The Extension of the Asia VLBI Networks by CRL (the Results in Japan-Urumqi VLBI Experiments)

Y.Takahashi1 (takahashi(AT), T.Iwata3, N.Kurihara1, J. Nakajima1, M. Sekido1, M.Imae2, Y.Hanado2, Y.Koyama1, Dong You Suo and Urumqi VLBI group, and Shanghai VLBI group

1 Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314, Japan

2 Communications Research Laboratory
4-2-1 Nukui-kita, Koganei, Tokyo 184, Japan

3 Now at National Space Development Agency of Japan

(being appeared in the proceedings of APT'95 (Asia Pacific Telescope meeting 1995))

1. Introduction

The Asia and Pacific VLBI network makes the widest VLBI network which cooperation with Australia, China, Japan, Russia and Hawaii. The east and central Asia is very interested to study the crustal dynamics. This area is on the Eurasian Plate. The India Plate collides to the central Asia, and Himaraya Mts. are created on the front of the collision. The central Asia are pressed by the India plate motion, and the East Asia is pushed out toward the east direction, that is, toward the Japan archipelago. This movement is related with the crustal deformation in Japan archipelago. It is recently considered that the deformation of east Asia makes the micro plate (Amur plate) on the Eurasian plate and the other micro plate (Ohotsuku Sea plate) on the North American plate. Figure 1 shows the crustal deformation in Asia area. Four plates, such as North American plate (or Ohotsuku Sea plate), Eurasian plate (or Amur plate), Pacific plate and Phillipin Sea plate, collide together near the Japan archipelago, and the big earthquakes occurred repeatedly. The deformation near Japan archipelago should be studied as the deformation of the whole Asia area.
Figure 1. The deformation in the Asia and near Japan Archipelago.

As concerning that the Asia area is important, we promote the Asia and Pacific VLBI experiment. The joint VLBI experiments with Urumqi conducted in 1994 and 1995. The results in these experiments are described.

Furthermore, we conducted the pulser VLBI observation with Russia in 1995, and we will conduct the VLBI observation in the spring, 1996 again. We also have the plan to set the K4 VLBI terminal to Shanghai in China, Kalyazin in Russia and Wettzel in Germany. Therefore, we can extend the VLBI network in Asia.

2. Joint Experiments with Urumqi

The results of Japan and Urumqi experiments in 1994 and 1995 are described. Table 1 shows the overview of the experiments in 1994, 1995.

Table 1. Residual of Urumqi experiment

In 1994, the phase calibration is not good, and we do not used the phase calibration data. The phase information among the channels was fixed to the phase relationship of one observation near the middle of experiment. The observation used the strong source, and the SNR is very large and the phase fluctuation is stable for each channel. In this method, the other observations has pseudo delay by the incorrect phase information. The phase relationship among channels is changeable during the experiment, and its change was equal with the clock change. We need many changes in clock. The residual was very large.

In 1995, the phase calibration was considered to be well, but the residual was also large. Figure 2 shows the change in the clock of Urumqi in 1995. The change in clock was very large and we needed many changes in clock almost every hours.
Figure 2. Residual of Delay in 1995.

The coherence loss was checked for these experiments. The whole observation is divided into the several segments shorter than 1 minute (a few 10 seconds). The correlated amplitude are calculated for each segment. The coherence correlated amplitude is obtained from an average as the complex values over the all segments to include the phase information. On the other hand, we can obtain the incoherence correlated amplitude from the average of correlated amplitude for each segments, that is, it is averaged without the phase information between the segments. The ratio of two correlated amplitudes means the coherence loss caused by the phase stability, such as atmospheric scintillation, the stability of reference signal and the stability of system. The noise affects on the ratio of two correlated amplitude in the case that a single noise ratio (SNR) is less than 10, and the pseudo coherence loss appears for the small SNR. Therefore, we can estimate the coherence loss only for large SNR. However, SNR for almost all observation in our experiments is large and our estimation of coherence is correct.

In the 1st experiment, the coherence at X band is almost greater than 85 % shown in Figure 3. Abscissa is sources in the experiment and ordinate is the coherence. The coherence at X band is about 60 % in the second experiment shown Figure 4. The coherence at S band is about 80 %. The coherence loss by the atmospheric scintillation is less than 5 % at X band. This large coherence loss in the second experiment may be caused by the stability of phase calibration or reference frequency (5 MHz) for the short period.
Figure 3. Coherence of 1st experiment in 1995 (The solid line means 85%)

Figure 4. Coherence of 2nd experiment in 1995 (The solid line means 85%)

We show the position of Urumqi. Table 2, 3 show the estimated position XYZ components and Horizontal \& vertical movements of Urumqi station in ITRF93 (International Terestial Reference Frame 1993).

Table 2. Position of Urumqi station in ITRF93

Table 3. Horizontal and vertical position of Urumqi station

The estimated vertical component of the second experiment in 1994 may be incorrect. The XYZ positions of Urumqi station estimated by 1995 experiments may be correct in the precision of 2 cm. The position of horizontal component was measured in the precision less than 5 cm. Figure 5, 6 show the horizontal position (easterly and northterly movement) in ITRF93 obtained from the results of the experiments in 1994 and 1995. %

Figure 5. Horizontal position of Urumqi station in ITRF obtained from the experiments in 1994.

Figure 6. Horizontal position of Urumqi station in ITRF obtained from the experiments in 1995.

We corrected the movement of Urumqi station on Eurasian plate in ITRF93, and we obtained the position of Urumqi station at Epoch 1994.3.1 on the Eurasian plate from the results of 1995 experiments. If the Urumqi station moves on the Eurasian plate due to the crustal deformation, this corrected position becomes different with the results of 1994 experiment. These positions of horizontal components agreed the positions obtained by the 1994 experiments in the precision of 1 cm. This result might mean that the Urumqi station on Eurasia plate and the deformation was not large though the error was a few cm. The positions are shown in Table 3. Figure 7 shows the corrected position obtained from 1995 experiments.

Figure 7. Horizontal position of Urumqi station on Eurasian plate at 1995.3.1 obtained from the experiments in 1995.

3. Japan-Russia Pulsar VLBI Experiment

We conducted the pulsar VLBI experiment since the spring 1995. The station in Russia is Kalyazin 64m antenna. The purpose of these experiments are to measure the precise pulsar position and proper motion of pulsar. We deliver K4 terminal to Kalyazin, and we continue experiments for a few years.

4. Conclusion and Future

We conducted the VLBI experiments with Urumqi or Russia. We succeeded the first experiment with Urumqi station. The Urumqi positions can be estimated in the precision of a few cm. The Urumqi station has some problems yet. However, it is proved that Urumqi station can be used as the VLBI station. We hope to extend the Asia and Pacific VLBI network step by step.

We have a plan to deliver K4 system to the station in the area, such as Kaliazin (Russia), Shanghai (China), Wettzel (Germany). NAO (Narional Astronomical Observatory) delivered K4 system to Urumqi (China) and Crimea. NIPR has a plan to establish the anterctica VLBI network around souther hemisphere using K4 system. Therefore, we can conduct the VLBI experiments in Asia and Pacific area using K4 system.

We also have new VLBI network in Tokyo metropolitan area. We observe sources everyday. Figure 8 shows the change in the correlation amplitude on the baseline between Kashima and Koganei since 31th January 1995. If we find the burst change for some sources in our VLBI network, we will propose VLBI observation in this Asia and Pacific VLBI network.

Figure 8. The change in correlated amplitudes in KSP new project since 31th 1995.

Updated on October 28, 1996. Return to CONTENTS