To monitor the atmospheric conditions in the radio astronomical observations, we have developed a new type of the radio seeing monitor, which enables us to measure the atmospheric turbulence in real-time and in a wide range of the direction in the celestial hemisphere. The base of the measurement system is a radio interferometer, in which the beacon waves of low earth orbit satellites (LEO satellites) for mobile communication system are received as reference signals. Time variations of the differences in arrival time are measured between element antennas of the interferometer, which are given as phase variations of cross-power spectra of the signals received by the antennas. we have made test observations of the atmospheric disturbances, and obtained a typical profile that the magnitude of the phase variations tends to increase with decreasing elevation angle of the reference source, i.e., the LEO satellite. In addition, we found that the magnitude of the phase variations is locally enhanced in some directions.
A real-time VLBI (Very Long Baseline Interferometer) system using conventional telephone lines is proposed. This system enables us to check if the VLBI network is alive by on-line manner, which is useful to reduce the loss of observation time caused by system malfunctions. In this system, a beacon of satellite or the emission from cosmic maser sources is received. The narrow-band spectral profile of the received signal leads us to compress the data up to the size less than the capacity of transmission rate on conventional telephone lines, that is to say a few tens of kbps. Additional devices for the real-time operation are A-D converters, PCs and modems, which are not special ones. As the link between the VLBI stations is performed by the conventional way, the system is applied not only to domestic VLBI networks, but also to international VLBI networks, in which a part of the VLBI stations is located in rural place. It has been confirmed that the cross-correlation is clearly detected for the compressed beacon wave data.