the leastsquare method.
STEP 3. Calculate a deviation of the T estDatafrom the model curve, representing as an”anomaly”. The anomaly at station i at time t
is denoted as xi,t .
STEP 4. Calculate a summation of correlations
between the anomalies at the central GNSS station and the surrounding stations as follows:

Abstract: Ionosphere contains large amount of electrons and signals sent by GPS (Global Positioning System) and other GNSS (Global Navigation
Satellite System) satellites are aﬀected by theseelectrons. We can observe daily changes of Total Electron Content (TEC) in ionosphere by using the phase diﬀerences between the two carrier waves from GNSS satellites. In recent research, some papers show the presence of the preseismic TEC anomalies which can be seen before
large earthquakes in the world [2, 3, 4]. However,these analysis methods have some problems whichcause arguments among the related researchers[5, 6, 7]. In this research, we propose an analysis
method which can detect TEC anomalies before
large earthquakes. Our method adopted the correlation analysis (also used in VLBI analysis) to
reduce noises on TEC data. As a result, our proposed method detected TEC anomalies about one
hour before 2011 Tohoku-Oki earthquake, whichis the largest earthquake in Japan during recent
years. As further research, we will check otherlarge earthquakes and establish a robust method
to detect TEC anomalies before earthquakes.

Here, N is the number of data in TestData, Δt is asampling interval in TestData, which means Δt =ttest /(N − 1), and i = 0 means the central GNSS
station, where tsample = 2.0 [hours], ttest = 0.25
[hours] and M = 30 [stations].
We can choose arbitrary functions as a ﬁtting
curve in STEP 2. In this research, we adopted 7th
polynomial functions.

1.

3.

Introduction

Japan has a dense GNSS observation network(GNSS Earth Observation NETwork, GEONET)to correct and analyze the large amount of GNSS
observation data. These GNSS data (in recent
a few years) are open to public and anyone
can download and analyze freely via the Internet(terras.gsi.go.jp).
TEC data analysis is one of the major researches
using GNSS. In particular, analyzing TEC data before large earthquakes has been drawn considerable
attention.
In this research, we analyzed TEC data before
the 2011 Tohoku-Oki earthquake data, which isalso freely available from GEONET.

C(T ) =
M N
−1


1
xi,t+tsample +jΔt x0,t+tsample +jΔt
N × M i=1 j=0(1)
T = t + tsample + ttest

2011 Tohoku-Oki earthquake

The 2011 March 11 (05:46 UT) Tohoku-Oki
earthquake occurred at the northeast Japan. Its
magnitude is huge (Mw 9.0) and the earthquake
caused great damage to this area and all overJapan. This earthquake is the largest earthquake
during the period that the GNSS data are freely
available from GEONET.
Figure 1 shows the location of the epicenter andthe SIP (Sub Ionospheric Point) track of the 26
GPS satellite and the 0214 (Kitaibaraki) GNSS receiver. The intersection of the line-of-sight andionosphere is called as IPP (Ionospheric Pierce
Point) and SIP is its projection to the ground.
4.

Results

Figure 2 shows the result of the correlation analysis on March 11, 2011. We chose the GPS satellite

IVS NICT-TDC News No.36

2

2011/03/11
Central Station ID: 0214

SIP
C(t)

20

epicenter
0214

10

0
Mainshock

04:30

05:00

05:30

06:00

06:30

time

Figure 1. The location of the epicenter of the 2011
Tohoku-Oki earthquake and the SIP track of the
GPS satellite 26 and the 0214 receiver. The boldblack circle indicates the location of SIP when theearthquake occured.
26 and the 0214 (Kitaibaraki) station as a centerstation. The x-axis is time (UT) and the y-axis is
the correlation values deﬁned in eq. (1). The black
vertical line in the ﬁgure shows the earthquake occurrence time (05:46 UT). As time approaches theearthquake occurrence time, the correlation value(C(t)) is becoming large. Furthermore, the correlation value looks the characteristic wave-like pattern.
Figure 3 shows the results of the correlation
analysis on non-earthquake days, namely, 10 days,
20days, 30days and 40 days before the earthquake.
Comparing Fig. 2 with Fig. 3, we can conﬁrm
that the correlation values on the earthquake day
are much larger than that on the non-earthquakedays. The correlation values on non-earthquake
days are at most 5, however, the correlation values
on earthquake day are over 20 before the earthquake.
Figure 4 shows the results of the correlation analysis of all the GNSS stations in GEONET before the main shock. The red area in the ﬁguremeans the TEC-anomalous region and the yellow
area means the clam (not anomalous) region. The
anomalous area can be seen near the epicenter as
the earthquake occurrence time (05:46 UT) is closing.
While the physical mechanisms responsible for
the TEC anomalies before the earthquake are notso clear up to now, some physical models which
explain it have been proposed. One of the models
is based on the laboratory experimental results ofstressed rock [8, 9]. According to the experimental
results, as rock are subject to stress, they produce

Figure 2. The result of correlation analysis on
the March 11, 2011. We used the TEC data derived from the pair of the GPS satellite 26 and the0214 GNSS station (and 30 stations surroundingit) to calculate correlation values. The x-axis istime (UT) and the y-axis is the correlation values
deﬁned in eq. (1). The black vertical line is theearthquake occurrence time (05:46 UT).
positive holes at the surface of the rock. Hence, theelectric ﬁelds are generated in the air and aﬀect theionosphere. A lithosphere-atmosphere-ionosphere
coupling model based on the experimental results
is proposed and improved in recent studies [10, 11].
This model can explain the mechanisms of TEC
anomalies before large earthquakes [12].
5.

Summary

In this research, we proposed the correlation
analysis for detecting TEC anomalies. This analysis method is familiar to Informatics and radio
astronomy, but has not been applied to analyzing
TEC data. In the 2011 Tohoku-Oki earthquake
case, the TEC anomaly near the epicenter is detected about one hour before the main shock by
the correlation analysis. This anomalous TEC values have a characteristic pattern, but the physicalmechanism responsible for it is still unclear. As further research, other large earthquakes should be investigated to conﬁrm the presence of TEC anomalies before large earthquakes. Furthermore, it isanticipated that the physical mechanisms which reveal the relationship between the seismic activities
and ionospheric disturbances are explored.
References[1] Iwata, T. and K. Umeno, Correlation analysis for pre-seismic total electron content
anomalies around the 2011 Tohoku-Oki earth-November 20163
2011/02/09

2011/01/30

04:45−5.000 − −1.250− 2.500− 6.250− 10.000− 13.750− 17.500− 21.250− 25.000

40

10

08:30

09:00

06:30

09:30

07:00

07:30

08:00

time

time

2011/02/19

2011/03/01

08:30

30

20

20

30

08:00

35

Latitude

07:30

35

07:00

−5.000 − −1.250− 2.500− 6.250− 10.000− 13.750− 17.500− 21.250− 25.000

Latitude

0

0

05:21

40

45

C(t)

C(t)

10

45

20

20

130

135

140

145

130

135

0

06:00

06:30

07:00

08:00

05:00

05:30

06:00

06:30

07:00

time

140

145

45

05:42
−5.000 − −1.250− 2.500− 6.250− 10.000− 13.750− 17.500− 21.250− 25.000

35
30

30

Figure 3. The results of correlation analysis on
non-earthquake days (10 days, 20 days, 30 days
and 40 days before the earthquake). We used samethe GPS satellite and the GNSS stations as Fig. 2.

35

Latitude

time

07:30

−5.000 − −1.250− 2.500− 6.250− 10.000− 13.750− 17.500− 21.250− 25.000
Latitude

05:30

05:39

40

0

145

10

45

10

140
Longitude

40

C(t)

C(t)

Longitude

130

135

140
Longitude

145

130

135
Longitude

quake, J. Geophys. Res. Space Phys., 121, doi:
10.1002/2016JA023036., 2016.
Figure 4. The results of correlation analysis of all[2] Heki, K., Ionospheric electron enhancement the GNSS stations in Japan on the earthquake day.
preceding the 2011 Tohoku-Oki earthquake, We used same the GPS satellite 26. The black sign
Geophys. Res. Lett., Vol. 38, L17312, 2011.
is the epicenter. The earthquake occurrence time is
05:46 [UT].
[3] Heki, K. and Y. Enomoto, Preseismic ionospheric electron enhancements revisited, J.
Geophys. Res. Space Phys., vol. 118, pp. 6618– [8] Freund, F., Toward a uniﬁed solid state the6626, 2013.
ory for pre-earthquake signals, Acta Geophys.,vol. 58, No. 5, pp. 719–866, 2010.
[4] Heki, K. and Y. Enomoto, Mw dependence ofpreseismic ionospheric electron enhancements, [9] Freund, F., Earthquake forewarning – A multidisciplinary challenge from the ground up to
J. Geophys. Res. Space Phys., vol. 120, pp.
space, Acta Geophys., vol. 61, No. 4, pp. 775–
7006–7020, 2015.
807, 2013.
[5] Kamogawa, M. and Y. kakinami, Is an ionospheric electron enhancement preceding the [10] Kuo, C. L., J. D. Huba, G. Joyce and L. C.
Lee, Ionosphere plasma bubbles and density
2011 Tohoku-oki earthquake a precursor?, J.
variations induced by pre-earthquake rock curGeophys. Res. Space Phys., vol. 118, No. 4,
rents and associated surface charges, J. Geopp. 1751–1754, 2011.
phys. Res., vol. 116, A10317, 2011.
[6] Utada, H. and H. Shimizu, Comment on ’Preseismic ionospheric electron enhancements re- [11] Kuo, C. L., L. C. Lee and J. D. Huba, An
improved coupling model for the lithospherevisited’ by K. Heki and Y. Enomoto, J. Geoatmosphere-ionosphere system, J. Geophys.
phys. Res. Space Phys., vol. 119, no. 7, pp.
Res. Space Phys., vol. 119, pp. 3189–3205,
6011–6015, 2011.
2014.
[7] Maci, F., J. N. Thomas, F. Villani, J. A. Secanand N. Rivera, On the onset of ionospheric [12] Kuo, C. L., L. C. Lee and K. Heki, Preseismic TEC changes for Tohoku-Oki earthquake:precursors 40 min before strong earthquakes,
Comparisons between simulations and obserJ. Geophys. Res. Space Phys., vol. 120, No. 2,
vations, Terr. Atmos. Ocean. Sci., vol. 26, pp.
pp. 1383–1393, 2015.
63–72, 2015.

IVS NICT-TDC News No.36

4

Water Vapor Radiometer:
Challenge Again
Noriyuki Kawaguchi (kawagu.nori@nao.ac.jp),
Visiting Professor, Shanghai Observatory
Professor Emeritus, National Astronomical
Observatory,
Eldia 1507, 1-29-1 Tamagawa, Chofu, Tokyo,
182-0025 Japan
Abstract: In 1984, a VLBI group in Kashima
Branch, Radio Research laboratory (at present
Kashima Space Technology Center of NICT, National Institute of Information and Communications Technology) tried to develop a water vapor
radiometer, WVR, which aims at obtaining better accuracy in geodetic VLBI observations. With
the WVR data they did not get remarkable improvements on geodetic solutions for the US-Japan
joint VLBI program. Since then the developmentof WVR has been inactive in Japan until the KEK,High Energy Accelerator Research Organization in
Japan) succeeded to measure the wideband spectrum of a resonance pattern of a water vapor
molecule in the atmosphere in 2015. The successinspires developments of a new advanced WVR in
Japan.
Here I will review the current state of developments on the WVR in the world and give suggestions on the new WVR in future.

Figure 1. K3 WVR developed by Kashima in theﬁrst trial

Figure 2. Wideband water vapor emission spectrum
detected by KEK WVR

current state of the WVR developed and operated
in the world is overviewed. In Section 3, a serious
In 1985 a Water Vapor Radiometer, WVR, was problem on the WVR happened at a bad weather
developed by a VLBI group in Kashima Branch, condition of a thick cloud and heavy raining is disRadio Research laboratory (at present Kashima cussed. In section 4, a new WVR design on a wide
Space Technology Center of NICT, National In- band spectrometer with a high speed AD converter
stitute of Information and Communications Tech- is proposed.
nology), which aims at obtaining better accuracy
on geodetic solutions on the Joint US-Japan VLBI 2. WVRs in the world
program (see Fig.1). With the WVR data, howThe Onsala Space Observatory has been workever, they could not get remarkable improvementsing
on the WVR (Forkman 2003)[1] which is shownon the geodetic solution. Since then no trial on
the WVR developments has been made in Japan in Fig.3. At a time when the receiver is in the
except for a trial test of a water vapor spectrom- calibration cycle, the mirror switches the beam toeter attached on a 10-m radio antenna located at sky and a hot load behind the mirror alternatively.
the Usuda Deep Space Center. The work is per- This calibration method is now widely employed toformed by Yoshiharu Asaki in 2005 but not ap- current WVRs for calibrating power measurements
plied to actual VLBI observations. In 2015, the to sky noise temperature.
The JPL developed a new advanced WVR to corKEK, High Energy Accelerator Research Organirect
the wet path delay for deep space navigation
zation in Japan has succeeded to measure the wide(Tanner2003)[2]. It is a highly stable radiometerband spectrum of a resonance pattern caused by awater vapor molecule in the atmosphere as shown designed carefully to keep environment temperature in the receiver box within 0.004 degree (seein Fig.2.
to getThe success inspires developments of a new ad- Fig.4). The temperature stability is a key[3](4][5]. Inhighstability
in
sky
noise
measurements
vanced WVR in Japan. In the next section the1.

Introduction

November 2016

5

Figure 3. The Onsala WVR[1]Figure 5. The mm accuracy of WVR excess pathdemonstrated with VLBI [6]work with a high frequency VLBI at 22 and 43 GHz
to be done with the 65m telescope. The WVR is
expected to use in the correction of the atmosphericphase ﬂuctuation in order to get a long coherencetime and to make the sky absorption correction as
well.

Figure 6. The WVR at the Tianma 65-m site ofShanghai Astronomical Observatory, China

Figure 4. A hgihly temperature stabilized receiverof the JPL AWVR
the sky noise measurement, noise temperature andgain of a receiver shall be kept constant together
with physical temperature of the hot load, otherwise the sky noise originated in the water vapor
emission in the sky is measured wrong.
Tahmoush & Rogers (2000)[6] shows good agreement on the wet delay less than 1 millimeter between the WVR delay and the VLBI delay as shownin Fig. 5.
Shanghai Astronomical Observatory operates a
WVR at the Sheshan site nearby the Tianma 65m.
The similar radiometers are prepared for all four
VLBI stations in Chinese VLBI Network (CVN),
Shanghai, Beijing, Urumuqi and Kunmin. Fig. 6
show the WVR located at the Tianma 65msite,which was ﬁrst introduced in 2013 and expected to

The WVR receives sky noise emission in dual
frequency channels, 23.8 and 31.4 GHz, each bandwidth of which is 500MHz. It has an absorber forthe hot load calibration at the bottom of the receiver cabin. From the sky noise measurements on
the dual frequency channels, it produces the EPL,
Excess Path Length, in the unit of millimeter. The
result will be shown in the next section.
IRAM WVRs have three receiving channels asshown in Fig. 7 and were used to correct interferometer phase as shown in Fig. 8 (Bermer(2010)[7]).
The university of Bern developed a WVR shownin Fig. 9 (Bleisch(2011)[8]. The WVR has an
unique calibration system of a hot bar which partially cover the beam toward the sky.
A sensitive narrow band spectrometer succeeded to detect water vapor in the stratosphere(Kämpfer(2003))[9]. The spectral is so sharp in thefeature due to the extremely low pressure that thehigh resolution spectrometer is a key of the detection together with high sensitivity. The detectionof the sharp spectrum clearly show the existence ofwater vapor in the stratosphere higher than 10km

IVS NICT-TDC News No.36

6

Figure 7. Three-channel radiometer developed by
IRAM

Figure 8. Interferometer phase corrected by WVR
above ground.
A WVR is working in Korea for the studies of
middle atmosphere (DeWachter(2011))[10] in Sookmyung Women’s University. The WVR is the same
design as that of University of Bern.
3.

Bad responses under cloud and rain

In Fig.12 the excess path lengths measured by
SHAO WVR in comparison with GPS zenith delay
and that derived with the Ray Trace method areshown on the day of May 31, 2016. At the CSTtime around 8h, the thick cloud covered the sky andat around 18h a heavy raining started. Under these

Figure 9. WVR developed by University of Bern,
Switzerland

Figure 10. Water vapor in stratosphere, no pressure broadening spectrum[9]Figure 11. The WVR working in the Sookmyung
Woman’s University in Korea
bad weather conditions the EPL by SHAO WVRshows big errors compared to EPLs measured by
GPS and Ray Trace. The incredibly large EPL ofthe WVR may come from the wrong conversion of
the sky noise temperature onto the EPL. The sky
noise increased with absorption by liquid water ina cloud and a rain is converted to the large EPL
by an error. The imperfect separation of the EPL
from the absorption may cause the large error.
The similar bad result was reported by Jung-ho
Cho(2006)[11] as shown in Fig. 13. They compared
the WVR EPL to the VLBI delay and found good
agreement between them at the start of the day

Figure 12. Excess path length measured by SHAOWVR in comparison with GPS and Ray Trace

November 2016

Figure 13.
raining[11]Measurement error of WVR under

until the mid day but big discrepancy in the latter
half of the day. They noted the discrepancy wascaused by a rain.
Not only a rain but also a heavy cloud causes the
big error in the WVR measurement owing to theimperfect separation of the vapor emission from theliquid water absorption. Both of the water vapor
and the liquid water cause the rise in the sky noise
temperature. We need to note that the liquid water
absorption is almost constant or slightly linearly
proportional to frequencies around the water vapor
resonance peak at 22.2 GHz. We need to separate
the water vapor emission by the resonance spectral
pattern.
The perfect separation between absorption anddelay was reported by Elgerd(1998)[12] with theOnsala WVR as shown in Fig. 14. The upper
plot indicates the delay (EPL) and the lower absorption. The wet delay measured by the WVR is
not aﬀected by large absorption by the rain. Also
we can see the rapid decrease in the wet delay after the rain stop. This is meteorologically understandable that a water vapor in the atmosphereis converted to the liquid water and fall down toa ground which causes the decreases in the water
vapor content in the atmosphere. Even under raining, the WVR shows a reasonable value in the wet
delay. This indicates that the careful analysis on
the water vapor emission proﬁle (resonance patternaround 22.2 GHz) makes possible to separate thewet delay from the liquid water absorption.
4.

Technical points for future developments

7

Figure 14. Separation of the excess path from absorption due to liquid water[12]ature of the sky in Kelvin by an equation, P =kGB(Tsky + Trx), where P is a received power, k is
the Boltzmann constant, G is a receiver gain, B isa receiver bandwidth, Tsky is a sky noise temperature and Trx is a receiver noise temperature. If
the receiver Gain, G, the bandwidth, B and the receiver noise temperature Trx is stable and known,
it is straight forward to convert the power to thesky noise temperature. The gain and the receivernoise temperature are, however susceptible to ambient temperature. This is a reason why we needto carefully keep the temperature of a receiver box.
If we have two reliable references in the brightness
temperature, Tref 1 and Tref 2 , and by putting thesereference temperatures in place of Tsky we can solve
for values of kGB and Trx. Usually we use a hotload and a cold load for two reference brightness
temperatures. The hot load is an absorber in aroom temperature (∼300K) and the cold load isan absorber dipped into a liquid nitrogen (∼80K).
Another way is so called a Y-factor method, inwhich the power ratio is measured. The power raP, where Psky is the power received
tio Y, Y = Psky
hotby the WVR toward the sky and Phot is the power
terminated by the hot load. By taking the ratio,
a common factor of kGB is canceled and we get
hot +Trx
the power ratio of Y as Y = TTsky+Trx , and fromthe power ratio the Tsky is easily reduced by taking Thot known. In advance to this Y-factor measurement, the receiver noise shall be measured by
hot +Trxa hot/cold calibration, Y  = TTcold+Trx where Thot
and Tcold are known. Also it is assumed the Trx isconstant during sky noise measurements. A technical point on this method is a time how long we
can keep the receiver noise temperature constant.
Again it is important to keep the ambient temperature in the receiver box.

By reviewing the current status of world WVRs
and by considering the bad eﬀect by cloud and rain,
4.2
some technical points are described here.
4.1

Radiometer calibration

Spectrum measurement with a highspeed ADThe SHAO WVR measures only two frequency
A radiometer measures the power in dimension channels and has not enough capability to sepaof Watt and converts it to the brightness temper- rate water vapor from liquid water as mentioned inIVS NICT-TDC News No.36

8

Section 3. This is one reason why the WVR sometimes shows outrageous values in the excess path
length. The best way to achieve ideal separation
is to make measurement the frequency spectrum
around the water vapor resonance as shown in Fig.
2. The resonance spectrum is ﬁt to the theoretical
one’s and then the total amount of water vapor in
the air is estimated. From the water vapor content
in the air we can separately deduce the wet delay
and the absorption.
The water vapor spectrum is widely spreading
in frequency over a few GHz around the resonancepeak frequency at 22.2GHz due to the high pressure in the lower atmosphere. Tahmoush(2000)[6]
got the wide band spectrum by sweeping the frequency of a local oscillator in the frequency down
converter. The Fig.2 measured by the KEK WVR
is ﬁgured the spectrum by an analog spectrum analyzer. In both of them it takes a few seconds toa few tens seconds to get a full frequency span of
the water vapor resonance. To correct a short term
variation of the wet path, it is preferred to use ahigh speed AD converter and a digital spectrometer. The new digital water vapor spectrometer is
now under development in Japan with a sampling
frequency of 16GHz on the frequency band spanned
from 16 to 24GHz. The author hope it will eﬀectively work in the wet path correction in delay andabsorption, and is used for precise astrometry andgeodesy, and reliable imaging in radio astronomy.
5.

Acknowledgments

ters for the Australia Telescope Compact Array, Publications of the Astronomical Society of Australia, arXiv:1212.60101v2, 30 April
2013[4] C. Straub, A. Murk, and N. Kämpfer,
MIAWARA-C, a new ground based water vapor radiometer for measurement campaigns,
Atmos. Meas. Tech., 3, 1271–1285, 2010[5] Michael Britcliﬀe, Daniel Hoppe, and ManuelFranco, A Low-Cost Water Vapor Radiometer for Deep Space Network Media Calibration, IPN Progress Report 42-188, February
15, 2012[6] David A. Tahmoush and Alan E. E. Rogers,
Correcting atmospheric path variations in millimeter wavelength very long baseline interferometry using a scanning water vapor spectrometer, Radio Science, Volume 35, Number
5, Pages 1241–1251, September-October 2000
[7] Michael Bremer, Atmospheric Phase Correction, 7th IRAM Millimeter Interferometry
School, Grenoble, October 4-8, 2010[8] R. Bleisch, N. Kämpfer and A. Haefele, Retrieval of tropospheric water vapour by using
spectra of a 22 GHz radiometer, Atmos. Meas.
Tech., 4, 1891–1903, 2011[9] Nikiaus Kämpfer, Beat Deuber, Dietrich Feist,
Daniel Gerber, Christian MCtzler, Lorenz
Martin, June Morland, Vladimir Vasic, Berne,
Microwave Remote Sensing of Water Vapor in
the Atmosphere, Geographica Helvetica Jg. 58
2003

The author would like to thank to Dr. M. Sekido
for his great eﬀorts in organizing this workshop
and publication and is grateful to Dr. Bo Zhang,
Ms. Yongchen Jiang and Mr. Shibiao Dou for
their great support on my studies on the SHAO [10] Evelyn De Wachter, Alexander Haefele,
WVR. The author also expresses great thanks to
Niklaus Kämpfer, Soohyun Ka, Jung Eun Lee,
Dr. Zhiqiang Shen and Dr. Qinghui Liu who giveand Jung Jin Oh, IEEE TRANSACTIONS
me a chance to study on a water vapor radiometer
ON GEOSCIENCE AND REMOTE SENSin Shanghai Astronomical Observatory.
ING, VOL. 49, NO. 3, pp. 1052-1062, MARCH
2011
References[11] Jung-ho Cho, Axel Nothnagel, Alan Roy, and[1] Peter Forkman, Patrick Eriksson, Anders
Ruediger Haas, A generalized scheme to reWinnberg, The 22 GHz radio-aeronomy retrieve wet path delays from water vapor raceiver at Onsala Space Observatory, Journal ofdiometer measurements applied to European
Quantitative Spectroscopy & Radiative Transgeodetic VLBI network, 4th IVS Generalfer, 77, pp. 23-42, 2003
Meeting, Concepcion, Chile, Jan. 9-11, 2006
[2] Alan B. Tanner and A. Lance Riley, Design[12] Gunnar Elgered and Per O. J. Jarlemark,and performance of a high-stability water vaGround-based microwave radiometry andpor radiometer, RADIO SCIENCE, VOL. 38,
long-term observations of atmospheric water
NO. 3, 8050, doi:10.1029/2002RS002673, 2003
vapor, Radio Science, Volume 33, Number 3,
Pages 707-717, May-June 1998
[3] Balthasar T. Indermuehle,Michael G. Burton
and Jonathan Crofts, Water Vapour Radiome-

November 2016

9

Status on the Ishioka Geodetic In August and September 2016, we set up thebroadband observing system and carried out theObserving Station
broadband observations at Ishioka. Two kinds ofbroadband feeds were available at Ishioka: One is
the Eleven feed developed by the Chalmers UniverMasayoshi Ishimoto
sity of Technology in Sweden, and the other is the(ishimoto-m96pu@mlit.go.jp),
Quadruple-Ridged Flared Horn (QRFH) developed
Michiko Umei, Takahiro Wakasugi, Ryoji
by California Institute of Technology. We evaluKawabata, Tomoo Toyoda, Basara
ated receiving performance of these feeds. We also
Miyahara, Yoshihiro Fukuzaki
developed the frequency Up-Down Converter and
the K6/iDAS Sampler for the broadband system
Geospatial Information Authority of Japan,
and evaluated their operational performance. Then
Kitasato-1, Tsukuba, Ibaraki, Japan
Ishioka carried out the broadband observations usAbstract: The Geospatial Information Authority of ing these equipment.
Japan (GSI) has constructed a new VGOS station,
This paper gives the results of the legacy S/Xwhich is named Ishioka Geodetic Observing Sta- band observations and the present status of thetion. The construction of the antenna (radio tele- equipment and the broadband observations.
scope) was completed in March 2014, and an operation building was constructed in February 2016. 2. Observing facility
At present we carry out legacy S/X-band interThe Ishioka Geodetic Observing Station is lonational observations and temporarily install thecated at about 17 km northeast of the Tsukuba staequipment for broadband observations, including
tion. Figure 1 shows the location and an overview
front-end and back-end.
of the Ishioka station. Since the Ishioka station
We report the geodetic results of the legacy S/Xis designed to contribute to Global Geodetic Obband observations and trial broadband observaserving System (GGOS) as a core observatory, ittions carried out at Ishioka in collocation with ﬁve
has a GNSS CORS (Continuously Operating RefIVS stations.
erence Station) and a gravity measurement facility
in addition to the VGOS antenna.
1. Introduction
The Geospatial Information Authority of Japan(GSI) has constructed a new geodetic observing
facility since 2011. This facility is designed forthe next-generation VLBI system called VGOS,
which is promoted by the International VLBI Service for Geodesy and Astrometry (IVS). The construction of the VGOS antenna was completed, andthe other necessary equipment (front-end, backend, hydrogen masers, and so on) was also deliveredin March 2014. The detailed speciﬁcations of theantenna and the delivered equipment are reported
in Fukuzaki et al. (2015). Construction of an operation building was then completed in February
2016. This new geodetic observing facility, called
Ishioka Geodetic Observing Station, will be a main
geodetic VLBI station in Japan as the successor of
the Tsukuba 32-m station from 2017.
At present we carry out the legacy S/X-band
international observations at both Ishioka andTsukuba in order to obtain a precise tie vector
between these two antennas. Ishioka started thelegacy S/X-band observation in 2015, and continued the observation until July 2016. Ishioka will
resume the legacy S/X-band observation in October 2016 after an interruption of two months during Figure 1. Location and overview of Ishioka Geodewhich we carry out trial broadband observations at tic Observing Station
Ishioka.

IVS NICT-TDC News No.36

10

3.

Result of the legacy S/X-band observa- that SEFD (System Equivalent Flux Density) valtion
ues of Eleven feed were higher than that we expected for over 10 GHz frequency (e.g., 7500 Jy for
The Ishioka station carried out the ﬁrst legacy
14 GHz) (Fukuzaki et al, 2015). Then, we meaS/X-band observation in January 2015, and fortysured SEFD values of QRFH to evaluate the resix 24-hour observations were carried out in toceiving performance. The SEFD values of QRFH
tal until July 2016. Table 1 shows the number
are shown in Figure 3. These values were measuredof observations carried out at Ishioka. Figure 2
using the radio signals from a strong radio source,shows time series variation of the estimated baseTaurus-A. This ﬁgure shows that the SEFD valline length between Ishioka and the Tsukuba 32-m
ues of QRFH are reasonably good from 3 GHz toantenna. There are two interruptions during the
14 GHz. The signals less than 3 GHz were cut byobservations because of re-adjustment of the equipa high pass ﬁlter, because the radio signals fromment and construction of the operation building.
Radio Frequency Interference sources were strong
The average of standard deviations of the ﬁve obenough to cause saturation of the receivers. In conservations before September 2015 is about 3 mm
clusion, we determined to employ the QRFH sysand quite large, because artiﬁcial radio signals in
tem as the broadband feed.
the frequency range less than 2.1 GHz were strong
enough to degrade observation signal quality in therange. Therefore we installed a high pass ﬁlter to
cut less than 2.2 GHz, a notch ﬁlter to cut 2.1 GHz,and a band pass ﬁlter to pass 2.2-2.4 GHz after the
Low Noise Ampliﬁer output. As a result, the average of standard deviations after September 2015 issigniﬁcantly improved and about 1 mm.
Table 1. Number of observations
Session TypeJADEAOVIVS-R1
IVS-T2 etc
Total

Number of observations
17
9
17
3
46

Figure 3. SEFD values of Ishioka VGOS antenna
with QRFH

4.2

Frequency Up-Down Converter

We developed a new frequency converter, the frequency Up-Down Converter, compliant with the
VGOS concept. This converter selects any 1 GHz
bandwidth signal between 2 GHz and 14 GHz andconverts the frequency to 1-2 GHz band. Thisequipment composes one control unit and four conversion units (Figure 4). One conversion unit has
two outputs for both horizontal and vertical polarization components. Therefore four bands (eightchannels) signals can be handled in total. In thisequipment, input signal is ﬁrst up-converted to 28
GHz band and then down-converted to 1-2 GHz
band. The block diagram of this equipment isFigure 2. Variation of baseline length between Ish- shown in Figure 5. Because the local oscillator freioka and Tsukuba 32m antenna
quency for up-conversion is programmable between
15.440 GHz and 26.416 GHz, any 1 GHz bandwidth
signal between 2 GHz and 14 GHz can be converted
4. Status of equipment for broadband ob- to 1-2 GHz band.
servation
4.3 Sampler
4.1 Front-end
We developed a new sampler called K6/iDAS.
Eleven feed and QRFH were evaluated as candiThe
speciﬁcations of K6/iDAS are listed in Table
dates for a broadband feed at Ishioka. We found2. The K6/iDAS supports two sampling modes:

November 2016

11

Figure 5. Block Diagram of frequency Up-Down Converter for one conversion unit

Table 2. Speciﬁcations of K6/iDAS sampler installed at Ishioka station
Parameterwide-band mode
maximun data rate
sampling rate

Figure 4. Photo of frequency Up-Down Converter
installed at Ishioka station

bits
channels
DBBC mode
maximun data rate
sampling ratebits
channelsValue4096 Mbps
256, 512, 1024, 2048
Msps
1-8 bit14096 Mbps
8, 16, 32, 64, 128 Msps
1-8 bit
1, 2, 4, 8

on 9 August 2016. The details of this observation
are shown in Table 3. The ﬁrst fringes of the international broadband observation for Ishioka weredetected between Ishioka and Hobart. In the caseof this observation, our frequency Up-Down Converter and K6/iDAS Sampler were not used, instead, another AD sampler K6/GALAS, which wasdeveloped by NICT (Sekido et al., 2015), was used.
After the observation Ishioka participated in theother two broadband observations (VGT003 and
VGT004) planned by IVS on 11 and 30 August (Ta4.4 Broadband observationble 3). The fringes were not detected for VGT003
Ishioka carried out the ﬁrst international broad- probably due to incorrect frequency settings. On
band observation with the Hobart 12-m antenna in the other hand, for VGT004, the fringes were deAustralia and the Kashima 34-m antenna in Japan tected successfully. This is the ﬁrst fringe for our
One is wide band mode, which samples 1 GHz
bandwidth directly with 4 Gbps (2 bit and 2 GHz)
recording rate, the other is Digital Base Band Converter (DBBC) sampling mode. Since this sampler
is under evaluation, we also use ADS3000+ AD
Samplers developed by National Institute of Information and Communications Technology (NICT)and Institute of Space and Astronautical Science(ISAS) for broadband observations.

IVS NICT-TDC News No.36

12

Table 3. details of Broadband observations
Parameter
Value
HK16222 with Hobart and Kashima
Date
9 and 10 August 2016
Frequency (center)
4360,
5112,
9960,
12860 MHz
Bandwidth of one 1024 MHz
band
Sampling rate
2048 Msps
bits
2
Polarization
Verticalchannels
1 ch x 4 bands
VGT003 and VGT004
Date
10 and 30 August 2016
Frequency (center)
3240.4, 5480.4, 6600.4,
10440.4 MHz
Bandwidth of one 512 MHz
band
sampling rate
1024 Msps
bits
2
Polarization
Horizontal and Verticalchannels
16 ch x 4 bands

new system with frequency Up-Down Converterand ADS3000+ AD Sampler. For the next step Ishioka will carry out an international 24-hour broadband observation in September 2016.

5.

Summary

Construction of the Ishioka Geodetic Observing
Station was completed in February 2016. Ishioka
has mainly carried out the legacy S/X-band observations, and the reasonable geodetic results wereobtained. In addition, we almost ﬁnished installation of the equipment for the broadband observation at Ishioka. Ishioka carried out two international broadband observations in August 2016, andthe fringes were successfully detected. Ishioka will
carry out an international 24-hour broadband observation in September 2016 and resume the legacy
S/X-band observations from October. In 2017, we
will carry out both the broadband and the legacy
observations.
6.

Acknowledgments

We would like to thank colleagues of NICTSpace-Time Measurement Group for their generous assistance on the broadband observations. We
also acknowledge colleagues of NASA/GSFC andUniversity of Tasmania for their cooperation in the
broadband observations.
References[1] Fukuzaki, Y., K. Wada, R. Kawabata, M. Ishimoto, and T. Wakasugi, First Geodetic Resultof Ishioka VGOS Antenna, IVS NICT-TDC
News No.35,pp.1-3,2015.
[2] Sekido, M., K. Takefuji, M Tsutsumi, andT. Kondo, Broadband VLBI Data Acquisition
System for GALA-V, IVS NICT-TDC News
No.35,pp.7-11,2015.

November 2016

Developmentof Wideband Antenna

Hideki Ujihara (ujihara@nict.go.jp)
Kashima Space Technology Center,
National Institute of Information
and Communications Technology,893-1 Hirai, Kashima, Ibaraki 314-8501, Japan
1.

13

2.

Plans

New wideband OMT and NINJA feeds will be
developed in this year to replaced the current NIJNA feeds. They can cut RFI in the 2 GHz band
and will improve the aperture eﬃciencies of our 34
m and 2.4 m antennas. Observations with dual
polarization will be started soon after the replacement of the NINJA feed in the 34 m. Wideband
OMTs will be developed for the IGUANA feeds.

Status of development

New wideband feed, NINJA Feed, has installedin the Kashima 34m antenna in the last summer.
The NINJA feed was designed for 3.2-14.4 GHz andwas mounted nearby the IGUANA Daughter feed
which is operated in 6.5-15 GHz band as shownin Figure 2. The main reﬂector of the MARBLE
at NICT Koganei was enlarged from 1.6 m to 2.4
m and its optics was changed to the Cassegrainwith another type of the NINJA, as shown in Figure 3. They are operated with 30-40 % apertureeﬃciency, but receiving frequencies of both antennas are limited by the WRD350 to SMA converters
now. Also new wideband OMT for these NINJA
feeds was developed as shown in Figure 1. ThisOMT was tested with the NINJA feed in the 34
m antenna, but strong RFI from cellular phones
in 2 GHz band was received. Thus observations
with dual polarization will not be started after new
OMT is designed and fabricated.

Figure 2.
The NINJA feed and the IGUANA feed in the
Kashima 34m receiver cabin.

Figure 1.
Return loss measurement of the new wideband
OMT with the NINJA feed for the MARBLE.

Figure 3.
MARBLE 2.4m on the roof top of the NICTKOGNEI 2nd building.

14

IVS NICT-TDC News No.36

Development Status of GALAV Broadband VLBI — Geodetic Solution and Clock Comparison –M. Sekido1 (sekido@nict.go.jp),
K. Takefuji1 , H. Ujihara1 , T. Kondo1 ,Y. Miyauchi1 , M. Tsutsumi1 , E. Kawai1 ,S. Hasegawa1 , J. Komuro2 , R. Ichikawa2 ,Y. Koyama2 , Y. Hanado2 , K. Terada2 ,K. Namba2 , R. Takahashi2 , T. Aoki2 ,T. Ikeda2 , R. Kawabata3 , M. Ishimoto3 ,T. Wakasugi3 , Y. Umei3 , T. Toyoda3 ,K. Watabe4 , T. Suzuyama4 1)
NICT/Kashima Space Technology Center,893-1 Hirai, Kashima Ibaraki, Japan.
2) NICT/Headquarter, 4-2-1 Nukui-Kita,
Koganei, Tokyo 184-8795, Japan.
3) Geospatial Information Authority of Japan., 1,
Kitasato, Tsukuba 305-0811, Japan.
4)National Meteorology Institute of Japan,
Umezono, Tsukuba 305-8563, Japan
Abstract: Development of broadband VLBI system named GALA-V has been conducted by NICT
for VLBI application to distant frequency transfer. Observation systems and signal chain fromdata acquisition to analysis has become ready. A
series of broadband VLBI sessions with pair ofsmall diameter antennas and high sensitivity antenna (Kashima 34m or Ishioka 13m) have been
performed since Jan. 2016. VLBI delay data on
the baseline between small antenna pair were notdirectly derived by the cross correlation of thesedata set, but that was computed by linear combination of delay observables between small antennas and high sensitivity antenna baselines. Geodetic solutions of seventy km baseline between 1.6m
and 2.4m diameter antennas were obtained by thevirtual observables. The repeatability of the station coordinates were several millimeters in horizontal and a few centimeter in vertical position.
Atomic clock behaviors between two small stations
are obtained from these VLBI sessions and they are
consistent with those derived by GPS observations.
This paper reports overview of the system development and data analysis results of broadband VLBI
sessions in 2016.

Figure 1. Pictures of VLBI antennas, which are capable of broadband observation in Japan. (a) MARBLE1 1.6m, (b)MARBLE2 2.4m, (c) Kashima
34m, (d) Ishioka 13m.

range 3-14 GHz has been motivated for improvement in sensitivity and delay measurement precision, and joint observations with VGOS stations
are in the scope. The GALA-V system has target of making distant frequency comparison between transportable small VLBI stations by thehelp of joint observation with high sensitivity VLBI
stations. Advantages of using small antennas aremainly two folds. Firstly, features of lower cost andtransportability are suitable as a tool for frequency
comparison of atomic time standards. Secondary,large diameter antenna has potential cause of delay
ﬂuctuation such as distortion of antenna structure
and long signal transmission lines. Those eﬀects
related with large diameter antenna are canceledout in the linear combination of the equation (1).
Magnitude of distortion is proportional to the sizeof the antenna, thus potential error sources are reduced for small antenna.
Signal to noise ratio (SNR) of VLBI observation
is proportional to the products of two observing
stations of the baseline. Thus disadvantage of lower
sensitivity of small antenna pair (A and B) is compensated by joint observation with high sensitivity
station (R). Even SNR was not enough on A-B
baseline, as far as R-A and R-B baselines works as
1. Introduction
interferometer, delay observable of small antenna
NICT is conducting development of broadband pair τAB can be computed by linear combination
VLBI system named GALA-V for distant frequency transfer [1]. Broad observation frequency

November 201615

of delay observable τRA , τRB as follows:τAB (tprt ) =τRB (tprt − τRA (tprt )) − τRA (tprt − τRA (tprt ))∼= τRB (tprt ) − τRA (tprt )−dτAB (tprt ) × τRA (tprt ) (1)dt
It should be noted that this is valid when the radiosource is supposed as a point source with respect
to the fringe spacing in the sky formed by the projected baseline. Radio source structure eﬀect haveto be considered when the brightness distributionof the radio source is not negligible. This assumption is valid for the experiments described in thispaper due to short baselines.
Based on this idea, broadband VLBI stations ofsmall antenna pair and high speed data acquisition
systems have been developed. Fig. 1 shows VLBI
stations, which is capable of broadband observation in Japan. Kashima 34m station and small diameter broadband stations MARBLE1 and MARBLE2 have become ready for operational broadband observations in 2016. Ishioka 13m station of
Geospatial Information Authority of Japan (GSI)
has started its operation since 2015. This report
describes current status of broadband system development, and some results of broadband VLBI
sessions conducted in 2016.
2.

Development of Broadband VLBI System GALA-V

2.1

Broadband VLBI Antennas

Kashima 34 m diameter VLBI station has been
upgraded by installation of our original broadband
feed systems. The ﬁrst prototype feed IGUANAH, which has sensitivity at 6.5-15 GHz[2, 3], wasinstalled in 2014. The next feed NINJA was designed for 3.2-14.4 GHz frequency range[4], andit was mounted on the 34 m antenna in 2015.
System temperature and System Equivalent Flux
Density (SEFD) are about 200-300 Kelvin and1500-2000 Jansky for 3-11 GHz frequency range,
respectively[5].
A pair of small diameter antennas MARBLE1
and MARBLE2 have been originally developed
for the project of baseline evaluation[6]. Bothof these antennas are equipped with Rindgren
Quadridge Flared Horn (QRFH)s and room temperature LNAs, and frequency downconverter for
S/X-band had been used in that project. We
have upgraded them to enable broadband observation for GALA-V project. One of two broadband transportable antennas (MARBLE1 of 1.6m
diameter) has been installed at National Instituteof Metrology in Japan (NMIJ) at Tsukuba. The
other antenna (MARBLE2 of 1.5m diameter) has
been placed at NICT headquarter at Koganei.
MARBLE2 1.5 m diameter prime focus antenna using QRFH was upgraded to 2.4 m dish of
Cassegrain optics with second NINJA feed in 2016.
By using room temperature LNA, the system noise
temperature is around 150-200 Kelvins in 3-11 GHz
frequency range. After that evaluation of second
NINJA feed at MARBLE2, the third NINJA feed
will be installed to MARBLE1 antenna, and diameter of the antenna will be upgraded to 2.4 m with
Cassegrain optics in near future. Current system
noise temperature of MARBLE1 antenna is 200300 Kelvins.
Both of two small antennas are capable of only
single linear (Vertical) polarization observation.
Current SEFDs of MARBLE1 and MARBLE2 are
1 ∼ 2 × 106 Jansky, and 2 ∼ 4 × 105 Jansky, respectively in 3-11 GHz frequency range.
2.2

Data Acquisition and Signal Processing

Another new technology introduced in thisproject is ”RF-Direct-Sampling” technique[7],which converts radio frequency analog signal
to digital data by using high speed sampler
K6/GALAS[8] at 16,384 MHz sampling rate without analog frequency conversion. Four bands ofsignals with 1 GHz bandwidth can be ﬂexibly speciﬁed in 0 - 16 GHz frequency range, and they are
extracted by digital signal processing. Then thedata is acquired to high speed recording systemthrough 10G-Ethernet interface. This RF-DirectSampling technique has an essential advantage at
stable phase relation between the signals of eachbands. Since precise group delay observable isobtained by linear phase gradient over broad frequency range, phase distortion caused by the signal transmission line from the radio telescope tothe recording system has to be calibrated. Linear phase characteristics is the key feature to measure precision group delay with broadband signal.
In case of analog frequency conversion, it is inevitable that unpredictable phase oﬀset originatedfrom local oscillator is added in that process. Conventionally, phase calibration signal (Pcal)[9] hasbeen used to calibrate phase characteristics of thesystem including the oﬀset and signal transmission
path, however special care is needed to keep phasestability of the Pcal device itself. Because the timing of Pcal signal is triggered by reference signal,thus its phase can be changed by thermal extensionof reference signal transmission cable. For monitoring and calibration of this change, Delay calibration system (Dcal) has been used at geodetic VLBIIVS NICT-TDC News No.36

16

Group delay(EBW:6.7GHz)Group delay(EBW:6.7GHz)

1e-12

Alan Std Dev.

Delay [psec]

15
10
5
0
-5
-10
-15

1.e-13 x τ

-1/6

1e-13

1e-14
0

200

400

600

800

1000 1200

1Time [sec]

10

100

Interval [sec]Figure 2. Left panel shows time series of broadband VLBI delay data for 3C273B on Kashima 34m Ishioka 13m baseline. Trend of slow delay change including geometry and clock has been subtracted bypolynomial ﬁtting. Every points of 1 sec. interval represents delay data obtained by synthesizing four
frequency bands. The random walk like delay behavior, which changes about 20 ps in a few hundred
seconds, might be caused by atmospheric delay ﬂuctuation. Right panel shows Alan standard deviation
computed from the delay data in the left panel. Dashed line indicates σ(τ ) = 1 × 10−13 τ −1/6 , which is an
example of ﬂuctuation evaluated by Kolmogorov turbulence theory and coeﬃcient in literatures[12, 13].
stations. Whereas in case of RF-Direct-Sampling,phase relation among the four bands of signal isfrozen at the point of digitization.
For recovery of linear phase characteristics over
the wide frequency range, we employed a phase calibration method using reference radio source. Radio sources with relatively stronger ﬂux are observed a few times in a session, then one of thescans with high SNR is chosen as template for calibration. The cross correlation phase spectrum of
the template scan data is applied to all the scans ofwhole session to calibrate the phase characteristics
of signal transmission path and data acquisition.
This method has been proven to work well in our
broadband VLBI sessions.
Polarization of the data acquisition in our VLBI
sessions has been only single linear (Vertical) polarization. Because diﬀerences of paratactic angles are
negligible on these domestic short baselines, this it
not a issue at present. Dual polarization observation is necessary in intercontinental long baseline
observation. And the VGOS speciﬁcation requires
dual linear polarization observation, Dual polarization data acquisition is being prepared in out
GALA-V project, too.
Cross correlation of the data has been processedby using high speed software correlator GICO3[10], which was developed by NICT for astronomical broad band observation. Correlation output of four band of signals are synthesized by
new wideband bandwidth synthesis (BWS) software ’komb’[11]. The BWS produces sharp peakin time domain after phase characteristic calibration by using template scan as described above.
Fig. 2 shows a delay data of radio source 3C273B

obtained by a test experiment on Kashima 34m- Ishioka 13m baseline in 2015. The data showsthat sub-pico second delay precision was achievedby 1 second of observation. It is demonstrating
potential of extremely high delay precision by thebroadband observation system. The random walklike that delay behavior, which changes about 20 ps
in a few hundred seconds, is thought to be caused
by property atmospheric delay change. Alan standard deviation of the data shows consistent trendwith an example of ﬂuctuation (dashed line in theright panel of Fig.2) evaluated by Kolmogorov turbulence theory and coeﬃcient in literatures [12, 13].
3.

Broadband VLBI Sessions in 2016

Basic observation mode of the GALA-V system
was allocating four 1024 MHz width data acquisition bands in 3-14 GHz frequency range with nonredundancy interval. Frequency allocation of band
center at 4.0 GHz, 5.6 GHz, 10.4 GHz, and 13.6
GHz was the original plan. Although by taking
into account practical condition such as radio frequency interference (RFI) and sensitivity of current receivers, slightly narrow frequency allocation
at 5.9, 7.1, 8.7, and 10.6 GHz was used in the VLBI
sessions in 2016.
Eight broadband VLBI sessions have been conducted during period between January to September 2016 (Table 1). Because the target of the
project is frequency comparison of atomic standards, then session lengths are longer than 24 hours
to get clock behavior in long time span. Extracted observation data of broadband VLBI sessions are stored to MK3 database and analyzed by
Calc Ver.11.01 and SOLVE Release 2014.2.21 de-November 201617

Table 1. Broadband VLBI sessions during Jan.-Sep. in 2016. Kas34:Kashima 34m antenna, MBL1:
MARBLE1 antenna, MBL2: MARBLE2 antenna, Ish13: Ishioka 13m antenna.
Date in 2016
Stations
Num. Scans
SessionAvg. time
Used/Recorded Duration/scan
26-27 Jan.
Kas34—MBL1—MBL2
1330/1500
46 h
110 sec.
12-13 Feb.
Kas34—MBL1—MBL2
1250/1600
47 h
106 sec.
28-29 Feb.
Kas34—MBL1—MBL2
1050/1450
49 h
122 sec.
16-17 May.
Kas34—MBL1—MBL2
1220/1410
31 h
79 sec.
24-25 Jun.
Kas34—MBL1—MBL2
1800/1850
49 h
95 sec.
10-11 Jul.
Kas34—MBL1—MBL2
1960/2003
48 h
86 sec.
23-24 Aug.
Ish13—MBL2
1372/1385
43 h
112 sec.
12-13 Sep.
Ish13—MBL1—MBL2
1600/1640
35 h
77 sec.

OA
OB
AB
Gauss Fit to OA
Gauss Fit to OB
Gauss Fit to AB

Occurrence [%]

20

10

0
−150

−100

−50

0

50

100

150

Delay Residual [ps]Figure 3. Post-ﬁt delay residual of AB baseline in the session of 10-11 July, where delay of AB baseline
was computed by linear combination of OA, and OB baselines. (O:Kashima34, A: MARBLE1, and
B:MABLR2). Delay errors evaluated from SNR of BWS results was 4 ps or below for all the scans of
AB baseline. Extra noise of 23 ps was added in the reweighting procedure to make reduced χ2 unity.
veloped by NASA/GSFC(http://gemini.gsfc.
nasa.gov/solve/). Estimation parameters in
VLBI analysis are station coordinates (XYZ), atmospheric delay with Niell’s Mapping Function
with 20 min. interval, and clock parameters in 60
min. interval. Since there is no ambiguity in ourdelay observable due to broad bandwidth, analysis procedure is simply ﬂagging bad data and reweighting of data to make reduced-χ2 unity. Delay
residual of small antenna pair AB baselines in thesession of 10-11 July is displayed in Fig.3.
As described at introduction, correlation processing for AB baseline is not performed, but thedelay data of AB baseline is computed by linear
combination of delays of OA, OB baselines withequation (1). Delay error magnitude of AB baseline
is supposed to increase as root sum square of theerror of OA and OB baseline via error propagation
law. However, post ﬁt delay residual of AB baseline
does not increase as expected. This indicates thepost ﬁt residual is dominated by extra error added
to make reduced-χ2 unity, which is added in thebaseline analysis and that represents un-modeled
delay error. This suggests that degradation of delay error by linear combination process was negligible in these broadband sessions. A series of
MARBLE2 station coordinates estimated with ABbaseline data of broadband sessions are displayedin Fig. 4. By taking into account a linear trend of-10.5 mm/yr in E-W direction, repeatability of horizontal coordinates was about several milli-meters,
and that of vertical coordinates was a few centimeters. Estimated ’Clock+residual’ as the product of
VLBI is plotted in Fig. 5. Their clock behavior isconsistent with GPS ppp-solutions, though variation around the trend is larger on VLBI. Further
improvement need to be investigated.
4.

Summary

Broadband VLBI system GALA-V acquiring
four 1 GHz band width in 3-14 GHz frequency
range has now been ready for single linear polarization observation. Original designed broadband

IVS NICT-TDC News No.36

18

N−S [mm]E−W [mm]

U−D [mm]

01

02

03

04

05

06

07

08

09

40

40

30

30

20

20

10

10

0

0

−10

−10

−20

−20

−30

−30

−40

−40

10

10

0

0

−10

−10

10

10

0

0

−10

−10
01

02

03

04

05

06

07

08

09

Month in 2016

Figure 4. Series of MARBLE2 station coordinates estimated with AB baseline data are displayedfor UP-Down, East-West, and North-South coordinates. Error bars of each point indicates formal
error of the coordinates in each session. A linear
trend of -10.5 mm/yr was observed in East-Westdirection, which we suppose to be due to local eﬀect.
By taking into account removing this trend only in
East-West coordinates, repeatability of the MARBLE2 station coordinates w.r.t the MARBLE1 coordinates are several milli-meters in horizontal andabout a few centi-meters in vertical coordinates.
feeds have been developed to satisfy the conditionsof broadband receiving and narrow beam width
for Cassegrain focus. A new technique RF-DirectSampling by using K6/GALAS sampler demonstrated simpliﬁed data acquisition system without
Pcal device. This system is working eﬀectively forstable broadband delay measurement. Broadband
bandwidth synthesis software was developed and it
resulted ever achieved sub-pico second group delay
measurement by broadband VLBI experiment. A
series of broadband domestic VLBI sessions with
GALA-V system have been conducted. VLBI delay data on the baseline of small diameter antenna
pair were computed by linear combination of delay data with respect to larger antenna, and it was
analyzed by CALC/SOLVE system. Repeatability
accuracy of the geodetic solution of small antenna
pair was several millimeters and a few centimeters in horizontal and in vertical coordinates, respectively. Atomic clock diﬀerence estimated a by
VLBI observation between small diameter antenna

Figure 5. An example of ’Clock+residual’ obtained
by VLBI data in Feb. 12-14 session is plotted.
Marks of (’+’, ’x’, ’*’,’2’) are solution of single
1 GHz band at 5.9 GHz, 7.1 GHz, 8.7 GHz, and10.6 GHz. The solid line and closed circle is broadband delay by synthesis of all bands. GPS analysis
results is plotted with open circles. Vertical position of the VLBI data is shifted appropriately forcomparison.
pair has been successfully estimated. It shows consistent results with that measured by GPS observation.
Dual linear polarization observation will be indispensable in intercontinental broadband VLBI
observation. Source structure eﬀect may have to
be considered in long baselines. We need development of data processing scheme of mixed polarization data, and further improvement of precision is
subject for the next step.
5.

Acknowledgments

Development of broadband receiver system was
supported by grant (2013 -2014) of Joint Development Research from National Astronomical Observatory of Japan(NAOJ). We appreciate the support from research network provider JGN for highspeed network environment.
References[1] M. Sekido, K. Takefuji, H. Ujihara, M. Tsutsumi, S. Hasegawa, Y. Miyauchi, E. Kawai, R.
Ichikawa, Y. Koyama, and T. Kondo, ”Status of Broadband VLBI Observation System(GALA-V) Development”, IVS NICT-TDC
News. No. 34, pp.17-19, 2014.
[2] H. Ujihara, K. Takefuji, M. Sekido, “Development of Wideband Feed” IVS NICT-TDC
News. No. 34, pp.28-31, 2014.

November 2016
[3] Ujihara, H., ”Development of Wideband Feed
for Kashima 34 m Antenna” submitted to Radio Science, 2016.
[4] H. Ujihara, K. Takefuji, M. Sekido, “Development of Wideband Feed” IVS NICT-TDC
News. No. 35, pp.12-13, 2015.

19[8] Mamoru Sekido, Kazuhiro Takefuji, Masanori
Tsutsumi, and Tetsuro Kondo, ”Broadband
VLBI Data Acquisition System for GALA-V”,
IVS NICT-TDC News No.35., pp.7-11, 2015.
[9] T.Clark, et al., “Precision Geodesy Using
the Mark-III Very-Long-Baseline Interferometer System”, IEEE Trans. on Geosci. and Remote Sens., Vol., GE-23, No.4, 1985.

[5] M. Sekido, et al., “An Overview of theJapanese GALA-V Wideband VLBI System”,
The 9th IVS General meeting Proceedings, in [10] M.Kimura, ”Development of the software corprinting, 2016.
relator for the VERA system III”, IVS NICTTDC News. No. 29 pp.12-14, 2008.
[6] R. Ichikawa, et al.., ”MARBLE (Multiple
Antenna Radio-interferometry for Baseline [11] Kondo, T., and K. Takefuji, “An alLength Evaluation): Development of a Comgorithm of wideband bandwidth synthepact VLBI System for Calibrating GNSS
sis for geodetic VLBI”, Radio Sci., 51,
and Electronic Distance Measurement Dedoi:10.1002/2016RS006070, 2016.
vices”, IVS 2012 General Meeting Proceedings”Launching the Next-Generation IVS Net- [12] Thompson.R, J. Moran, and G. Swenson, ”Interferometry and Synthesis in Radio Astronwork” Edited by Dirk Behrend and Karen D.
omy”, Krieger Pub. Com. 1994.
Baver, NASA/CP-2012-217504, pp.161-165,
2012.
[13] Armstrong, J.W., and R.A.Shramek, ”Obser[7] K. Takefuji, et al., ”High-order Sampling
Techniques of Aliased Signals for Very Long
Baseline Interferometry”, Publ. Astron.Soc.
Paciﬁc, Vol.124, pp.1105-1112, 2012.

vations of Tropospheric Phase Scintillations at
5GHz on Vartical Paths”, Radio Sci., Vol 17,
pp.1579-1586, 1982.

20

Performance of Direct Sampler
K6/GALASIVS NICT-TDC News No.36

GHz and tuned down-conversion frequency of thesampler to become the 1 MHz higher than lower
edge of the input signal. The synthesizer and theK6/GALAS were synchronized by an external reference signal. Since the sampled frequency was
Kazuhiro Takefuji (takefuji@nict.go.jp)2048 MHz, the input signal would rotate 1 million
1times in 1 s. Then, we performed the Fourier transKashima Space Technology Center, National
formed with 2048 points and obtained the millions
Institute of Information and Communicationsof phase data.
Technology, 893-1 Hirai, Kashima, Ibaraki
The phases are shown in Figures 4 and 5. The
314-8501, Japanvariation of the phase becomes bigger as input
Abstract:
signal became higher frequency. Then, we calcuWe have been developing a broadband VLBI lated the standard deviation of each frequency resystem so-called Gala-V, which meets the VGOS sults. It is shown in Figure 2, where we obtain(VLBI2010 Global Observing System) require- the ﬁtted slope (0.0689 deg/GHz = 0.191 ps) as
ments. The direct sampler, so-called K6/GALAS a jitter. Based on the obtained jitter value. The
is a key component of the our project. Here we re- K6/GALAS is expected a good sampler even theport an evaluation of K6/GALAS including jitter input frequency of 20 GHz.
and frequency response.
2.2 Frequency response measurement
1. The Direct Sampler, K6/GALAS
K6/GALAS has a capability of receiving signal
Figure 1 shows the design of K6/GALAS. It to K-band. Thus, we measured the frequency rehas four analog inputs and four 10 GbE outputs. sponse of K6/GALAS precisely. We conducted theK6/GALAS samples an input signal at 16 GHz measurement in the following way, we input the
speed and 3 bits quantization. K6/GALAS realized sine wave from the synthesizer to the K6/GALAS
the down-conversion with high order sampling or and capture the bit distribution, 3-bits (8-steps).
digital baseband conversion of digital signal tech- At ﬁrst we input the 1 GHz signal with -8.5 dBmnique inside.
and recorded the bit distribution as a reference.
Actually, the RF signal of the range of 3 to 15 Then, we input several frequencies up to 20 GHz.
GHz from Kashima 34 meter radio telescope is As a matter of course, the bit distribution becomestransferred without frequency-conversion through narrow as an input signal becomes higher. We adhigh sensitivity optical ﬁber from antenna cabin to justed the power level of the synthesizer to be theour observation room. Then, the signal after some same bit distribution as the reference. Note that
ampliﬁed inputs to the K6/GALAS. Currently we we measured and corrected the cable loss for the
installed the low-pass ﬁlter and high-pass ﬁlter of input power. Table 2 shows the result of the bit
the frequency of 8 GHz before input the signal distribution in each input frequencies. The result
to the K6/GALAS because the frequency of 8.192 of the 22 GHz was within 1-bit level, we input the
GHz is the half sampling speed (see Table 1).
power level of -3 dBm of 22 GHz separately and readjusted the reference distribution. Figure 3 shows
2. Evaluation of K6/GALAS
the result of the frequency response of K6/GALAS
from comparing amplitude from quantized bit dis2.1 Jitter measurement
tribution between reference signal. Currently, we
The internal digital baseband conversion or high- input the signal from the antenna of 3 to 15 GHz
order sampling method converts the high frequency range to the K6/GALAS, and the signal splits
signal to a baseband frequency. Thus, the direct lower and higher side of 8 GHz. Thus, a few dB
sampler should have a high stability frequency re- diﬀerence should be considered for better observasponse. This is expressed by ”jitter” in time do- tions.
main or ”phase noise” in frequency domain.
K6/GALASis
produced
andmainAt ﬁrst, we evaluated the jitter performance. We tained by ELECS Industry co.,ltd.
http:input a sinusoidal signal from a signal synthesizer //www.elecs.co.jp/ElecsIndustry/download/
to K6/GALAS at each frequencies, then calculated index.html#giga-sampler
the jitter from digitized signal. K6/GALAS samples the signal in 3 bit and 16.384 GHz sampling
speed and the signal becomes down-converted digitally inside the sampler. We input several frequency from the synthesizer from 1 MHz to 14

November 201621

Table 1. Specﬁcations of direct sampler K6/GALASFrequency range
Number of analog input
Sampling rate
Quantization
DBBC
10GbE protocol

0.01 to 24 GHz
2 (optionally 4)16384 or 12800 MHz
3 bit
1GHz bandwidth, 2 bit, 4 streams
VDIF / VTP/ UDP / IP

Table 2. Measured the bit distribution of K6/GALAS as the frequency input from the synthesizer. Since
the result of 22 GHz becomes within the 1-bit level, we measured separately.
CW[GHz]1, reference
4
6
7
8
9
10
12
16
20

0
0
0
0
0
0
0
0
0
0
0

1
25
18
13
7
0
1
1
0
0
0

2
12
17
20
25
29
30
30
20
15
0

bit step [%]345
14 12 1117 15 16
18 16 19
19 17 22
21 19 31
20 17 29
19 17 31
32 28 20
36 36 1349 51 0

6
26
17
14
10
0
3
2
0
0
0

7
0
0
0
0
0
0
0
0
0
0

Figure 1. The design of the direct sampler Galas and its appearance.

IVS NICT-TDC News No.36

22
1.4

Phase noise [deg]

1.2
1
0.8
0.6
0.4
0.2
0

2

4

6

8

10

12

14

16

Frequency [GHz]

Figure 2. The jitter performance of the direct sampler Galas
0

Attenuation [dB]

-1
-2
-3
-4
-5
-6
-7
-8
0

2

4

6

8 10 12 14
Frequency [GHz]

16

18

20

2

2

1.5

1.5

1

Phase [degree]

Phase [degree]

Figure 3. The frequency response of the direct sampler Galas

0.5
0
-0.5
-1
-1.5

1
0.5
0
-0.5
-1
-1.5

-2

-2
0

20000

40000

60000

80000 100000

0

20000

Time [100 ms]

40000

60000

80000 100000

Time [100 ms]

Figure 4. Time-series of the phase, left shows the 1 MHz and right shows the 2GHz input.

4Phase [degree]

Phase [degree]

4
2
0
-2
-4

2
0
-2
-4

0

20000

40000

60000

Time [100 ms]

80000

100000

0

20000

40000

60000

80000

100000Time [100 ms]

Figure 5. Time-series of the phase measurement, left shows the 7 GHz and right shows the 12 GHz
input.

November 2016

23

VERICA, A New Verification contain residual systematic errors. The ﬁrst cases
existences of outliers largely deviated from esMethod of Applied Calibra- aretimated distributions of diﬀerential thermal noise.
tions onto Visibility Data (II) Both the subsets (a) & (e) are cases of quite higher

Makoto Miyoshi (makoto.miyoshi@nao.ac.jp)
National Astronomical Observatory Japan,
2-21-1 Osawa, Mitaka Tokyo, Japan 181-8588
Abstract In the NICT TDC Symposium in 2014,
we introduced a method of veriﬁcation of data calibration by checking diﬀerential visibility between
IF channels (Miyoshi 2014) [1]. Raw visibility
data includes structure information of the observed
source, an independently ﬂuctuating thermal noise,
and a systematic error. Data calibration is performed in order to eliminate the systematic error
in the visibility. After calibrating the individual
recording channels independently, if the systematic error remains partly, the residual systematic
error is independent for each channel. When thesignal-to-thermal noise ratio is small, it is often insuch a state. By creating diﬀerential visibility between independently calibrated recording channels,
the information of the source structure is common,so they are erased, and what lie there are the diﬀerence between the thermal noises and the diﬀerenceof the residual system errors. If the behavior is
diﬀerent from that of the thermal noise expectedfrom the sensitivity of the baseline, there will be
residual systematic errors in the visibility data after the calibration is performed. Here, we show
examples in which residual system errors can befound in calibrated data using this method, VERICA (veri ﬁcation method of ca librations onto
visibility data), and demonstrate the generality of
the VERICA method.

signal to noise ratios than 7 (in 10 seconds integration). Almost of the sampled data are ﬁtted wellto only thermal noise distributions, but there are
outliers as indicated by arrows. In the case of (e),the χ2 value is more than 6 × 1010 due to the outliers.
The second cases show non-zero-mean distributionsof diﬀerential visibility. If the errors are thermal
noises only, the mean of diﬀerential visibility distribution must be zero. While the subsets, (b) and(f) show deviations towards left side from zero as awhole, clearly this is due that one of the IF channels
have not a proper, constant oﬀset in calibration solutions.
Single peak at zero is other feature of the distributions of diﬀerential visibility containing only thermal noises. (The unique exception is the distributions of diﬀerential phases with ”no signal”: In thiscase, the distribution shows not a peak but a constant value.) The last cases show not a single peakat zero but multiple peaks. The subsets of (c), (d),(g), & (h) belong to the last cases. The subset(c) shows that multiple peaks distributed in a wide
range and that the maximum peak position is notat center (at zero). This may be due to the few
number of samples (Ndata = 109), but the maximum peak must be located at zero regardless of thesignal to noise ratio in diﬀerential amplitude distributions. The subset (d) shows comparable twin
peaks: one is at zero and the other is at a minus
value. The peaks at the minus value presumably
due to residual systematic errors. The subsets (g)& (h) also show twin peaks but in these cases, bothare located not at zero, suggesting the existence ofresidual systematic errors.
2.

1.

Cases of residual systematic errors
found by the VERICA methods

In Miyoshi 2014 [1], we showed the examples
that has no residual systematic error in the calibrated data of Miyoshi et al. 2011 [2]. From thesame data set, this time we show the cases residual systematic errors are still contained in the calibrated data in Figure 1. There are 8 of subsets:(a), (b), (c), & (d) are examples from diﬀerential
amplitude between IF channels, while (e), (f), (g),& (h) are those from diﬀerential phase. Distributions shown in Figure 1 have diﬀerent features fromthermal noise ones, suggesting that some residual
systematic errors still exist after the calibration.
There are three types of distributions that seem to

An example of the VERICA application:a case of no signal noise data

Here we show the case of VERICA application tono signal dataset. The calibrated visibility dataset
shown here is from Miyoshi et al. (2003) [3]. They
simultaneously observed two of SiO maser lines,
namely the v= 1 and v=2 (J =1-0) from VY CMa
using the VLBA at Q-band. They performed calibrations of visibility data of the two baseband
channels independently. The ﬁnal image and thecalibrated visibility after Hybrid mapping showedaccordance in closure phase less than 2◦ . In Figure 2, we show those of three baselines, the shortest
baseline LA-PT (237 km), a modest one HN-OV(3886 km), and the longest one MK-SC (8612 km)
in the VLBA. The histograms of diﬀerential phase

IVS NICT-TDC News No.36

24

in the lower panels show ﬂat distributions thatmean the SNRs of the channels equal zero, namely
free from maser emissions. Not only these three
examples but all diﬀerential phases of 45 baselines
show ﬂat distributions. While the histograms ofdiﬀerential amplitude in the upper panels show different features from the nature of pure thermal
noises with the expected levels. First, the estimated thermal noise from theoretical curve ﬁtting
to the histograms are 5±0, 12±0, 23±0 mJy, which
are too low noise levels to be explained from themeasured system temperatures. Second, there areseveral outliers in the bins away from zero. Third,
all of the three histograms of diﬀerential amplitude
show asymmetric features having oﬀsets towards
minus direction in the x-axis, which cannot be explained by thermal noise. This may be from diﬀerent noise levels due to the large frequency diﬀerence between the channels. One was for receiving
the SiO v=1, the J=1-0 transition at 43.1 GHz,
the other was for receiving the SiO v=2, the J=1-0transition at 42.8 GHz. The diﬀerence of frequencies was 305 MHz. The receiver might have not a
ﬂat band path character. Anyway, investigations of
the diﬀerential amplitude distributions allow us tojudge that the amplitude calibrations of the data
were poorly performed and not a few systematic
errors remained after the calibration. As for thephase calibrations of the data, it was performed
with very high accuracy as well as 2◦ in closure
phase. While as for the amplitude calibrations of
the data, there were unknown problems so that nota few residuals of amplitude systematic errors in
the calibrated data. Thus, it is demonstrated that
the VERICA method is useful especially for conﬁrming the amplitude calibrations.
References[1] Miyoshi, M., ”A new veriﬁcation methodof applied calibrations onto visibility data”,
in Proceedings of the 13th NICT TDC
Symposium, p. 3, Kashima, Japan, June
2014, http://www2.nict.go.jp/sts/stmg/
ivstdc/news 34/pdf/pctdc news34.pdf[2] Miyoshi, M., Shen, Z-Q., Oyama, T., Takahashi, R., Kato Y., Publ. Astron. Soc. Japan,
63, p1093-1116 (2011).
[3] Miyoshi, M., 2003, in Mass-losing pulsatingstars and their circumstellar matter. Workshop, May 13-16, 2002, Sendai, Japan, edited
by Y. Nakada, M. Honma and M. Seki. Astrophysics and Space Science Library, 283, Dordrecht: Kluwer Academic Publishers, p. 303 306

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

Figure 1. Examples of residual systemic errors found by the VERICA Methods: The cases of diﬀerential
amplitude distributions are from (a) to (d), and those of diﬀerential phase distributions are from (e) to(h). Cases of outliers with a large deviation are (a) and (e). Small vertical arrows indicate outliers.
Cases of none zero mean distributions are (b) and (f ) which distributions show oﬀsets towards left side
(minus direction) as shown by large arrows. The subsets of (c),(d),(g), and (h) show cases of multiple
peaks. Also, the subset (f ) shows double peaks. These three types of distributions cannot be explainedby only the natures of thermal noise, suggesting the existences of residual systematic errors in calibrated
data.

November 2016

25

Figure 2. Examples of diﬀerential visibility distributions of no signal data: The data are from the 43
GHz VLBA observations of SiO masers from VY CMa (BM099). In order to obtain emissions of thetwo maser lines (J=1-0 transitions at v=1 and v=2 states) simultaneously, they used two basebands.
We picked up velocity channels without maser emissions from the respective two basebands. The upper
three panels show histograms in 51-point bins of the distribution of diﬀerential visibility amplitude. The
arrows in the panels indicate that not a zero value bin exists at the position. The lower three panels show
histograms in 31-point bins of the distribution of diﬀerential visibility phase. The left two panels show
those from LA - PT baseline, the middle two from HN - OV baseline, and the left two from MK-SC
baseline. The IF (baseband) channels are between IF 1(sky frequency is 43.1GHz) and IF 2 (sky frequency
is 42.8 GHz). The optimized theoretical ﬁtting curve is shown by a solid line. The estimated noise levels
are from the least square ﬁtting to diﬀerential amplitude distributions (upper panels), The estimated
SNRs are from the least square ﬁtting to diﬀerential phase distributions (lower panels). The χ2 value ofthe ﬁtting, the number of diﬀerential visibility Ndata are shown in every panel. The diﬀerential visibility
distributions show oﬀsets from zero, and have outliers which suggesting the existences of systematic
errors in calibrated data.

IVS NICT-TDC News No.36

26

VLBI Direct Sampling Digital
Frontend
Kenichi Harada (harada@elecs.co.jp),
Yoshinori Hayashi, Kenji Ema,
Yuichi Chikahiro, Hirofumi Onuki,
and Kensuke Ozeki

 Data output• 1/10/40Gbit Ethernet• VTP / VDIF / UDP(TCP) / IP
• Jumbo frame

Elecs Industry Co.,LTd,
1-22-23 Shinsaku, Takatsu, Kawasaki, Kanagawa,
213-0014, Japan
Abstract: We devleloped GIGA SAMPLER and
PETA DATA RECORDER for radio astronomy
and geodesy. GIGA SAMPLER can directly sample S-band, X-band, and K-band RF analog signal
without the IF down converters. Direct sampling
eliminate some analog components and reduce system cost and size.
1.

Figure 1. Direct Sampler (integrate type)

GIGA SAMPLER<Features>• Wide variation of sampling module from
24Gsps x 3bit to 2Gsps x 12bit.

Figure 2. Block Diagram (integrate type)• Reduce system cost by RF/IF direct sampling
up to 24GHz. No need of frequency conversion.
• Signal processing for: Fourier transform, frequency conversion, ﬁlter, correlator, demodulation etc.
• FPGA signal processing can be developed byuser.
• You can choose integrate type or separate
type.

DSP + Output

ADC

Figure 3. Direct Sampler (separate type)• Optional web-base GUI software made possi- 2. Direct Sampling Benefits
ble the integrative control of signal analysis
solution, such as PETA DATA RECORDER 3. PETA DATA RECORDER
and GIGA SAMPLER, via web browser.
<Features><Speciﬁcations> ADC module• 2Gsps x 12bit BW 3GHz (Option BW
18GHz)• 4Gsps x 10bit BW 10GHz (Option BW
18GHz)• 24Gsps x 3bit BW 24GHz DSP module• Fourier transform with window function• Frequency conversion and ﬁlter (Digital
Baseband Converter)• Correlator ( auto / cross / delay compensation / fringe rotation / fractional delay[ΔW] )• User custom logic• Record high-speed and broadband data
stream input via 10/40/100G ethernet at maximum speed of 32Gbps.
• Removable storage is safety transported with
its own purpose-built carry case.
• The durability of the storage module connector is over 10,000 times of insert / remove.
• Realizing direct analysis of data stream without ﬁle format conversion by adopting Linux
ﬁle system for the storage.
• Optional web-base GUI software made possible the integrative control of signal analysis
solution, such as PETA DATA RECORDER
and GIGA SAMPLER, via web browser.
<Speciﬁcations> Record / Playback

November 2016

27

Antenna Cabin Digital Optical
Transmission

Observation RoomFigure 4. Block Diagram (separate type)Figure 5. Direct Sampling Beneﬁts• Maximum Record / Playback speed
32Gbps• RAID level 0 / 5 / 6• Linux XFS File system
 Storage• Maximum 4 removable storage modules• 12 HDD/SSD units per 1storage module• Secured transportation with the own
purpose-built carry case
 Data input / output

4.

Web-baes Integrate GUI Software<Features>• Web-base integrate GUI software (GIGA
SAMPLER , PETA DATA RECORDER ,etc.)• Don’t depend on OS and machine.
• Analyze recorded data ( spectrum, quantization bit distribution )• The control function of other company product can be supported by customization.

5. Delivery Achievement• 10/40/100Gbit Ethernet• Compatible with a wide variety of stream
 NAOJ (National Astronomical Observatory of
protocolJapan)• VERA (VLBI Exploration of Radio Astrometry)• Nobeyama Radio Observatory• Chile Observatory
 NICT (National Institute of Information andCommunications Technology)
Figure 6. PETA DATA RECORDER• Gala-V (Galapagos VLBI)• Yamagawa Solar Radio Observatory
 KASI (Korea Astronomy and Space Science
Institute)IVS NICT-TDC News No.36

28

Figure 7. Analysis of recorded data

Figure 8.
NICT

Gala-V Kashima,

Figure 9. KVN Yonsei, KASI

Figure 11. VERA Mizusawa, NAOJ
• KJCC (Korea-Japan Correlation Center)• KVN (Korean VLBI Network) Ibaraki University
 Yamaguchi University

Figure 10. Nobeyama, NAOJ

Figure 12. Yamagawa, NICT“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 biannually 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/sts/stmg/ivstdc/news-index.html”.

IVS NICT TECHNOLOGY DEVELOPMENT CENTER NEWS No.36, November 2016
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