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    {\small\rm\zihao{6}\songti\thepage\hfill
    \quad\quad ACTA ASTRONOMICA SINICA \hfill
    \hspace{2mm} Vol.44\vspace{2mm}}}} %%%%%%%
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    {\small\rm \zihao{6}\songti suppl.\hfill  X. Y. Hong et al.: VLBI Facilities and Observations in China   %%（作者：题目名称）
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\zihao{5}\songti

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    \begin{document}


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    %第44卷~第1期  %%%第44卷~第1期
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    %Vol.44~ No.1
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    Vol.44~ Supplement
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    \small ACTA ASTRONOMICA SINICA
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      Feb.,~2003 \\[-1.5 true mm] %%January
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\vs\vs\vs \bc {\Large\bf\zihao{2}\heiti
VLBI Facilities and
Observations
in China    %%（文题）
%\\[1ex]
%$\!\!^*$
} %\footnotetext {2001-03-08收到原稿，2001-05-14收到修改稿   %%（文章收到似的日期）

%$\ast$地震科学工程中国地震运动观测网981602、国家攀登项目二级课题全国地震
%运动监测网和GPS测轨&网研究970231003资助项目}   %%（本文资助项目）

\vs\vs{\normalsize\zihao{4}\fangsong X.Y. Hong\up{1},\hs\hs J.
Zhang\up{2}
\hs\&\hs X. Z. Zhang\up{1}}  %%（本文作者）

\vs
({\footnotesize 1~\sho) \\%%（本文作者单位）
 (\footnotesize 2~ {\it Urumqi Astronomical Observatory, NAO, CAS, Urumqi}~ 830011})
 \vs\vs \ec

\normalsize
\begin{quotation}

 \no{\bf A{\scriptsize\bf BSTRACT }}~~\small
There are two radio telescopes working for VLBI observations in
China. One is near Shanghai and the other is near Urumqi. Both are
the members of the European VLBI Network (EVN), International VLBI
Service for Geodesy and Astrometry (IVS), and Asia Pacific
Telescope (APT). The new developments of the two VLBI stations and
the joint international VLBI observations are described, and a new
VLBI correlator in Shanghai is also introduced.
\end{quotation}

\para{\large\bf{1}~~ VLBI STATIONS}

\vs\vn{\bf{1.1~~Sheshan VLBI Station}}

 The Sheshan (also called Seshan) 25-meter radio telescope is an
alt-az antenna run by Shanghai Astronomical Observatory (SHAO),
Chinese Academy of Sciences (CAS). The telescope is located about
30\,km west of Shanghai.

The radio telescope started its operation in 1987. It is one of
the five main astronomical facilities of Chinese National
Astronomical Observatories. The VLBI station is a member of the
EVN, IVS, and APT.

%\medskip
{\bf Antenna} The station is located at the longitude of 121\dg 11'
59'' E and the latitude of 31\dg 05' 57'' N,
with a height (ground) of 5 meters above sea level. Some
parameters of the antenna are listed below.

  Diameter :  25 meters

  Antenna type: Kashegelun Beam wave-guide

  Seat-rack type:  Azimuth-pitching ring

 Main surface precision: 0.65 mm (rms)

  Point precision: 20'' (rms)

  Rolling range:  Azimuth : -86\dg to 425\dg;
   Elevation: 5\dg to 88\dg

  Maximum rolling speed:   Azimuth :  0.55\dg/sec;
Elevation: 0.28\dg/sec

%\medskip
\vs{\bf Receivers}
 Five bands for VLBI observations are available at Sheshan VLBI
station: L band (18\,cm), C band (6\,cm), K band (1.3\,cm), and S/X
band (13/3.6\,cm). The parameters of the receivers are listed in
Table 1. Column 1 gives the observation band. The frequency range
is listed in column 2, followed by the efficiency of each band in
column 3. The receiver type, polarization model, and system
temperature are listed in columns 4, 5 and 6, respectively.

The L, C, and K bands are used for astrophysics and S/X double
frequencies are used for geodesy. X band is also used for
astrophysical observations sometimes.

The X-band receiver system has been upgraded to the wide-band
system in Dec. 2000. Sheshan station participates in the wide-band
experiments of geodynamics for IVS observation since 2001.

\newpage
\bc{\small\bf

 Table 1~~   Receivers of sheshan station
}\\[2mm]

\fns \tabcolsep 4mm
\begin{tabular}{cccccc}
\hline\\[-3.6mm]\hline
 Band    & Bandwidth    &    Eff.       &      Type        & Polarization &   $T_{system}$ \\
(cm)    & (MHz)        & ({$\%$})      &                  &           & (K)        \\
(1)     &  (2)         &    (3)        &     (4)          & (5)       &  (6)       \\
\hline
18  (L) &$ 1620-1680 $ &    40         & Room Temperature & LCP \&RCP & {$\sim$ 100}\\
13  (S) &$ 2150-2350 $ &    45         & Room Temperature & RCP       & {$\sim$ 100}\\
 6  (C) &$ 4700-5100 $ &    58         & Cryogenic        & LCP       & {$45-50$}   \\
3.6 (X) &$8200-9000  $ &    48         & Cryogenic        & RCP       & {$\sim$ 50} \\
1.3 (K )&$22100-22600$ & {$\sim$20}    & Cryogenic        & RCP \&LCP & {$\sim$110} \\
 \hline\\[-3.6mm]\hline
\end{tabular}
\ec

{\bf Recording system}
 There are three recording systems (VLBA, MKIV and S2) at Sheshan
VLBI station. Both thick and thin tapes are available for VLBA and
MKIV recording system.

MKIV upgrade of Sheshan station was completed successfully in
2000. Sheshan station participated in the two-head recording test
with 512\,Mbit/s by EVN organization in Oct 2001. Fringes to Sheshan
station of both head-stacks have been found successfully. The
performance of the observing system of Shanghai station has been
more advanced over the last few years.

Sheshan station is also equipped with Canadian S2 VLBI recording
system. The system is being used for APT, VSOP, and other ad hoc
VLBI observations.

{\bf Future plans}
 Upgrade of frequency switching system at Sheshan station is going
on. The work will be finished at the end of 2002. The frequency
switch could be done in three minutes between two of C, K, and S/X
bands. This will be very good for the multi-frequency
observations.

A new Hydrogen Maser has been booked from Datum for Sheshan VLBI
station. We will get the new hydrogen clock at the end of 2003.

New dual-polarization receivers for C and L bands are being made
with cooperation of ASTRON (the Netherlands).

%\begin{figure}
%\plotone{25mb.psd} \caption{  }
%\end{figure}

\vn{\bf{1.2~~Nanshan VLBI station}}

 Nanshan 25\,m radio telescope is run by Urumqi Astronomical
Observatory (UAO), NAOC, CAS. It is located  at south 70\,km from
Urumqi city.

The radio telescope has been in operation since 1993. It is
another one of the five main astronomical facilities of Chinese
National Astronomical Observatories. Like Sheshan VLBI station,
Nanshan VLBI station is also a member of the EVN, IVS, and APT.


{\bf Antenna} The antenna is located at the longitude of 87\dg 11' E
and the latitude of 43\dg 20' N, with a height above sea
level of 2080 meters (ground). Some parameters of the antenna are
listed below.

 Diameter:  25 meters

 Antenna type: Kashegelun Beam wave-guide

 Seat-rack type:  Azimuth-pitching ring

 Point precision: 15''(rms)

 Rolling range:  Azimuth : -270\dg to 270\dg;
   Elevation: 4\dg to 89\dg

 Maximum rolling speed:   Azimuth :  1.0\dg/sec;
Elevation: 0.5\dg/sec


{\bf Receivers} It has been outfitted with receivers for six wavelength bands
centered near 92, 18, 13/3.6, 6 and 1.3\,cm. Table 2 summarizes the
relevant information. Columns are the same as those in Table 1.

A new receiver with double polarizations and Cryogenic system for
L band has been made. It was installed in July, 2002. The new
system is being tested.

\newpage
\bc{\small\bf

 Table 2~~   VLBI Receivers of Nanshan Station
}\\[2mm]

\fns \tabcolsep 4mm
\begin{tabular}{cccccc}
\hline\\[-3.6mm]\hline
 Band     &   Bandwidth   & Eff. & Type        & Polarization& $T_{system}$\\
 (cm)    &    (MHz)      & (\%) &             &             &  (K)\\
 (1)     &     (2)       &  (3) &     (4)     &  (5)        &  (6) \\
 \hline
92  (P)  & $ 314-340   $ &  30  &   Room Temp &   LCP       &  150 \\
18  (L)  & $1400-1720  $ &  52  &   Cryogenic &  L/RCP      &   25 \\
13  (S)  & $2150-2450  $ &  48  &   Room Temp &   RCP       &  100 \\
6   (C)  & $ 4750-5150 $ &  55  &   Cryogenic &   LCP       &   38 \\
3.6 (X)  & $8200-8600  $ &  50  &   Cryogenic &   RCP       &   45 \\
1.3 (K)  & $22200-24500$ &  35  &   Cryogenic &   LCP       &  180 \\
 \hline\\[-3.6mm]\hline
\end{tabular}
\ec

\vs{\bf Recording System} There are four recording systems (MKII, MKIIIA, MKIV and K4) at
Nanshan VLBI station. Both thick and thin tapes are available for
MKIII and MKIV recording systems.

Nanshan station was first equipped with MKII recording system. The
system is still available and is used for some ad hoc VLBI
observations with Russian telescopes.

The MKIII recording system was upgraded to MKIV in 2000. Some
problem occurred after the upgrade because of  the un-normal MKIII
system. The problem was solved in 2001. Nanshan station
participated in the two-head recording test with 512Mbit/s by EVN
organization in Oct 2001. Fringes to Urumqi station of both
head-stacks have been found successfully.

Nanshan Station is also equipped with Japanese K4 VLBI recording
system.

\vs{\bf Future plans} A new dual-polarization receiver for C band is being made with
cooperation of MPIfR (Germany).

Nanshan station is planning to have a new Hydrogen Maser with
stability of 10$^{-15}$ or even higher.

\para{\large\bf{2}~~SHANGHAI VLBI COORRELATOR}

\vn The Shanghai VLBI correlator is located in VLBI Laboratory of
National Astronomical Observatories. The correlator is supported
by Chinese VLBI Network (CVN), and also named CVN correlator. The
project of CVN correlator started in 1995. The first fringes of
astronomical observation data were obtained from the CVN
correlator in 2000. During the development of the correlator, the
NRAO experts give very successful helps for us. The CVN correlator
is a two-station FX mode correlator. It uses two Penny \& Giles
reproducers for tape reproduction.

\vn{\bf{2.1~~The main specification of the CVN correlator}}

{\bf Stations}: 2 stations, 1 baseline.

{\bf Inputs}: Each station support one Penny \& Giles
tape reproducer and one VLBA PBD with 8 IF channels.

{\bf Formats}: VLBA formatted data, and Mark III Mode B
unrestricted, Mark III Modes A \& C, with some restrictions, and a
subset of Mark IV.

{\bf Timing}:
Sampling rate 32, 16, 8, 4, 2 Msamp/sec.

{\bf FFT}: 2 FFT engines, FFT sizes 64, 128, 256, 512,
1024 and 2048 points/channel, 2048 point FFT in 16 $\mu s$.

{\bf Quantization}: Supports 2 bit 4 level, and 1 bit 2
level.

{\bf Archive}: The results of CVN correlator should be
written to disk files in FITS data format. The files can be
transferred via FTP.

\newpage
\vspace*{1mm}\no{\bf{2.2~~ The results}}

  After obtaining the first fringes, the CVN
correlator processed more than 20 observations of astrophysics,
geodetic, test purpose and spectral observations.

Figure 1 and 2 show the first fringes and results comparing
between CVN and JIVE correrator.

\begin{figure}[tbph]
\center {\includegraphics [bb=0 0 340 214,scale=1]{fig1.eps}}

   \parbox[tb]{12cm}
   %{\hspace{3.5cm}
  { %\center
   \footnotesize

   Fig.\,1~~ First fringes on Shanghai correlator made
available on Aug 8, 2000. It is the un-calibrated spectrum of DA193
for a single IF at X band on Sheshan-Urumqi baseline.}

    \end{figure}



\vn{\bf{2.3~~Future plans}}

 A new playback system, based on hard disk array, is developing now
for CVN Correlator. The Penny and Giles tape playback system will
be replaced by a new system which is fully compatible with tape
playback system, including data format, tracks, control commands
and the status of playback system. CVN Correlator will use new
playback system before the end of 2002.

Pre-design of 4-station correlator started. It should be beginning
to develop in next year if the fund problem is solved. The
4-station correlator should use disk array and new FFT chips to
reduce the size and power.

To use the present two stations correlator as test equipment, we
plan to make real time VLBI experiments after the new playback
system is established.

\para{\large\bf{3}~~VLBI OBSERVATIONS}

\vn{\bf{3.1~~EVN}}

 The EVN is a collaboration of the major Radio Astronomical
Institutes in Europe \& China, and performs high angular
resolution observations of Cosmic radio sources. It is a large
scale astronomical facility that is open to astronomers all over
Europe and the rest of the world.

Sheshan and Nanshan VLBI stations have been the members of EVN
since 1994. The resolution of EVN increases by three times in
direction of the east-west by jointing Sheshan and Nanshan VLBI
stations. The two stations play an important role for the high
angular resolution observations.

There are three or four sessions for EVN observations each year
with about 20 experiments of each session.  A lot of scientific
results have been obtained. The publications of EVN can be found
on the web of EVN (www.evlbi.org).

Hong et al. (2001) obtained a sub-sample of VLBI image of
EGRET-detected AGNs. They observed 15 EGRET detected sources,
which have not enough VLBI observations, with EVN at 5\,GHz. The
high angular resolution images of the sample have been gotten with
joint observations of Sheshan and Nanshan stations. The images of
1229-021 and 1604+159 were shown in Figure 3 which showed core-jet
structures.

\begin{figure}[tbph]
\center {\includegraphics [bb=0 0 340 425,scale=1]{fig2.eps}}

   \parbox[tb]{12cm}
   %{\hspace{3.5cm}
  { %\center
   \footnotesize

   Fig.\,2~~ Comparisons of correlator output. {\it (top):}
Shanghai correlator; {\it (bottom):} JIVE correlator. It is the
un-calibrated spectrum of DA193 for 4 IFs at X band on
Medicina-Robledo baseline. The same data spanning 1 minute from
N01X2 experiment was used.}

    \end{figure}
    \begin{figure}[h]
\center {\includegraphics [bb=0 0 340 454,scale=0.9]{fig3.eps}}

   \parbox[tb]{14cm}
   %{\hspace{3.5cm}
  { %\center
   \footnotesize

   Fig.\,3~~ (top): The VLBI image of 1229-021 at 5\,GHz,
Peak flux=0.30\,Jy/beam, contour levels = $9.1\times 10^{4}
\times$ (-1, 1, 2, 4, 8, 16, 32, 64, 128, 256) Jy/beam; ({\it
right}) The VLBI image of 1604+159 at 5\,GHz, Peak
flux=0.18\,Jy/beam, contour levels = $2.5\times 10^{4}\times$ (-1,
1, 2, 4, 8, 16, 32, 64, 128, 256)\,Jy/beam}

    \end{figure}

\vspace*{1mm}\no{\bf{3.2~~IVS}}

 IVS is an international collaboration of organizations which
operate or support Very Long Baseline Interferometry (VLBI)
components. IVS provides a service which supports geodetic and
astrometric work on reference systems, Earth science research, and
operational activities.

IVS provides data and products for the scientific community. Some
of the products are a terrestrial reference frame (TRF), the
international celestial reference frame (ICRF), and Earth
orientation parameters (EOP). All IVS data and products are
archived.

IVS products contribute to research in many areas, such as the
solid Earth, tides, studies of the vertical, and VLBI technique
improvement.

Sheshan and Nanshan VLBI stations joined IVS when it was
established in early 1999. Sheshan and Urumqi stations participate
about 16 to 20 experiments each year (each experiment continuing
24 hours observations).

Before IVS was established, Sheshan and Nanshan joined the
geodetic VLBI observations, e.g. CORE program which is organized
by NASA.

\vn{\bf{3.3~~APSG}}

 The main object of the Asia-Pacific Space Geodynamics (APSG)
Program is to unite all relevant activities in the region into a
cooperative research project in plate tectonic, crustal motion and
deformation, and sea level change in the area. This will provide a
synergistic umbrella for scientists in the region to cooperate and
to contribute to the better understanding of the processes
involved and better prediction of major disastrous events. A major
impetus for this program has been the emergence of space geodetic
techniques with mm measurement capability.

All countries in Asia-Pacific area are urged to join in this
project, while countries outside the area are warmly invited to
participate. The project will promote international academic
exchange and scientific cooperation, and will contribute to the
scientific research level of the developing countries in this
area.

Sheshan and Nanshan VLBI stations are the main stations of APSG
for the VLBI technique and have participated in all APSG
experiments.

\vn{\bf{3.4~~VSOP}}

 The Very Long Baseline Interferometry Space Observatory Programme
(VSOP), which was launched in February 1997, stands for the VLBI
Space Observatory Programme, a radio astronomy space mission led
by the Institute of Space and Astronautical Science and the
National Astronomical Observatory of Japan.

Shanghai Astronomical Observatory has been an important partner in
VSOP observations, FOR both the peer-reviewed General Observing
Time observations and the mission-led Survey Program.

The VSOP Survey Program is one of the major science endeavors of
the mission. This program is systematically imaging the 264
brightest and most compact AGNs at 5\,GHz, to form an unprecedented
data base of the most energetic objects in the Universe. This will
aid astronomers to understand the phenomena occurring in these
AGNs, are most likely related to the super-massive black holes
believed to exist at the centers of these objects, and will be
very useful in planning future space VLBI missions such as VSOP-2.

The degree of international collaboration required for VSOP
observations is illustrated by the fact that the first paper from
the Survey Program (Hirabayashi et al. 1998, 2000) has 77 authors
from 25 institutions in 12 countries. It is very pleasant to be
able to record Shanghai Astronomical Observatory's role as one of
the most active ground radio telescopes in the program.

The importance of the Sheshan VLBI station is underlined by the
fact it provides a considerable improvement in the east---west
extent of the European VLBI Network, and a similar improvement in
the north--south extent of the southern hemisphere based S2
network. The fact that the Sheshan VLBI station  has both an S2
and a VLBA recorder makes participation in almost all VSOP
observations possible, without the time-consuming tape copying
required for some other telescopes. According to our records,
Shanghai Astronomical Observatory has participated in over 160
VSOP observations to date, which is a very significant, and highly
valued contribution.

\vn{\bf{3.5~~Ad-hoc VLBI observations}}

{\bf Radar VLBI} The radar VLBI method represents potentially a powerful tool for
investigating space objects without emitting. The combination of
both techniques - radar for good range and radial velocity
resolution and VLBI for angle and angular rate information -
results in three dimensional measurements. Possible applications
cover the fields of research on near earth asteroids,
investigation of short periodic variation of Earth group planets
rotation and investigation of space debris (Tucarri et al. 2002).

Sheshan and Nanshan VLBI stations with other VLBI stations (Bear
Lakes RT-64, Svetloe RT-32, Noto RT-32, Torun RT-32) have done
some Radar VLBI experiments for the study of the Solar System
allowed to discover the population of asteroids crossing the Earth
orbit (NEA) and realize the problem named Asteroid Impact Hazard
by using Evpatoria RT-70 to emitter radar signal.


{\bf LFVN} Nanshan VLBI station joined Low Frequency VLBI Network (LFVN)
project at wavelength of 92\,cm. This activity allows to keep in
operation the large radio telescopes of former Soviet Union
countries, to accumulate the necessary VLBI experience for new
generation of antennas staff and create the necessary
prerequisites for its integrating with EVN.


%\begin{figure}
%\plotone{evng.ps} \caption{L }
%\end{figure}

\vs\vn{\bf ACKNOWLEDGEMENTS}~~ This research was supported by the National
Natural Science Foundation of China, Foundation of Chinese Academy
of Sciences (19973103).

\vs\bc
{\bf References}
\ec

\vspace{-4mm}
\no \fns

 \nref Hirabayashi H. et al., 1998, Sciences, 281, 1825
\nref Hirabayashi H. et al., 2000, PASJ, 52, 955 \nref Hong X,
Jiang, D.R., Schilizzi, R.T. et al., 2001, In: Schilizzi  R. T.,
Vogel, S. N., Paresce, F., and Elvis, M. S. (eds.) Galaxies and
Their Constituents at The Highest Angular Resolutions. IAU
Symposium 205. 116 \nref Tuccari  G., Molotov  I., Buttaccio  S.,
et al., Proceedings of the 6th European VLBI Network Symposium, 13

\end{CJK}
\end{document}
