Chihiro Miki

An application of GPS dual frequency codeless receiver for ionospheric delay to single frequenc band VLBI observation

A dual-frequency codeless Global Positioning System (GPS) receiver for measuring ionospheric delay, called GTR-2, has been developed. Results of a feasibility study of using GTR-2 for single-frequency very-long-baseline interferometry (VLBI) experiments are presented. GTR-2 uses a cross-correlation property of the P-code signals transmitted from GPS satellites to measure ionospheric total electron content (TEC) with a measurement uncertainty of about 2*10/sup 16/ electrons/m/sup 2/ along the line of site to the satellite. Ionospheric compensation of the signal from radio stars is studied using the TEC data obtained from GTR-2. >

Development of a GPS time comparison system and the GPS common-view measurements

An L1 band (1575.42 MHz), C/A (coarse/acquisition) code GPS receiver for precise time comparisons has been developed. GPS measurements in common-view have been carried out between the Korea Standards Research Institute (KSRI) and the Communications Research Laboratory (CRL), Japan. The frequency stability of the KSRI master clock has been measured against the master clock of CRL for 50 d. The frequency stability is about 1 part in 10/sup 13/ for the averaging time of 4 d. >

Calibration of the delay time in the GMS/GPS time transfer receivers using portable reference receivers

The Communications Research Laboratory (CRL) of Japan and the National Measurement Laboratory (NML) of Australia have performed international time transfer using the Geostationary Meteorological Satellite (GMS) and the Global Positioning System (GPS) since 1986. The precision of the time transfer using GPS is 10 ns, while that using GMS is 20 ns. However, there has been a bias of 200 ns between the time transfer results of the two time links, which is mainly due to the estimation error of the delay time in the time transfer receivers. To improve this bias error, CRL developed a portable reference receiver (PRX) for the GMS time transfer to calibrate the delay time in the time transfer receivers. In November and December 1987, a calibration experiment was carried out by the PRX method for GMS and GPS between CRL and NML. As the result of the experiment, the bias was reduced from 200 to 75 ns and the accuracy of the time transfer between CRL and NML was significantly improved. >

VLBI, SLR and GPS observations in the Key Stone Project

A space geodetic observation network has been established around Tokyo, Japan under a project name of Key Stone Project by Communications Research Laboratory. Three space geodetic methods, i.e. Very Long Baseline Interferometry, Satellite Laser Ranging, and Global Positioning System, are involved in the project. As of September, 1997, VLBI and GPS observation facilities at all four stations are operational, whereas developments of SLR observation facilities are in course of final alignment procedures. Daily VLBI observations began in January 1995 with a single baseline between Koganei and Kashima, and the full network observations with four stations began in September 1996. Observations and data analysis of VLBI measurements are fully automated and the analysis results are produced shortly after all observations of an experiment session finished. GPS observations at four sites began in July 1997 and the automatic data collection and analysis system are under developments.

Time comparisons between KSRI and CRL via the geostationary meteorological satellite of Japan

A time comparison system using the ranging signal of the geostationary meteorological satellite (GMS) of Japan has been developed, and GMS measurements have been carried out between Korea Standards Research Institute (KSRI), Korea and Communications Research Laboratory (CRL), Japan. The result of the time comparison has shown that the precision of the GMS time comparison system at KSRI is about 10 ns. The GMS time-comparison system can be used for T/F transfer in the Asian and surrounding oceanic area with a precision of several tens of nanoseconds. >