KaVA Status Report for 2014B
KaVA User Support Team,NAOJ and KASI
April 25, 2014

1

Contents
1 Introduction

3

2 System

4

2.1

Array

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

2.2

Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5

2.2.1

Brief Summary of VERA Antennas . . . . . . . . . . . . . . . .

5

2.2.2

Brief Summary of KVN Antennas . . . . . . . . . . . . . . . . .

6

2.2.3

Aperture Efficiency . . . . . . . . . . . . . . . . . . . . . . . . .

6

2.2.4

Beam Pattern and Size . . . . . . . . . . . . . . . . . . . . . . .

7

Receivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9

2.3.1

Brief Summary of VERA Receiving System . . . . . . . . . . .

9

2.3.2

Brief Summary of KVN Receiving System . . . . . . . . . . . .

10

2.4

Digital Signal Process . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13

2.5

Recorders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13

2.6

Correlators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13

2.7

Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

14

2.7.1

Delay and Bandpass Calibration . . . . . . . . . . . . . . . . . .

14

2.7.2

Gain Calibration . . . . . . . . . . . . . . . . . . . . . . . . . .

14

Geodetic Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . .

15

2.8.1

Brief Summary of VERA Geodetic Measurement . . . . . . . .

15

2.8.2

Brief Summary of KVN Geodetic Measurement . . . . . . . . .

16

2.3

2.8

3 Observing Proposal

17

3.1

Call for Proposal (CfP) . . . . . . . . . . . . . . . . . . . . . . . . . . .

17

3.2

Proposal Submission . . . . . . . . . . . . . . . . . . . . . . . . . . . .

17

3.3

Observation Mode

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

17

3.4

Angular Resolution and Largest Detectable Angular Scale . . . . . . .

18

3.5

Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

18

3.6

Calibrator Information . . . . . . . . . . . . . . . . . . . . . . . . . . .

19

3.7

Date Archive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

20

4 Observation and Data Reduction

21

4.1

Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

21

4.2

Observation and Correlation . . . . . . . . . . . . . . . . . . . . . . . .

21

4.3

Data Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

21

4.4

Further Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

21

2

1

Introduction

This document summarizes the current observational capabilities of KaVA (KVN and
VERA Array), which is a combined VLBI network of KVN (Korean VLBI Network)
and VERA (VLBI Exploration of Radio Astrometry) operated by Korea Astronomy
and Space Science Institute (KASI) and National Astronomical Observatory of Japan(NAOJ), respectively (see Figure 1). In 2014, KaVA system is still being developedand some capabilities are remained to be implemented.
KaVA invites proposals for the second common use observations to be carried out
from September 1, 2014 to January 15, 2015 (2014B). This call for proposals (CfP) is
offered for open use in a shared-risk mode.

Mizusawa
Yonsei

Ulsan

Tamna
Iriki

Ogasawara
Ishigakijima

Figure 1: Array configuration of KaVA.
VERA is a Japanese VLBI array to explore the 3-dimensional structure of the Milky
Way Galaxy based on high-precision astrometry of Galactic maser sources. VERA array consists of four 20 m radio telescopes located at Mizusawa, Iriki, Ogasawara, andIshigakijima with baseline ranges from 1000 km to 2300 km. The construction of VERA
array was completed in 2002, and it is under regular operation since the fall of 2003.
VERA was opened to international users in the K band (22 GHz) and Q band (43 GHz)
from 2009. Most unique aspect of VERA is “dual-beam” telescope, which can simultaneously observe nearby two sources. While single-beam VLBI significantly suffers fromfluctuation of atmosphere, dual-beam observations with VERA effectively cancel out
the atmospheric fluctuations, and then VERA can measure relative positions of target sources to reference sources with higher accuracy based on the ‘phase-referencing’technique. For more detail, visit the following web site:
http://veraserver.mtk.nao.ac.jp/index.html.
KVN is the mm-wavelength VLBI facility in Korea. It consists of three 21 m radio
telescopes, which are located in Seoul (Yonsei University), Ulsan (University of Ulsan),and Jeju island (ex-Tamna University), and produces an effective spatial resolution3

equivalent to that of an 500 km radio telescope. KASI has developed innovative multifrequency band receiver systems, observing four different frequencies at 22, 43, 86,
and 129 GHz simultaneously. With this capability, KVN will provide opportunities tostudy the formation and death processes of stars, the structure and dynamics of ourown Galaxy, the nature of Active Galactic Nuclei and so on at milli-arcsecond (mas)resolutions. For more detail, visit the following web site and paper (Lee et al. 2011):
http://kvn-web.kasi.re.kr/eng.
KaVA was formed in 2010, on the basis of the VLBI collaboration agreement between
KASI and NAOJ. KaVA complements baseline length range up to 2270 km, and canachieve a good imaging quality. Currently, KaVA supports observations at K band andQ band in left-hand-circular polarization with a data aggregation rate of 1024 Mega bit
per seconds (bps) (=1 Gbps). This document is intended to give astronomers necessary
information for proposing observations with KaVA.

2

System

2.1

Array

KaVA consists of 7 antenna sites in VERA-Mizusawa, VERA-Iriki, VERA-Ogasawara,
VERA-Ishigakijima, KVN-Yonsei, KVN-Ulsan and KVN-Tamna with 21 baselines (seeFigure 1). The maximum baseline length is 2270 km between Mizusawa and Ishigakijima, and the minimum baseline length is 305 km between Yonsei and Ulsan. The
maximum angular resolution expected from the baseline length is about 1.2 mas forK band and about 0.6 mas for Q band. The geographic locations and coordinate of each
KaVA antenna in the coordinate system of epoch 2009.0 are summarized in Table 1.
Figure 2 shows examples of uv plane coverage.

Figure 2: The uv plane coverage (±3000 km) expected with KaVA antennas from an
observation over elevation of 20◦ . Each panel shows the uv coverage for the declinationof 60◦ (left), 20◦ (center ), and –20◦ (right).
The average velocities of VERA stations in Table 2 are predicted value at the epochof 01/Oct/2011. Reference frame of these coordinates is ITRF2008. The rates of
the coordinates of Mizusawa are the average value of change of the coordinates in
September, 2011. The rates of the coordinates of Iriki, Ogasawara and Ishigakijima
are obtained from averaging of change of the coordinates from December, 2004 to4

February, 2011. The 2011 off the Pacific coast of Tohoku Earthquake (Mj=9.0) brought
the co-seismic large step and non-linear post-seismic movement to the coordinates ofMizusawa. Co-seismic steps of the coordinates of Mizusawa are dX=-2.0136 m, dY=1.3795 m and dZ=-1.0721 m. The creeping continues still now, though decreased. Thechanges of coordinates by the post-seismic creeping are dX=-0.7269 m, dY=-0.5020 m
and dZ=-0.2017 m in total from March 12, 2011 to October 1, 2013. Post seismic
movements of Mizusawa are very complex. Internal error of coordinates of Mizusawa
by polynomial fitting is 5-6mm. But, in a solution, a several centimeter differences
arise for every fitting with the increase in geodetic observation data. It is judged thatthese differences are the uncertainly of the coordinates of Mizusawa.
Table 1: Geographic locations and motions of each KaVA antenna.
East
North
Longitude
LatitudeSite[◦ ′ ′′ ][◦ ′ ′′ ]Mizusawa
141 07 57.3 39 08 00.7
Iriki
130 26 23.6 31 44 52.4
Ogasawara
142 12 59.8 27 05 30.5
Ishigakijima 124 10 15.6 24 24 43.8
Yonsei∗
126 56 27.4 37 33 54.9
Ulsan∗
129 14 59.3 35 32 44.2
Tamna∗
126 27 34.4 33 17 20.9∗
: KVN GPS measurements.

Ellipsoidal
Height
[m]
116.4
573.6
273.1
65.1
139
170
452

X
[m]
–3857244.4029–3521719.7674–4491068.6055–3263994.0413–3042280.9137–3287268.6186–3171731.5580

Y[m]3108783.1553
4132174.6548
3481545.0506
4808056.3278
4045902.7164
4023450.1799
4292678.4878

Z[m]
4003899.2638
3336994.1511
2887399.6815
2619948.8728
3867374.3544
3687380.0198
3481038.7252

Table 2: Station code and average velocity of each VERA antenna.
Site
IVS2a
IVS8b
CDPc ∆X [m/yr]d ∆Y [m/yr]d ∆Z [m/yr]dMizusawa
Vm
VERAMZSW 7362
–0.1096–0.0891–0.0354
Iriki
Vr
VERAIRIK
7364–0.0210–0.0087–0.0156
OgasawaraVo
VERAOGSW 7363
0.02520.02500.0094Ishigakijima
Vs
VERAISGK
7365–0.0348–0.0057–0.0540a
IVS 2-characters codeb
IVS 8-characters codec
CDP (NASA Crustal Dynamics Project) coded
The epoch of the coordinates is January 01, 2013. Average speed was obtained
from the VLBI data from September 27, 2012 to August 11, 2013.

In the case of KVN, all antenna locations are measured with GPS system. The
antenna positions of KVN are regularly monitored both with GPS system and geodetic
VLBI observations in collaboration with VERA. No velocity information is available
for KVN stations.

2.2

Antennas

2.2.1

Brief Summary of VERA Antennas

All the telescopes of VERA have the same design, being a Cassegrain-type antenna on
AZ-EL mount. Each telescope has a 20 m diameter dish with a focal length of 6 m,with a sub-reflector of 2.6 m diameter. The dual-beam receiver systems are installed at
the Cassegrain focus. Two receivers are set up on the Stewart-mount platforms, which
are sustained by steerable six arms, and with such systems one can simultaneously
5observe two adjacent objects with a separation angle between 0.32 and 2.2 deg. The
whole receiver systems are set up on the field rotator (FR), and the FR rotate to track
the apparent motion of objects due to the earth rotation. Table 3 summarizes theranges of elevation (EL), azimuth (AZ) and field rotator angle (FR) with their driving
speeds and accelerations. In the case of single beam observing mode, one of two beams
is placed at the antenna vertex (separation offset of 0 deg).
2.2.2

Brief Summary of KVN Antennas

The KVN antennas are also designed to be a shaped-Cassegrain-type antenna with an
AZ-EL mount. The telescope has a 21 m diameter main reflector with a focal length of
6.78 m. The main reflector consists of 200 aluminum panels with a manufacturing surface accuracy of about 65 µm. The slewing speed of the main reflector is 3 ◦ /sec, whichenables fast position-switching observations (Table 3). The sub-reflector position, tilt,
and tip are remotely controlled and modeled to compensate for the gravitational deformation of the main reflector and for the sagging-down of the sub-reflector itself.
Table 3: Driving performance of KaVA antennas.
Driving axis

Driving range

Max. driving speed Max. driving acceleration
VERA
AZa−90◦ ∼450◦
2.1◦ /sec
2.1◦ /sec2
◦
◦
◦
EL
5 ∼85
2.1 /sec
2.1◦ /sec2
b
◦
◦
◦
FR
−270 ∼270
3.1 /sec
3.1◦ /sec2
KVN
AZa−90◦ ∼450◦
3◦ /sec3◦ /sec2
◦
◦
◦
EL
5 ∼85
3 /sec3◦ /sec2a◦◦
The north is 0 and the east is 90 .
b
FR is 0◦ when Beam-1 is at the sky side and Beam-2 is at the ground side,
and CW is positive when an antenna is seen from a target source.

Table 4: Aperture efficiency and beam size of KaVA antennas.
Antenna Name
Mizusawa
Iriki
Ogasawara
Ishigakijima
Yonsei
Ulsan
Tamna

2.2.3

K band (22 GHz)
ηA
HPBW
(%)
(arcsec)
44
146
47
142
48
143
41
138
55
119
60
120
59
123

Q band (43 GHz)
ηA
HPBW
(%)
(arcsec)
51
76
41
73
46
74
42
75
60
62
56
62
62
62

Aperture Efficiency

The aperture efficiency of each VERA antenna is about 40–50% in both K band andQ band (see Table 4 for the 2012 data). These measurements were based on theobservations of Jupiter assuming that the brightness temperature of Jupiter is 160 K
in both the K band and the Q band. Due to the bad weather condition in someof the sessions, the measured efficiencies show large scatter. However, we conclude
6

that the aperture efficiencies are not significantly changed compared with previous
measurements. The elevation dependence of aperture efficiency for VERA antenna
was also measured from the observation toward maser sources. Figures 3 shows therelations between the elevation and the aperture efficiency measured for VERA Iriki
station. The gain curves are measured by observing the total power spectra of intense
maser sources. The aperture efficiency in low elevation of ≤ 20 deg decreases slightly,
but this decrease is less than about 10%. Concerning this elevation dependence, theobserving data FITS file include a gain curve table (GC table), which is AIPS readable,
in order to calibrate the dependence when the data reduction.
The aperture efficiency and beam size for each KVN antenna are also listed inTable 4. Aperture efficiency of KVN varies with elevation as shown in Figure 3. The
main reflector panels of KVN antennas were installed to give the maximum gain at
the elevation angle of 48◦ . The sagging of sub-reflector and the deformation of mainreflector by gravity with elevation results in degradation of antenna aperture efficiency
with elevation. In order to compensate this effect, KVN antennas use a hexapod toadjust sub-reflector position. Figure 3 shows the elevation dependence of antenna
aperture efficiency of the KVN 21 m radio telescopes measured by observing Venus or
Jupiter. By fitting a second order polynomial to the data and normalizing the fitted
function with its maximum, we derived a normalized gain curve which has the following
form:
Gnorm = A0 EL2 + A1 EL + A2 ,(1)
where EL is the elevation in degree.

Normarized Gain

Normarized Gain

KVNUS : Jupiter 2013-01-17

K-band

10

20

30

40

50

60

70

80

10

20

30

40

50
Elevation

60

70

80

Q-bandElevation

VERAIRIK : Jupiter
Normarized Gain

Normarized Gain

1.2

K-band2005-02-08 K-band

1.0
0.8
1.4

0

10

20

30

40

50

60

70

80

90

30

40

50

60

70

80

90

2005-02-12 Q-band

1.2
1.0
0.8
0.6

Q-band0

1020

Elevation

Elevation

Figure 3: The elevation dependence of the aperture efficiency for KVN three antennas
and VERA Iriki antenna. For KVN antennas, the maximum gain is given at theelevation angle of 48◦ . The efficiency in K-band (on Feb 8, 2005) and the Q-band(on Feb 12, 2005) for VERA Iriki antenna is shown in bottom right. The efficiency isrelative value to the measurement at EL = 50◦ .

2.2.4

Beam Pattern and Size

Figure 4 show the beam patterns in the K band. The side-lobe level is less thanabout −15 dB, except for the relatively high side-lobe level of about −10 dB for the7separation angle of 2.0 deg at Ogasawara station. The side-lobe of the beam patterns
has an asymmetric shape, but the main beam has a symmetric Gaussian shape without
dependence on separation angle. The measured beam sizes (HPBW) in the K bandand the Q band based on the data of the pointing calibration are also summarized inTable 4. The main beam sizes show no dependence on the dual-beam separation angle.
The optics of KVN antenna is a shaped Cassegrain type of which the main reflector
and subreflector are shaped to have a uniform illumination pattern on an apertureplane. Because of the uniform illumination, KVN antennas can get higher aperture
efficiency than value of typical Cassegrain type antenna. However, higher side-lobe levelis inevitable. OTF images of Jupiter at K and Q bands are shown in Figure 4. The
map size is 12’×10’ and the first side-lobe pattern is clearly visible. Typical side-lobelevels of KVN antennas are 13-14dB.
K-band Beam-A (SA : 0.0 deg) VERAIRIK

K-band Beam-A (SA : 2.0 deg) VERAOGSWPLot file version 1 created 12-SEP-2003 00:37:55
W49N 8.0 KM/S O280905.MAP-IT.1

400

400

300

300

200

200

100

100
ARC SEC

ARC SEC

PLot file version 1 created 07-AUG-2003 18:54:17
CONT: W49N 8.0 KM/S BEAM2.MAP-IT.2

0

0

-100

-100

-200

-200

-300

-300

-400

-400

400
300
200
100
0
-100
ARC SEC
Center at RA 19 10 13.476 DEC 09 06 14.29
Cont peak flux = 1.5787E+04 K km/s
Levs = 1.579E+02 * (0.100, 0.300, 0.500, 1, 3, 5,
10, 30, 50, 100)

-200

-300

-400

400
300
200
100
0
-100
ARC SEC
Center at RA 19 10 13.476 DEC 09 06 14.29
Peak flux = 6.3418E+03 K km/s
Levs = 6.342E+01 * (0.100, 0.300, 0.500, 1, 3, 5,
10, 30, 50, 100)

-500

-200

-300

-400

Q-band Jupiter KVN Yonsei

K-band Jupiter KVN Yonsei

Figure 4: The beam patterns in the K-band for VERA (A-beam) Iriki with the separation angle of 0◦ (Upper left) and Ogasawara with the separation angle of 2.0◦ (Upperright), and in K/Q-band for KVN Yonsei. The patterns of VERA antennas were derived from the mapping observation of strong H2 O maser toward W49N, which can beassumed as a point source, with grid spacing of 75′′ . In the case of KVN antennas, thepatterns were derived from the OTF images of Venus at K/Q-band.

8

2.3

Receivers

2.3.1

Brief Summary of VERA Receiving System

Each VERA antenna has the receivers for 4 bands, which are S (2 GHz), C (6.7 GHz),X (8 GHz), K (22 GHz), and Q (43 GHz) bands. For the common use in 2009, theK band and the Q band are open for observing. The low-noise HEMT amplifiers in the
K and Q bands are enclosed in the cryogenic dewar, which is cooled down to 20 K, toreduce the thermal noise. The range of observable frequency and the typical receivernoise temperature (TRX ) at each band are summarized in the Table 5 and Figure 5.
Table 5: Frequency range and TRX of VERA and KVN receivers.
TRX a
[K]

Polarization

30-50
70-90

LCP
LCP

Frequency Range
[GHz]

Band

VERA
K
Q

21.5-23.8
42.5-44.5
KVN

K
Q

30-40
70-80
(40-50 for Ulsan)aReceiver noise temperature

60.0

Trx [K]

50.0

21.25-23.25
42.11-44.11

LCP/RCPLCP/RCPK-band

MIZ
IRK
OGA
ISG

40.0
30.0
20.0
10.0
0.0
4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

fIF [GHz]

120.0

Trx [K]

100.0

Q-band

MIZ
IRK
OGA
ISG

80.0
60.0
40.0
20.0
0.0
4.0

5.0

6.0

7.0

8.0

fIF [GHz]

Figure 5: Receiver noise temperature for each VERA antenna. Top and bottom panels
show measurements in the K and Q bands, respectively. Horizontal axis indicate an
IF (intermediate frequency) at which TRX is measured. To convert it to RF (radio
frequency), add 16.8 GHz in the K band and 37.5 GHz in the Q band to the IF
frequency.

9After the radio frequency (RF) signals from astronomical objects are amplified by
the receivers, the RF signals are mixed with standard frequency signal generated in
the first local oscillator to down-convert the RF to an intermediate frequency (IF) of
4.7 GHz–7 GHz. The first local frequencies are fixed at 16.8 GHz in the K band andat 37.5 GHz in the Q band. The IF signals are then mixed down again to the baseband frequency of 0–512 MHz. The frequency of second local oscillator is tunablewith a possible frequency range between 4 GHz and 7 GHz. The correction of the
Doppler effect due to the earth rotation is carried out in the correlation process after
the observation. Therefore, basically the second local oscillator frequency is kept to
be constant during the observation. Figure 6 shows a flow diagram of these signals for
VERA.
K: 21.5 - 23.8 GHz
Q: 42.5 - 44.5 GHz
IF: 4.7 - 7 GHz

Base Band:
0 - 512 MHz

1st Local
K: 16.8 GHz
Q: 37.5 GHz

2nd Local
4 - 7 GHz

RecorderDigital Filter

A/D Converter

Receiver #1

Receiver #2

Figure 6: Flow diagram of signals from receiver to recorder for VERA.

2.3.2

Brief Summary of KVN Receiving System

The KVN quasi-optics are uniquely designed to observe 22, 43, 86 and 129 GHz band
simultaneously (Han et al. 2008, 2013). Figure 7 shows the layout of quasi-optics andreceivers viewing from sub-reflector side. The quasi-optics system splits one signal fromsub-reflector into four using three dichroic low-pass filters marked as LPF1, LPF2 andLPF3 in the Figure 7. The split signals into four different frequency bands are guided
to corresponding receivers.
Figures 8 shows a signal flows in KVN system. The 22, 43 and 86 GHz band receivers
are cooled HEMT receivers and the 129 GHz band receiver is a SIS mixer receiver. All
receivers receive dual-circular-polarization signals. Among eight signals (four dualpolarization signals), four signals selected by the IF selector are down-converted tothe input frequency band of the sampler. The instantaneous bandwidth of the 1st
IF of each receiver is limited to 2 GHz by the band-pass filter. The 1st IF signal isdown-converted by BBCs to the sampler input frequency (512-1024 MHz) band.
Typical noise temperatures of K and Q bands are presented in Table 5. Since thecalibration chopper is located before the quasi-optics as shown in Figure 7, the lossof quasi-optics contributes to receiver noise temperature instead of degrading antenna
aperture efficiency. Therefore, the noise temperature in the table includes the contribution due to the quasi-optics losses.
The receiver noise temperatures of three stations are similar to each other exceptthat the noise temperature of the Ulsan 43 GHz because of the different type of thermal

10isolator, which is used to reduce heat flow from the feed horn in room temperature stage
to cryogenic cooled stage more effectively.

Figure 7: KVN multi-frequency receiving system (Han et al. 2008, 2013).

Figure 8: Flow diagram of signals from receiver to recorder for KVN (Oh et al. 2011).

11

Table 6: Digital filter mode for KaVA.
Freq. ranged
Side
CH
(MHz)
Bande Notef
1
0 - 16U
2
32 - 48U
3
64 - 80U496 - 112U
5
128 - 144U
6
160 - 176U
7
192 - 208U8
224 - 240U
9
256 - 272
U
Target line (e.g. H2 O)
10
288 - 304U11
320 - 336U
12
352 - 368U
13
384 - 400U
14416 - 432U15
448 - 464U
16
480 - 496
U
GEO1S∗
1024
16
16
1
112 - 128L2
128 - 144U
3
144 - 160L4
160 - 176U
5
176 - 192L6
192 - 208U
7
208 - 224L8
224 - 240U
9
240 - 256L10
256 - 272
U
Target line (e.g. H2 O)
11
272 - 288L
12
288 - 304U
13
304 - 320L14
320 - 336U
15
336 - 352L
16
352 - 368
U
VERA7SIOS∗
1024
16
16
1
32 - 48U
2
64 - 80U
3
80 - 96
L
SiO (J=1-0, v=2)4
96 - 112U
5
128 - 144U
6
160 - 176U
7
192 - 208U8
224 - 240U
9
256 - 272U
10
288 - 304U11
384 - 400U
SiO (J=1-0, v=1)
12
320 - 336U
13
352 - 368U
14
416 - 432U15
448 - 464U
16
480 - 496
U∗
All channels are for A-Beam (VERA) and LCP (VERA/KVN). Mode names are tentative.
aTotal number of channelsbBandwidth per channel in MHzcChannel numberdFiltered frequency range in the base band (MHz)e
Side Band (LSB/USB)f
Example of spectral line setting

Mode
Name
GEO1K∗

Rate(Mbps)
1024

Num.
CHa
16

BW/CHb
(MHz)
16

c

12

2.4

Digital Signal Process

In VERA system, A/D (analog-digital) samplers convert the analog base band outputs
of 0–512 MHz ×2 beams to digital form. The A/D converters carry out the digitizationof 2-bit sampling with the bandwidth of 512 MHz and the data rate is 2048 Mbps foreach beam.
In KVN system, A/D samplers digitize signals into 2-bit data streams with four
quantization levels. The base band output is 512–1024 MHz. The sampling rate is 1024
Mega sample per second (Msps) with 2-bit sampling resulting a 2048 Mbps=2 Gbps
data rate at 512 MHz frequency bandwidth. Four streams of 512 MHz band width(2 Gbps data rate) can be obtained in the KVN multi-frequency receiving systemsimultaneously, which means that the total rate is 8 Gbps.
Since the total data recording rate is limited to 1024 Mbps (see the next section),
only part of the sampled data can be recorded onto magnetic tape. The data rate
reduction is done by digital filter system, with which one can flexibly choose number
and width of recording frequency bands. Observers can select modes of the digital
filter listed in the Table 6. For the 2014B KaVA observing season, three digital filter
modes are available. In VERA7SIOS (TBD) mode in the Table 6, two transitions(v=1 & 2) of SiO maser in the Q band can be simultaneously recorded. For the
DIR-100M system, any two CH in GEO1K, GEO1S, and VERA7SIOS modes can be
simultaneously recorded.

2.5

Recorders

The KaVA observations are basically limited to record with 1024 Mbps=1 Gbps data
rate. To response 1 Gbps recording, VERA and KVN have a DIR-2000 and Mark5B
recording system, respectively. DIR-2000 is a high speed magnetic tape recorder, andMark5B is a hard disk recording system developed at Haystack observatory. Their
total bandwidths are 256 MHz because of 2-bit sampling. The recording time per rollof tape are 80 mins in the DIR-2000 system. In the case of the Mark5B system, therecording time depends on data size of disk-pack(e.g. 4TB,8TB,16TB,24TB).

2.6

Correlators

The correlation process is carried out by a VLBI correlator located at KJCC (KoreaJapan Correlation Center) at Daejeon, which has been developed as the KJJVC (KoreaJapan Joint VLBI Correlator) located at KJCC (Korea-Japan Correlation Center)
project. Hereafter it is tentatively called ”Daejeon correlator”. The Daejeon correlator
can process the data stream of up to 8192 Mbps from maximum 16 antenna stations at
once. Currently the raw observed data of KVN stations are recorded and playbacked
with Mark5B, and those of VERA stations are recorded and playbacked with DIR2000(VERA-2000) at the data rate of 1024 Mbps. The only data format available in
the next observing season is 16 IFs×16 MHz (”C5 mode” in The Daejeon correlator
terminology). Minimum integration time (time resolution) is 1.6384 seconds at thismode, and the number of frequency channels within each IF is 8192 (i.e. maximum
frequency resolution is about 1.95 kHz). By default, the number of frequency channels
is reduced to 128 (for continuum) or 512 (for line) via channel integration after correlation. One may put a special request of number of frequency channels to take better13

frequency resolution. The number of frequency channels can be selected among 512,
1024, 2048, 4096 or 8192. Final correlated data is served as FITS-IDI file.
Specification of The Daejeon correlator is summarized in Table 7.
Table 7: Specification of The Daejeon correlatora .
Max. number of antennas
16
correlation mode
C5(16 MHz Bandwidth, 16 stream)Max. number of corr./input 120 cross + 16 auto
Sub-array
2 case(12+4, 8+8)
Bandwidth
512 MHzMax. data rate/antenna2048 Mbps VSI-H(32 parallels, 64MHz clock)Max. delay compensation± 36,000 km
Max. fringe tracking
1.075 kHzFFT work length
16+16 bits fixed point for real, imaginary
Integration time
25.6 msec ∼ 10.24 sec
Data output channels
8192 channels
Data output rate
Max. 1.4GB/sec at 25.6msec integration timea
For more details, see
http://kvn.kasi.re.kr/status_report/correlator_status.html.

2.7

Calibration

Here we briefly summarize the calibration procedure of the KaVA data. Basically, mostof the post-processing calibrations are done by using the AIPS (Astronomical Image
Processing System) software package developed by NRAO (National Radio Astronomical Observatory).
2.7.1

Delay and Bandpass Calibration

The time synchronization for each antenna is kept within 0.1 µsec using GPS andhigh stability frequency standard provided by the hydrogen maser. To correct for
clock parameter offsets with better accuracy, bright continuum sources with accuratelyknown positions should be observed at usually every 60–80 minutes during observations.
A recommended scan length for calibrators is 5–10 minutes. This can be done by the
AIPS task FRING. The calibration of frequency characteristic (bandpass calibration)
can be also done based on the observation of bright continuum source. This can bedone by the AIPS task BPASS.
2.7.2

Gain Calibration

Both VERA and KVN antennas have the chopper wheel of the hot load (black body at
the room temperature), and the system noise temperature can be obtained by measuring the ratio of the sky power to the hot load power (so-called R-Sky method). Thus,
the measured system noise temperature is a sum of the receiver noise temperature,∗spillover temperature, and contribution of the atmosphere (i.e. so-called Tsyscorrected
for atmospheric opacity). The hot load measurement can be made before/after any
scan. Also, the sky power is continuously monitored during scans, so that one cantrace the variation of the system noise temperature. The system noise temperature
value can be converted to SEFD (System Equivalent Flux Density) by dividing by
14

the antenna gain in K/Jy, which is derived from the aperture efficiency and diameterof each antenna. Using the SEFD values, the visibility amplitude in unit of Jy canbe obtained by the AIPS task APCAL. Alternatively, one can calibrate the visibility
amplitude by the template spectrum method, in which auto-correlation spectra of amaser source is used as the flux calibrator. This calibration procedure is made by the
AIPS task ACFIT (see AIPS HELP for ACFIT for more detail).
Further correction is made for VLBI observations taken with 2-bit (4-level) sampling,
for the systematic effects of non-optimal setting of the quantizer voltage thresholds.
This is done by the AIPS task ACCOR. The amplitude calibrations with KaVA are
accurate to 15% or better at K and Q bands.

2.8

Geodetic Measurement

2.8.1

Brief Summary of VERA Geodetic Measurement

Geodetic observations are performed as part of the VERA project observations toderive accurate antenna coordinates. The geodetic VLBI observations for VERA are
carried out in the S/X bands and also in the K band. The S/X bands are used in
the domestic experiments with the Geographical Survey Institute of Japan and theinternational experiments called IVS-T2. On the other hand, the K band is used inthe VERA internal experiments. We obtain higher accuracy results in the K band
compared with the S/X bands. The most up-to-date geodetic parameters are derived
through geodetic analyses.
Non-linear post seismic movement of Mizusawa after the 2011 off the Pacific coast of
Tohoku Earthquake continues. The position and velocity of Mizusawa is continuously
monitored by GPS. The coordinates in the Table 1 are provisional and will be revisedwith accumulation of geodetic data by GPS and VLBI.
In order to maintain the antenna position accuracy, the VERA project has threekinds of geodetic observations. The first is participation in JADE (JApanese Dynamic
Earth observation by VLBI) organized by GSI (Geographical Survey Institute) and
IVS-T2 session in order to link the VERA coordinates to the ITRF2008 (International
Terrestrial Reference Frame 2008). Basically Mizusawa station participates in JADE
nearly every month. Based on the observations for four years, the 3-dimensional positions and velocities of Mizusawa station till 09/Mar/2011 is determined with accuraciesof 7-9 mm and about 1 mm/yr in ITRF2008 coordinate system. But the uncertainty
of several centimeters exists in the position on and after March 11, 2011. The second
kind of geodetic observations is monitoring of baseline vectors between VERA stations
by internal geodetic VLBI observations. Geodetic positions of VERA antennas relativeto Mizusawa antenna are measured from geodetic VLBI observations every two weeks.
From polygonal fitting of the six-year geodetic results, the relative positions and velocities are obtained at the precisions of 1-2 mm and 0.8-1 mm/yr till 10/Mar/2011. The
third kind is continuous GPS observations at the VERA sites for interpolating VLBI
geodetic positions. Daily positions can be determined from 24 hour GPS data. The
GPS observations are also used to estimate tropospheric zenith delay of each VERA
site routinely. The time resolution of delay estimates is 5 minutes.

15

2.8.2

Brief Summary of KVN Geodetic Measurement

KVN antenna positions are measured by using GPS antennas (Figure 9). Two GPS
antennas were installed at both sides of elevation gears and measured their positions
for a day. Locations of receiver were determined, and then the invariant point (IVP)
was calculated using those two GPS antenna positions and their offsets from the IVP.
The accuracy of GPS measurement is approximately about 5 cm.
In order to improve and maintain accurate antenna positions, KVN antenna positions are regularly monitored using GPS and geodetic VLBI observations. The K band
geodesy VLBI program between KVN and VERA has been started in 2011 (see Table 8). The typical 1-sigma errors of geodetic solutions are about 0.4 cm in X, Y, andZ directions for a successful measurement. However, the geodetic VLBI solutions were
not applied to KVN antenna positions until more measurements are obtained.
Table 8: The status of KaVA K band geodesy observations.
Obs. Code Obs. Date
AntennaNoter11333k2011 Nov. 29 Ky Ku Kt Vm Vr Vs Vo VERA+Yonsei solution was obtained
r11361k2011 Dec. 27 Ky Kt Vm Vr Vs Vo
Observation failed
r12271k2012 Sep. 27 Ky Ku Kt Vm Vr Vs Vo All solutions were obtained
r13088k2013 Mar. 29 Ky Ku Kt Vm Vr Vs Vo All solutions were obtained
r13140k2013 May 20 Ky Ku Kt Vm Vr Vs Vo All solutions were obtained
r13251k2013 Sep. 9
Ky Ku Kt Vm Vr Vs Vo in progress
r13313k2013 Nov. 9
Ky Ku Kt Vm Vr Vs Vo in progress
r14028k2014 Jan. 28 Ky Ku Kt Vm Vr Vs Vo in progressr14095k2014 Apr. 5
Ky Ku Kt Vm Vr Vs Vo in progress
Ky, Ku, and Kt stand for Yonsei, Ulsan, and Tamna antennas in KVN, respectively.
Vm, Vr, Vs, and Vo represent Mizusawa, Iriki, Ishigakijima, and Ogasawara antennas in VERA,
respectively.

Figure 9: IVP determination of KVN antennas using two GPS antennas.

16

3

Observing Proposal

3.1

Call for Proposal (CfP)

For the second KaVA observing season from September 2014 to January 2015 (2014B),
three 21 m KVN antennas and four 20 m VERA antennas are opened for singlefrequency single-polarization (LCP) observations at K and Q bands. Recording rateof 1024 Mbps=1 Gbps (total bandwidth of 256 MHz) will be open for the 2014B CfP.
Correlation of the KaVA data will be done by The Daejeon correlator at KJCC. Total
observing time up to 260 hours will be available for the common-use observing timefor KaVA in the 2014B period. The application must be received by
08:00 UTC on June 16, 2014
for the 2014B CfP. Proposals of which principal investigator (PI) belongs to the Korean
and Japanese institutes/universities can be accepted for the 2014B CfP, but proposers
are not required to include collaborators from KVN/VERA projects as a co-investigator(CoI). Note that the KaVA observing sessions in 2014B will be carried out as risk-shared
open use.

3.2

Proposal Submission

As for the proposal submission, details and application forms of KaVA proposal canbe found at the KaVA CfP web site:
http://veraserver.mtk.nao.ac.jp/restricted/KaVA2014B.html.
Any questions on proposal submission should be sent to kavaprop@kasi.re.kr. If
an applicant wants to have a collaborator from the KVN and VERA group member
for extensive support, the KaVA User Support Team (UST) will be able to arrange acollaborator (support scientist), after the acceptance of proposal.
Proposals submitted for the 2014B CfP will be reviewed by the referees consistedof KVN and VERA referees already assigned to each array. KaVA makes technicalreview of all the proposals. The KVN Time Allocation Committee (TAC) and VERAProgram Committee (PC) make rating of each KaVA proposal based on the referees,
and the KaVA Combined TAC (CTAC) decide the allocation based on each rating
result. The results of the review will be announced to PIs in middle of July 2014.

3.3

Observation Mode

The K band and the Q band single-frequency single-polarization modes are available
and a recording rate of 1024 Mbps (total bandwidth of 256 MHz) will be open for the
2014B CfP. Dual-beam mode with VERA, dual-polarization with KVN, and simultaneous multi-frequency mode with KVN will not be available for the 2014B CfP. For accurate astrometric observations, many items (antenna positions, calibrators, schedule,etc.) should be carefully considered and prepared. At present, astrometric VLBI observations with KaVA is not supported in the 2014B CfP. Moreover, phase-referencing
based on antenna-fast nodding with VERA and KVN has not yet been available in the
2014B CfP, since the feasibility of the phase-referencing observation including scheduling, recording, and correlation, should be fully verified.
17

3.4

Angular Resolution and Largest Detectable Angular Scale

The expected angular resolutions for the K band and the Q band are about 1.2 mas and
0.6 mas, respectively. The synthesized beam size strongly depends on UV coverage,
and could be higher than the values mentioned above because the baselines projected
on UV plane become shorter than the distance between antennas. The beam size canbe calculated approximately by the following formula;λθ ∼ 2063
[cm]

!

B
[km]

!−1

[mas].

(2)

where λ and B are observed wavelength in centimeter and the maximum baseline length
in kilometer, respectively.
The minimum detectable angular scale for interferometers can be also expressed byequation (2), where the baseline length B is replaced with the shortest one among thearray. Because of the relatively short baselines provided by KVN, ∼300 km, KaVA isable to detect an extended structure up to 9 mas and 5 mas for the K and Q bands,
respectively.

3.5

Sensitivity

When a target source is observed, a noise level σbl for each baseline can be expressedasqqTsys,1 Tsys,22k
1 SEF Dsys,1 SEF Dsys,2
√
√
σbl =
=
,
(3)
√
η Ae1 Ae2 2Bτη
2Bτwhere k is Boltzmann constant, η is quantization efficiency (∼ 0.88), Tsys is system
noise temperature, SEF D is system equivalent flux density, Ae is antenna effective
aperture area (Ae = πηA D2 /4 in which Ae and D are the aperture efficiency andantenna diameter, respectively), B is the bandwidth, and τ is on-source integration
time. Note that for an integration time beyond 3 minutes (in the K band), the noiselevel expected by equation (3) cannot be attained because of the coherence loss dueto the atmospheric fluctuation. Thus, for finding fringe within a coherence time, theintegration time τ cannot be longer than 3 minutes. For VLBI observations, signal-tonoise ratio (S/N ) of at least 5 and usually 7 is generally required for finding fringes.
A resultant image noise level σim can be expressed asσim = q

1
−2
Σσbl

.

(4)

If the array consists of identical antennas, an image noise levels can be expressed as
σbl =

2k
Tsys
SEF D
1
q
= q
,
η Ae N (N − 1)Bτ
η N (N − 1)Bτ

(5)where N is the number of antennas. Using the typical antenna parameters (Table 9),baseline and image sensitivity values of KaVA are calculated as listed in Table 10.
Figures 10 and 11 show the system noise temperature at Mizusawa and Ulsan,
respectively. For Mizusawa, receiver noise temperatures are also plotted.
18

Band
K
Q

Table 9: Parameters of each antenna.
KVN
VERA
Tsys[K] ηA SEFD [Jy]Tsys[K] ηA SEFD [Jy]
100
0.6
1328
120
0.5
2343
150
0.6
1992
250
0.5
4881

Table 10: Sensitivity of each array.
Baseline sensitivity [mJy]
Image sensitivity [mJy]Band VERA-VERA KVN-KVN VERA-KVN
VERA KVN
KaVA
K
10.7
6.1
8.1
0.4
0.3
0.2
Q
22.4
9.1
14.3
0.8
0.5
0.3
Sensitivities (1σ) are listed in unit of mJy.
Integration time of 120 seconds and 4 hours are assumed for baseline and image
sensitivities, respectively. Total bandwidth of 256 MHz (for continuum emission)is assumed for all the calculations. In the case of narrower bandwidth of 15.625 KHz(for maser emission), sensitivities can be calculated by multiplying a factor of 128.

Note that the receiver temperature of the VERA antenna includes the temperature
increase due to the feedome loss and the spill-over effect. In Mizusawa, typical systemtemperature in the K band is Tsys = 150 K in fine weather of winter season, butsometimes rises above Tsys = 300 K in summer season. The system temperature
at Iriki station shows a similar tendency to that in Mizusawa. In Ogasawara andIshigakijima, typical system temperature is similar to that for summer in Mizusawa
site, with typical optical depth of τ0 = 0.2 ∼ 0.3. The typical system temperaturein the Q band in Mizusawa is Tsys = 250 K in fine weather of winter season, andTsys = 300 − 400 K in summer season. The typical system temperature in Ogasawara
and Ishigakijima in the Q band is larger than that in Mizusawa also.
The typical system temperature in the K band at all KVN stations is around 100 K
in winter season. In summer season, it increases up to ∼300 K. In the Q band, thetypical system temperature is around 150 K in winter season and 250 K in summer
season at Yonsei and Tamna. The system temperature of Ulsan in the Q band is about
40 K lower than the other two KVN stations. This is mainly due to the difference inreceiver noise temperature (see Table 5).

3.6

Calibrator Information

The NRAO VLBA calibrator survey is very useful to search for a continuum source
which can be used as a reference source to carry out the delay, bandpass, and phasecalibrations. The source list of this calibrator survey can be found at the following
VLBA homepage,
http://www.vlba.nrao.edu/astro/calib/index.shtml.
For delay calibrations and bandpass calibrations, calibrators with 1 Jy or brighter are
strongly recommended as listed in the VLBA fringe finder survey:
http://www.aoc.nrao.edu/~analysts/vlba/ffs.html.
19Interval of observing calibrator scans must be shorter than 1 hour to track the delay
and delay rate in the correlation process.
500

500
K-bandQ-band
400

300

300
T [K]

T [K]

400

200

200

100

100

0

May 2004

Sep

Jan 2005

May

0

Sep

May 2004

Sep

Jan 2005

Date

May

Sep

Date

Figure 10: The receiver noise temperature (blue crosses) and the system noise temperature (red open circles) at the zenith in the K band and the Q band at the Mizusawa
station.

400

400

300

300
T [K]

500

T [K]

500

200

200

100

100

0

2

4

6

8

10

0

12

Month

2

4

6

8

10

12

Month

Figure 11: The zenith system noise temperature (red filled circles) at the K band (left)
and the Q band (right) in the Ulsan station.

3.7

Date Archive

The users who proposed the observations will have an exclusive access the data for
18 months after the correlation. After that period, all the observed data in the
KaVA common-use observation will be released as archive data. Thereafter, archived
data will be available to any user upon request. This policy is applied to eachobservation, even if the proposed observation is comprised of multi-epoch
observations in this season.

20

4

Observation and Data Reduction

4.1

Preparation

After the acceptance of proposals, users are requested to prepare the observing schedule
file two weeks before the observation date. The observer is encouraged to consult acontact person in the KaVA AOC members and/or the assigned support scientist to
prepare the schedule file under the support of the contact person and/or the assigned
support scientist. The schedule submission should be done by a stand-alone vex file.
The examples of KaVA vex file are available at the KaVA CfP web site:
http://veraserver.mtk.nao.ac.jp/restricted/KaVA2014B.html.
On your schedule, we strongly recommend to include at least two fringe finder scans,each lasting 5 or more minutes at the first and latter part of observation in order tosearch the delay and rate offsets for the correlation.

4.2

Observation and Correlation

KaVA members take full responsibility for observation and correlation process, andthus basically proposers will not be asked to take part in observations or correlations.
Observations are proceeded by operators from each side (KVN and VERA) and correlated data is delivered to the users in approximately two months including the time
for media shipping to KJCC at Daejeon.
After the correlation, the user will be notified where the data can be downloaded byemail. The raw data on the recording media (disk or tape) will be recycled within twomonths after the correlation. Therefore, the user should contact the KaVA member
within that period if the user needs re-correlation or correlation under different settings(e.g., with different tracking position).

4.3

Data Reduction

For the KaVA data reduction, the users are encouraged to reduce the data using the
NRAO AIPS software package. The observation data and calibration data will be
provided to the users in a format which AIPS can read.
As for the amplitude calibration, the KaVA’s correlation data in FITS format havethe system temperature measured by the R-sky method and the information of thedependence of aperture efficiency on antenna elevation (gain-curve table). If the user
wants weather information, the information of the temperature, pressure, and humidity
during the observation can be provided.
At present, KaVA does not support for astrometric observations. In case of questions
or problems, the users are encouraged to ask the contact person in KaVA members
and/or the assigned support scientist for supports.

4.4

Further Information

The users can contact any staff member of the KaVA by E-mail (see Table 11).

21

Table 11: Contact persons.
Name
VERA
H. Kobayashi
K. M. Shibata

E-mail address

Related Field

hideyuki.kobayashi@nao.ac.jp
k.m.shibata@nao.ac.jp

T. JikeT. Hirota
M. Honma
KVN
D. Y. Byun
S. S. Lee
T. Jung
D. G. Roh
KaVA
T. Jung
T. Hirota

jike@miz.nao.ac.jp
tomoya.hirota@nao.ac.jp
mareki.honma@nao.ac.jp

Project Director, Total systems
Operation, Schedule management,
Antenna site in general
Geodetic measurement
Performance for each antenna
Phase calibration, Data analysis

bdy@kasi.re.kr
sslee@kasi.re.kr
thjung@kasi.re.kr
dgroh@kasi.re.kr

Array Operation and System Specification
VLBI Performance
Observation Preparation and Data Analysis
Correlation

thjung@kasi.re.kr
tomoya.hirota@nao.ac.jp

User Support Team (UST)
User Support Team (UST)

References[1] KaVA CfP web site: http://veraserver.mtk.nao.ac.jp/restricted/KaVA2014B.html[2] VERA web site: http://veraserver.mtk.nao.ac.jp/index.html[3] KVN web site: http://kvn-web.kasi.re.kr/eng[4] Han et al. 2013, PASP, 125, 539[5] Han et al. 2008, Int. J. Infrared Millimeter Waves, 29, 69[6] Lee et al. 2011, PASP, 128, 1398
[7] Oh et al. 2011, PASJ, 63, 1229

22