Establishment of the Trans-Pacific VLBI Network for Monitoring the Earth's Variable Rotation

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1. Objectives of the Research: (1) To achieve high-precision measurement of the Earth's variable rotation. (2) To achieve high-precision time synchronization between Kashima (Japan) and Richmond (Florida, USA). (3) To conduct data analysis and improve data analysis software. (4) To establish the management system to smoothly operate the Trans-Atrantic VLBI network (IRIS-P).2. Cooperative Institutes: Although the research group consists solely of the National Astronomical Observatory staff, this research was carried out in close cooperation with two institutes, namely the Communications Research Laboratory (CRL, Japan) and the National Geodetic Survey (NGS, USA). CRL offered the use of K-3 VLBI system at Kashima, and NGS offered the arrangement of the US stations participation in IRIS-P network, as well as correlation of observed video tapes at the correlation center in the United States Naval Observatory.3. Research Plans: (1) 1987: To initiate the IRSI-P network composed of Kashima of … More CRL (Japan). Richmond (Florida, USA), Ft. Davis (Texas, USA), and Fairbanks (Alaska, USA) and operate it smoothly as the network center for acquiring the data which meet the reseatch objectives, and to conduct data analysis and compare the results with those of CRL and NGS. (2) 1988: To improve observation schedule based on the results derived from 1987 observations, and to refine analysis software.4. Research Activities: (1) Observation: Monthly 24-hour session observations were completely made as scheduled, by sending 3 observers to Kashima every time. (2) Network Operation: Within half a year from the initiation of the network, the system was established to shipping tapes to and from the correlation center and to send observation schedules to the participating stations through an electronic mail. (3) Data Analysis and Software Improvement: With the aid of CRL cooperation, the results obtained by our software were carefully examined and thereby necessary improvement was made. In June 1988, S. Manabe of the research group visited NGS to discuss matters on data analysis. Eventually, the presently used software has sufficient capability for data analysis as the network center of IRIS-P.5. Scientific Findings: (1) We determined the Earth's rotation with the precision better than 1 cm. Thus the IRIS-P network is the best among existing three VLBI networks. (2) We found errors of the positions of extragalactic quasars of the order of a few milli-arcseconds. (3) We tied the positions of the participating stations with the global terretrial reference system with the precision of a few cm. (4) We achieved time synchronization between Kashima and Richmond with the precision of 0.5 ns. Less