The launch of SELENE, which acquired the first direct tracking data over the farside of the Moon by the use of 4-way Doppler data between a relay satellite and the main satellite, has resulted in a dramatic improvement of the knowledge of the global lunar gravity field[1,2]. In addition to the 4-way Doppler data, same-beam differential VLBI data between the two sub-satellites and two stations o...

One of the unique characteristics of the Key Stone Project VLBI system is its design for automation. The observation system is highly automated and frequent geodetic VLBI experiments can be performed without the need for human operations. The observation system is designed so that anybody can operate the system with a minimal amount of training. This paper gives an overview of the system and it...

We present results on the compact steep-spectrum quasar 3C 48 from observations with the Very Long Baseline Array (VLBA), the Multi-Element Radio Linked Interferometer Network (MERLIN) and the European Very long baseline interferometry (VLBI) Network (EVN) at multiple radio frequencies. In the 1.5-GHz VLBI images, the radio jet is characterized by a series of bright knots. The active nucleus is...

Simultaneous very long baseline interferometry (VLBI) and water vapor radiometer (WVR) measurements on a 21-km baseline showed that calibration by WVRs removed a significant fraction of the effect of tropospheric delay fluctuations for these experiments. From comparison of the residual delay variations within scans and between scans, the total tropospheric contribution to the delay residuals fo...

One of the methods, used to link the free Hipparcos reference system to the conventional extragalactic reference system, is the indirect method using the rapidly rotating terrestrial reference system as an intermediary. We solve the Earth orientation parameters, referred to the preliminary Hipparcos reference frame H37C, from the observations made by the classical methods of optical astrometry ...

The VSOP terminal is a new data-acquisition system for the Very-Long-Baseline Interferometry (VLBI). This terminal was primarily designed for ground telescopes in the VLBI Space Observatory Programme (VSOP). New technologies; higher-order sampling and digital filtering techniques, were introduced in the development. A cassette cart was also introduced, which supports 24-hour unattended operatio...

The vicinity of the supermassive black hole associated with the compact radio source Sagittarius (Sgr) A* is believed to dominate the observed emission at wavelengths near and shorter than ∼ 1 millimeter. We show that a general relativistic accretion flow, heated via the plasma wave heating mechanism, is consistent with the polarization and recent mm-VLBI observations of Sgr A* for an inclinati...

Understanding and monitoring the solar corona and solar wind is important for many applications like telecommunications or geomagnetic studies. Coronal electron density models have been derived by various techniques over the last 45 years, principally by analysing the effect of the corona on spacecraft tracking. Here we show that recent observational data from very long baseline interferometry ...

VLBI observations of blazars provide the closest look at compact jets that are thought to be responsible for the variable emission of blazars from radio to γ-ray wavelengths. It appears that flux variability at different wavelengths is connected to changes in jet structure near its base. The changes happen on timescales of weeks or less, which require frequent VLBI monitoring to follow. Current...