The National Astronomical Observatory of Japan (NAO), has an Optical Linked VLBI Experiment Project named OLIVE that directly connects a correlation site wit h some other VLBI observation stations in network by optical fiber, and correlates in real time. 2 Gbps (1 Gsps 2-bit or 2 Gsps 1-bit) or 8 Gbps (4 Gsps 2-bit) VLBI correlator is necessary in OLIVE. We are developing Gigabits correlators (XF type) using special-purpose correlation chips developed by NAO. We have already completed the Ultra Wideband Correlator named UWBC (2 Gsps 2-bit 256 lags) of 15 baselines for the Nobeyama Millimater Array (NMA). The Nobeyama Radio Observatory (NRO) offered the common use of a new wide-band observation system to astronomers since March 1997. We consider that the 2-Gbps VLBI correlator, which is needed in the OLIVE project, is possible to manufacture. It is also possible to manufacture a 8 Gbps-VLBI correlator using the UWBC chip.

We are doing astrometric pulsar VLBI observation with Kashima-Kalyazin 7000 km baseline. K4 correlator is under the development for this observation program. When XF type correlator is used for pulsar processing with gating, attention should be paid to avoid fluctuation on delay result due to fractional bit effect. This influence is serious around the point that bit shift for delay tracking and pulsar period is synchronized. In this paper, the K4 correlation system is introduced and fractional bit effect on pulsar processing is explained.

Weak objects such as stars can only be mapped with VLBI using phase-referencing techniques. Phase-reference mapping is highly sensitive to imperfect interferometer delay models, and therefore cannot generally be performed on data from MKIII correlators for source separations of more than a few minutes of arc. An AIPS task has been developed to replace the correlator model in a UV data set with the VLBA correlator model (CALC 8.0). It is mainly intended for MKIII data which was read into AIPS via the task MK3IN, but can also be used to improve the precision of phase-reference mapping of VLBA data by correcting wrong apriori geometric information. A second task can replace the atmospheric model used in the correlator with measured values and an improved mapping function.

We have written a suite of programs designed to deal with problems peculiar to short-wavelength VLBI. The most important difference between mm-VLBI and cm-VLBI is that one usually wishes to integrate the data for times which are long compared to the atmospheric coherence time. This causes difficulties with standard VLBI data reduction techniques, and mandates the use of the algorithms implemented in our package for accurate results.

A number of nonlinear image deconvolution procedures based on extremizing generalized Shannon entropy, Kullback-Leibler cross-entropy and Renyi information measures are suggested for VLBI mapping with minimal nonlinear distortions. A new approach to phaseless mapping urgent in the case of unreliable closure phases is proposed.

The problem of VLBI image reconstruction is a classical example of an ill-posed problem. A new procedure of gridding with regularization has been developed. This procedure was used in traditional methods (CLEAN, Hybrid) to improve the quality of compact radio source images. A few sources (GRO J1655–40, RY Scuti and Cyg X-1), observed with the VLA and VLBA, were processed with this procedure.

The Mitaka correlator is an FX-type correlator with 10-station inputs, which is designed for space VLBI and will be used for VSOP mainly. We report here the capabilities of the correlator, the results of model comparisons and the preliminary results of fringe test between the satellite HALCA and Japanese ground telescopes.

We describe a space VLBI experiment involving an earth-orbiting satellite (SURFSAT) and simulated satellites, a space VLBI ground tracking station, an array of ground radio telescopes, and a space VLBI correlator. The purpose of this experiment was to provide as complete as possible an end-to-end simulation of space VLBI in preparation for the first space VLBI mission, VSOP, and in particular to test the most critical aspect of space VLBI, viz. the ability to generate a stable and accurate frequency standard (clock) for the orbiting VLBI element.

On February 12, 1997 the world’s first dedicated VLBI spacecraft, HALCA, was successfully launched as the space borne element of the VSOP mission. This paper describes the calibration observations that have been undertaken so far with this spacecraft.

Knowledge of the position angle of an antenna feed is very important for polarization observations. The issue had been developed for ground based antennas but has not been considered for a orbiting antennas. We provide a calculation of the position angle of the Japanese satellite VSOP/HALCA which was successfully launched in a space VLBI mission.

We outline the HALCA Space VLBI mission scheduling process, with special emphasis placed on software that decides when to observe the proposed sources and how to ensure that the highest quality science is obtained. This information will be useful to the many principal investigators whose very high resolution VLBI observations are being supported by the mission.