The Communications Research Laboratory (CRL), Tokyo, Japan, and the Telecommunication Network Laboratory Group, Nippon Telegraph and Telephone Corp., Tokyo, Japan, have developed a highly precise, very long baseline interferometry (VLBI) system using a high speed asynchronous transfer mode (ATM) network. The observed data is transmitted through a 2.488-Gbps ATM network [STM-16/OC-48] instead of being recorded onto magnetic tape. The system was specially designed for the Key Stone Project (KSP), a project begun in 1994 to measure crustal deformation in the Tokyo metropolitan area. Cross-correlation processing and data observations are carried out simultaneously by one operator. It takes about one hour to analyze the data after the observations and correlations are completed. In regular geodetic VLBI experiments run every other day for 24 h, a horizontal position uncertainty of about 2 mm and a vertical position uncertainty of about 10 mm were achieved. The system was designed to enable automated operation throughout the entire process. The results obtained are available to the public via the Internet at http:ksp.crl.go.jp. This system is a significant advance in VLBI and should provide more precise information about crustal deformation in the Tokyo metropolitan area.

Time and Frequency (T/F) transfer systems using space links developed at the Radio Research Laboratories (RRL) are described. The domestic T/F transfer system uses the Japanese communication satellite: CS-2/broadcasting satellite BS-2 and the Global Positioning System (GPS) in addition to the ordinary links of ground TV and Loran-C The Asian area transfer system makes use of the Geostationary Meteorological Satellite (GMS) and a Very Long Baseline Interferometer (VLBI) as well as Loran-C Other systems for international T/F transfers depend on the space techniques of the GPS and the, VLBI. Spread-spectrum equipments for T/F transfers have recently been built to realize both precision and accuracy of about 1 ns via the CS link, together with a 1-m mobile antenna station. Receivers have been developed at RRL to be used routinely for the GPS and GMS T/F transfers on a daily basis with a precision of 10 ns or more and an accuracy of less than 100 ns. T/F transfer experiments using a VLBI system developed at RRL have been conducted on a routine basis about once a month with the U.S. Naval Observatory since April of 1985. The present goal of accuracy is 10 ns with 10-min or longer observations.