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Volume 54 (2008)
- Issue 4 Pages 203-
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- Issue 2 Pages 59-
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Volume 54, Issue 4
Displaying 1-7 of 7 articles from this issue
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[in Japanese], [in Japanese], [in Japanese]2008 Volume 54 Issue 4 Pages 203
Published: 2008
Released on J-STAGE: February 25, 2013
JOURNAL FREE ACCESSDownload PDF (135K) -
Kazuhiro Takashima, Misao Ishihara2008 Volume 54 Issue 4 Pages 205-219
Published: 2008
Released on J-STAGE: February 25, 2013
JOURNAL FREE ACCESSGeographical Survey Institute (GSI) carries out the Very Long Baseline Survey using the technology of Very Long Baseline Interferometory (VLBI) since 1984 in order to detect plate movements and crustal deformation around Japanese islands, and to connect with international terrestrial reference frame, and to monitor the global changes such as sea level rise or earth orientation. GSI introduced transportable VLBI antennas through collaboration with Radio Research Laboratory (RRL), and then carried out VLBI experiments at nine sites in Japan and Korea for 12 years from 1984 to 1995. In 1995, Shintotsukawa VLBI station was established as the first step to fixed domestic VLBI antenna network. In Japan, as of April 2002, the old Tokyo Datum was legally superseded by a brand new one, the Japanese Geodetic Datum 2000 (JGD2000) based on International Terrestrial Reference Frame (ITRF). Kashima VLBI station which participated in long term international VLBI observations and domestic mobile VLBI stations contributed to define the framework of JGD2000. International VLBI Service for Geodesy and Astrometry (IVS) was established in 1999 as an organization promoting global collaboration on VLBI activity. GSI participates in IVS as an observing station and a correlation center. This paper reports the transition of VLBI at GSI from introduction period to present.View full abstractDownload PDF (12712K) -
Kensuke Kokado, Shinobu Kurihara, Shigeru Matsuzaka2008 Volume 54 Issue 4 Pages 221-231
Published: 2008
Released on J-STAGE: February 25, 2013
JOURNAL FREE ACCESSTsukuba 32 m VLBI station of Geographical Survey Institute (GSI) was constructed in 1998, and it has been operational for more than ten years. Tsukuba 32m VLBI station is a target of the azimuth from origin for horizontal coordinates in Japan and a core station of the domestic VLBI observation by GSI. In the past 10 years, we have improved the observation system for advancement of VLBI observation, such as update of the recording system and introduction of the data transfer system via high-speed network. The number of the sessions at Tsukuba station reached 190 sessions per year in 2008, and the station is important for International VLBI Service for Geodesy and Astrometry (IVS). GSI also has Tsukuba VLBI correlation center, and has processed the data of domestic and international VLBI sessions. The correlation system was shifted from hardware correlation system to software system in 2005, and the software system has often updated since then. Now, Tsukuba VLBI correlation center processes the data of more than 100 sessions in a year.View full abstractDownload PDF (13439K) -
Tetsuro Kondo, Yasuhiro Koyama, Ryuichi Ichikawa, Mamoru Sekido, Eiji ...2008 Volume 54 Issue 4 Pages 233-248
Published: 2008
Released on J-STAGE: February 25, 2013
JOURNAL FREE ACCESSThe National Institute of Information and Communications Technology (NICT) has been contributing to the development of a Very Long Baseline Interferometry (VLBI) system as a technology development center (TDC) of the International VLBI Service for Geodesy and Astrometry (IVS). Since the 1990s NICT has been developing a series of VLBI samplers and hard disk recording systems called K5. The K5 system is designed in such a manner that a commercially sold PC can be used for data recording, and it is dedicated to the transfer of observed raw data through the Internet (e-VLBI). A software correlator has been developed to process the K5 VLBI data. A series of samplers named the Versatile Scientific Sampling Processor (VSSP) can be directly connected to a host PC throuh a PCI-bus intrrface or a USH 2.0 interface, and the latest sampler named VSSP32 supports 4 ch×1 bit×64 MHz sampling per PC (thus, four PCs can support conventional 16 ch observations with a total data rate of 1024 Mbps). Currently, VSSP series samplers are widely being employed not only for geodetic VLBI observations but also for radio astronomical observations and precise time comparisons.View full abstractDownload PDF (11863K) -
Yasuhiro Koyama, Tetsuro Kondo, Mamoru Sekido, Junichi Nakajima, Morit ...2008 Volume 54 Issue 4 Pages 249-258
Published: 2008
Released on J-STAGE: February 25, 2013
JOURNAL FREE ACCESSThe development of the K5 VLBI (very lo ng baseline interferometry) system began in 1999. One of the purposes for developing the K5 VLBI system was to realize real-time VLBI observation and correlation processing to be performed under different settings and modes according to the characteristics of the observing sessions. To realize this purpose, diverse component systems were developed to allow the flexible combination of these components. The specifications of the VLBI Standard Interface (VSI), on the other hand, were discussed and designed within the international VLBI community to allow easy interconnectivity between multiple components for VLBI observations and correlation processing developed independently by different institutions. Through the hardware specifications of VSI (VSI-H), both electrical and physical properties of the interface have been defined and standardized. By applying the defined specifications, differently designed VLBI systems can be expected to easily connect and work together. In this paper, we report our efforts to adapt VSI-H specifications into the design of the K5 VLBI system.View full abstractDownload PDF (12075K) -
Atsutoshi Ishii, Ryuichi Ichikawa, Hiroshi Takiguchi, Hiromitsu Kuboki ...2008 Volume 54 Issue 4 Pages 259-268
Published: 2008
Released on J-STAGE: February 25, 2013
JOURNAL FREE ACCESSThe laser-pumped Cs gas-cell type atomic frequency standard (hereafter, we called the “Cs gas cell oscillator”), this was developed in recent years, has a stability between a hydrogen maser oscillator and a Cs beam-type frequency standard. The square root of Allan variance for this atomic frequency standard is 2×10-13 at 10 sec and reaches 2.5×10-14 at about 1000 sec. This stability is good enough to maintain coherence for VLBI observations at the frequencies of 2 and 8 GHz. It is very small and easy to operate compared with the hydrogen maser oscillator. The size and weight of this oscillator is roughly equal to a desktop PC. If we can use this Cs gas-cell oscillator as a frequency standard for VLBI, the space required for a VLBI station will be dramatically reduced. Hence, this oscillator is suitable for a transportable VLBI station. A geodetic VLBI experiment with a 110 km baseline was conducted, where the Cs gas-cell oscillator was used at one station, and a hydrogen maser oscillator was used at the other station. The length of the baseline vector estimated by this experiment was coincident within 1 mm compared with the result of an experiment using only conventional hydrogen maser oscillators. The results of these experiments indicated that the Cs gas-cell oscillator is sufficiently stable to use as a frequency standard for geodetic VLBI observations.View full abstractDownload PDF (4790K) -
Hiroshi Takaba, Hiroshi Sudou, Ken'ichi Wakamatsu, Noriyuki Kawaguchi, ...2008 Volume 54 Issue 4 Pages 269-278
Published: 2008
Released on J-STAGE: February 25, 2013
JOURNAL FREE ACCESSThis paper reports the development of a gigabit real-time e-VLBI (Very Long Baseline Interferometry) geodetic system. For an experiment using the Super-Sinet of the National Institute of Informatics, the 32-m telescope at the Geographical Survey Institute in Tsukuba City, the National Astronomical Observatory of Japan in Mitaka City, and the 11-m telescope at Gifu University were connected using a 2.4 Gbps optical line. By two-way transmission through the optical line, S/X band data was transmitted by uplink and downlink at 2 Gbps. Their distributed correlation processing by the correlators at the National Astronomical Observatory of Japan and Gifu University realized the world's fastest real-time geodesy e-VLBI at 4 Gbps. Gaussian fitting was employed for the delay search from broadband data, enabling very accurate searches. A delay search method using phase inclination was also developed and proved to be about as accurate as the Gaussian fitting method. For the Japanese Dynamic Earth (JADE) observation by VLBI at the Geographical Survey Institute, observations by a conventional magnetic recording system (K4/K5) and the e-VLBI system were conducted simultaneously and their delays were compared. Unlike the delay of K4/K5, that of the e-VLBI was found to migrate by several hundred picoseconds a day. This is cancelled by K4/K5, which injects P-cal signals in front of the feed horn for bandwidth synthesis. However, e-VLBI may show the temperature fluctuations along the cable length between the observation room and the receiver. By baseline analysis, we could obtain geodetic results according to which this fluctuation was absorbed by clock estimation and the difference of the baseline length between K4/K5 and e-VLBI less than 3 mm.View full abstractDownload PDF (4321K)
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