Transportable VLBI antenna development and Cluster antenna

by Y. Takahashi

1. Transportable 2.4m VLBI system

CRL and GSI has developed a small transportable VLBI system for the sea level monitoring system. The change in the long term is suitable to use the tide gauge data of tidal station. The position of the tidal station may be moving in long term by local crustal deformation. Therefore we should measure the movements of tidal station, and its data should be corrected to the change in tide gauge data. We developed the VLBI system in order to measure the movements of tidal stations. As there are many tidal stations in Japan, the system should be transportable and small for Japan narrow roads. 2.4m antenna and receiving system were developed. We confirmed that it has the performance to be used for the VLBI with Kashima 34m antenna to observe the Moon by single dish. We conducted the test VLBI observation with the strong radio source 3C84 with Kashima 34m antenna, and we detected good fringe as shown in Figure-1. This system will be transported to the tidal station near Tokyo in this year, and we will measure the som e tidal stations in Japan for several years.

2. VLBI using four cluster antennas

We conducted the VLBI experiments by new VLBI technique between two antennas in each site on 29th May and 27th June. The 34m and 26m antennas in Kashima of CRL, and 6m and 45m antenna in Nobeyama of Nobeyama Radio Observatory were used for this experiment (Figure-2). The main purposes are (1)relative VLBI, (2)the investigation of integration time longer than 1000 sec, (3)weak source observation such as Cygnus3 and SS433, (4)the characteristic of atmosphere scintillation for the different angle distance less than 10 degree, (5)deformation of large antenna, (6)application of the relative VLBI for the geodesy. At first, we make an analysis of the integration longer than 1,000sec. The coherence loss of correlated amplitudes are caused by the long variation of atmosphere scintillation and hardware stability. The correlated amplitudes become smaller in according to the integration time when it is longer than 600. Signal to Noise Ratio (SNR) becomes maximum when the integration time is about 1,200 sec as shown Figure-3. We continue to make the detail analysis of the reason. The data will be also analysed from the other aspects.

Figure 1. Fringe detection (Source 3C84).

Figure 2. SNR as integration time normalized at 400sec.

Figure 3. VLBI using four antennas cluster.

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