Basic Experiments of Real-Time VLBI Using Public Communication Line

为了实时观测鹿儿岛和水泽直径分别为6米和10米的地球同步卫星的19 GHz信标信号，研制了一个由基带变频器、数据采集单元、信号传输单元和互相关器组成的射电望远镜附属子系统。并开发了数据传输和互相关软件。VLBI利用基线长度约为1300公里的地球静止卫星的信标波与射电望远镜相连的子系统进行观测。我们证实了互相关是实时获得的。对于互相关数据，我们检查了是否可以检测到大气传播延迟的波动。详细分析了互相关数据中相位起伏的来源，得到了以下结果：(1)接收机噪声的贡献可以忽略不计；(2)DRIF…(3)作为主振荡器安装在射电望远镜上的氢脉泽振荡器的频率偏差是引起持续时间小于10秒的快速相位变化的主要来源，而在大于10秒的范围内其影响可以忽略不计。我们得出的结论是，持续时间在10-100秒之间的位相波动是由大气扰动引起的。研究表明：(1)利用商用A/D转换器、个人计算机和通信设备等简单、低成本的设备，可以实现对VLBI系统的实时诊断；(2)通过对地球同步卫星信标波的VLBI观测，可以检测到大气扰动引起的无线电传播时延的波动；(3)可以用小直径天线构建大气扰动的无线电监测系统，低成本接收器和基于商业的数据处理单元。该项目的成果以论文和会议记录的形式发表，如IEICE会刊、SPIE会刊、ISAP会刊等。对该项目的后续研究正在进行中，将发表更多的论文。较少

For real-time VIBL observations of the 19GHz beacon signals from geostationary satellites with the Kagoshima 6-m diameter and the Mizusawa 10-m diameter radio telescopes, a subsystem attached to the radio telescopes is developed, which consist of base-band frequency converters, data acquisition units, signals transmission units and a cross-correlator. The software for data transmission and cross-correlation is also developed. VLBI observations with the subsystem attached to the radio telescopes were made using the beacons waves of the geostationary satellites, where the baseline length was about 1300 km. We confirmed that the cross-correlation was obtained in real time. For the cross-correlation data, we have checked if the fluctuations of atmospheric propagation delay can be detected. Origins of the phase fluctuations included in the cross-correlation data were analyzed in detail, and we obtained following results ; (1) contribution of the receiver noise was negligibly small, (2) drif … More t of phase caused by the diurnal motion of the satellite and the effect of the frequency deviation of the beacon signal could be removed from the observed data, and (3) the frequency deviation of hydrogen maser oscillators installed in the radio telescopes as master oscillators was a main source of fast phase variation with the duration shorter than 10 sec, while its effect was negligible at the range of longer than 10 sec. We conclude the phase fluctuations with the duration from 10 to 100 sec are originated from the atmospheric disturbances. In addition, we conclude that smaller diameter antennas, such as 1-m diameter paraboloidal antennas, can be used for detection of the atmospheric disturbances.This project makes it clear that (1) the real-time diagnosis of the VLBI system is achieved with simple and low-cost devices, such as commercial-based A-D converters, personal computers and communication devices, (2) fluctuation of radio propagation delay caused by atmospheric disturbance is detectable by the VLBI observations of the beacon waves of the geostationary satellites, (3) a radio monitoring system of the atmospheric disturbance can be constructed with small diameter antennas, low-cost receivers and commercial-based data processing units. The results obtained by this project are published as papers and proceedings, such as IEICE Transaction, SPIE Proceedings, ISAP Proceedings and so on. A follow-up study of this project is in progress and further papers will be appeared. Less