Overview of the Eleventh TDC Meeting

Tetsuro Kondo (kondo(AT)nict.go.jp)
Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-0012, Japan

The eleventh TDC meeting hela at the headquaters of Communications Research Laboratory on September 18, 1997.

The eleventh meeting of the Technical Development Center was held on September 18, 1997 at the Communications Research Laboratory.


CRL members Special members Following special members could not attend:


1. Opening Greeting

Fujinobu Takahashi, the vice-director of IERS TDC at Communications Research Laboratory (CRL), opened the meeting with an introductory statement of the technical development center at CRL.

2. Reorganization of CRL and the Key Stone Project (Taizoh Yoshino)

Taizoh Yoshino represented a brief history of the IERS emphasizing its relation to the technical development center at CRL. After the reorganization of the VLBI participants in the IERS, the CRL was nominated again as one of the Technical Development Centers in September 1996. In the CRL, a team system was newly introduced in July 1997, where each team devotes to a specific subject in a limited period. The Keystone Project Team was born to run one of the major projects in the CRL. In the Keystone Project Team, crustal deformation in the Tokyo metropolitan area is studied using VLBI and SLR technology. Technical improvement is also expected as one of the activities. Relationship between the existing research sections and the team to perform technical developments was also explained.

3. Activity Reports of Each Organization by the Special Members

Each special member reported on the current status of the activities of each organization.

Nobeyama Radio Observatory, National Astronomical Observatory (Noriyuki Kawaguchi)

Noriyuki Kawaguchi reported on the current status of Nobeyama Radio Observatory and space VLBI project (VSOP) as follows. The VSOP is successfully going on, this is greatly owing to an international collaboration. He also mentioned a format converter developed by himself, which makes it possible to correlate the data taken by different recording systems. So far it is possible to convert among three kinds of recording formats. At the end of his report he expressed his hope that the technical development center at CRL will be a center able to produce an international standard.

Mizusawa Astrogeodynamics Observatory, National Astronomical Observatory (Hideo Hanada)

Hideo Hanada reported that RISE (Research In SElenology) in the SELENE (SELenological and ENgineering Explorer) project, which will be launched in 2003 to the Moon, and a lander will make a soft landing on the Moon while an orbiter stays in lunar orbit, has entered the development phase this fiscal year. However for budgetary reasons, the SELENE project is obliged to change its initial form to decrease costs. As a result of re-planning the lunar lander comes to play the role of an engine for the orbiter, even though both had independent engines in the initial plan. Differential VLBI using signals from the lunar lander and a relay satellite which will be released from the orbiter is therefore postponed to one year after launch.

Geographical Survey Institute (Mikio Tobita)

Mikio Tobita reported Project'97 promoted by the Geographical Survey Institute (GSI), the Communications Research Laboratory (CRL), and the Hydrographic Department, Maritime Safety Agency (JHD) as a joint project. The Project'97 aims (1) to tie GPS, VLBI, and SLR, and to connect them to the origin of Japan geographic coordinates for the GIS campaign observations taken in October, 1997, (2) to make collocation observations of GPS, VLBI and SLR for the IERS, and (3) to tie KSP-VLBI/CRL, SLR and GPS/JHD, and a 26m antenna at Kashima/GSI to a GPS network operated by GSI.
He also expressed his thanks to the technical development center for continuous technical support during installation of the correlation processing system at GSI. Now a K-4 type correlator, available to process three baselines, is in operation at the GSI.
As for the experiment, proposed by Tobita at the 9th TDC meeting held in September 1996, with KSP antennas being utilized as fiducial points in SAR images by pointing them to an expected satellite direction, he reported that it did not get good results, i.e., no antenna was identified in the SAR images. Antennas were merely pointed to the satellite direction without any special treatment, such as placing a metal plane in front of the antenna feed horn to increase reflecting signals. This result was therefore partly expected before the experiment. Tobita however asked a continuous cooperation of CRL group to improve this experiment to obtain reasonable results because it is an excellent idea.

Hydrographic Department, Maritime Safety Agency (Masayuki Fujita)

Masayuki Fujita reported on the current status of SLR and GPS observations carried out by the Hydrographic Department, Maritime Safety Agency as follows.
SLR measurements made at Chichijima Island on the Philippine sea plate separated by several years shows motion of the island consistent with that obtained by others, such as VLBI measurements. Presently the position of Ishigakijima Island is being measured. The Hydrographic Department plans to start GPS observations on an uninhabited island next fiscal year.
Deployment of D-GPS network consisting of more than 20 sites in Japan promoted by the Aids to Navigation Department will be completed in the next fiscal year, which is earlier than the original schedule by one year.

National Research Institute for Science and Disaster Prevention (Seiichi Shimada)

After a brief self-introduction Seiichi Shimada talked about the current tendency of GPS analysis software to emphasize treatment of atmospheric delay effects in the analysis. They consider the effect of horizontal gradients in the zenith excess delays, as well as taking the mapping function into consideration. As for water vapor effects, a trial using numerical weather prediction data is starting to produce good initial conditions in the analysis.

Tokyo Gakugei University (Kachishige Sato)

Kachisige Sato, who moved from Mizusawa Astrogeodynamics Observatory, National Astronomical Observatory, introduced his recent studies. He has been investigating plate motion and deformation using space geodetic data. Comparing the results from VLBI and GPS data, he suggested that VLBI data are consistent with a plate motion model based on geological evidence, while GPS data seem to show some inconsistency with the model. The same inconsistency can be seen in SLR data, he said. He plans to investigate this discrepancy more detail.

Kobori Research Complex, Kajima Corporation (Masayuki Takemura)

Masayuki Takemura, a specialist of strong ground motions of earthquakes, said that he wants to contribute to the TDC/CRL from a unique position, because his major field is slightly different from that of other special members. Then he introduced his recent work investigating the 1995 Hyogo-ken Nanbu earthquake in comparison with historical large earthquakes. This comparative study shows that the Hyogo-ken Nanbu earthquake is not a special one but a common one often occurring in Japan as an intra-plate earthquake, he said. He pointed out that the local ground condition is an important factor for damage caused by earthquakes. It can be learned from the ground motion estimated from the directions of overturning tombstones. In the case of large earthquakes like the 1923 Kanto earthquake, damage becomes much larger and wider in area. We should recognize that we cannot adopt all results learned from the Hyogo-ken Nanbu earthquake to much larger earthquakes.

4. Technical Development Reports

4.1. Preliminary Report of 120 hour Continuous Observation on the Key Stone Project (Crustal Deformation Observation System in the Tokyo Metropolitan Area) VLBI Network (Tetsuro Kondo)

CRL has been carrying out daily observations using the real-time KSP VLBI network to monitor crustal deformation around the Tokyo metropolitan area. Tetsuro Kondo reported on an experiment carried out on the KSP VLBI network over 120 hours continuously from July 28 to August 1, 1997. Each session lasted for 24 hours and consisted of about 600 scans. Five sessions are included in the experiment. The main purpose of this experiment is to evaluate the accuracy limit achieved by the current system. Repeatability of measured daily baseline lengths represents a considerable improvement compared with that for routine daily observations of 6 hour duration. Thus daily 6-hour observations on the KSP network are modified to include 24-hour experiments every other day to increase the accuracy of measurements. One of the special members asked, how can the number of scans be increased to such a large number? Kondo replied that this is made possible by real-time correlation processing, which does not require an extra period in each scan which is necessary for tape synchronization in the case of tape-based VLBI. Thus we can reduce the time for each scan, resulting in an increase in the total number of scans.

4.2. Report on Real-time Correlation Processing Software RKATS (Mamoru Sekido)

Real-time correlation processing software RKATS developed for KSP-VLBI system was introduced by Mamoru Sekido. Because of an automatic fringe search and a dynamic clock offset adjustment, which are RKATS's important functions, continuous unmanned operation is achieved, he emphasized. One of the special members asked him, it is important for clock compensation to adjust a rate rather than an offset, isn't it? Is it actually necessary for a hydrogen maser frequency standard to adjust clock offset frequently? Sekido replied as follows. RKATS has both a rate and an offset adjustment function. For a practical use it is enough to adopt only an offset correction. A 1 pps signal of a station clock was sometimes reset to keep a time difference sufficiently small compared with the UTC.

4.3 Analysis of KSP GPS Observations from a Meteorological Point of View (Ryuichi Ichikawa)

Ryuichi Ichikawa reported on results obtained through the comparison between VLBI and GPS measurements which were simultaneously conducted with an experimental continuous observation from July 28 to August 1, 1997. The results showed that time variations can be seen in a geodetic solution of GPS results that are similar to those seen in VLBI results. He also mentioned that scatter in the east-west components obtained by GPS observation became larger when low elevation angles were included in an analysis, and this may be related to an inhomogeneous distribution of water vapor around a station. Regarding a systematic error seen in the position measured by GPS for Tateyama station, one of the KSP stations, he suspected the radome of the GPS antenna of influencing the results.

4.4 Current Status of KSP SLR System (Hiroo Kunimori)

Hiroo Kunimori reported on the current status of SLR system in the KSP as follows. A calibration for optic-electronic packages was carried out using colocation optics at Kashima configuring all four connected to a single telescope and one of lasers transmitting to the ground targets. Results demonstrated system stability to about 2 mm.

4.5. Tie of the KSP Network to the ITRF (Yasuhiro Koyama)

Yasuhiro Koyama reported on the result of experiment using the KSP VLBI network and the Kashima 34 m antenna as follows. The position of Kashima 34 m antenna is well determined in the international terrestrial reference frame (ITRF) through a number of international VLBI sessions. By connecting the KSP network with the Kashima 34 m antenna, station positions of KSP network in the ITRF were determined within a discrepancy of 1 cm for horizontal components and 3 cm for vertical components. Comparing these results with ITRF coordinates of GPS ground bench marks, it is shown that the positions of KSP stations measured by VLBI and GPS are coincident with each other within 2 cm for horizontal and 5 cm for vertical components. However the discrepancies are not so small and the reasons for this are under investigation.

4.6 PCAL System at Urumqi Station (Noriyuki Kurihara)

Noriyuki Kurihara visited Urumqi VLBI station, China to improve the phase calibration (PCAL) system in July, 1997. He reported on the current status of Urumqi station and a preliminary result of VLBI observation carried out just after he installed an improved PCAL system. The new PCAL system seems to be working well but some problems still remain in the total system, he pointed out.

4.7 Current Status of Multimedia Virtual Laboratory Project (Yukio Takahashi)

Yukio Takahashi reported on applications for VLBI use in the Multimedia Virtual Laboratory (MVL) project. As for the VLBI applications, high speed transmission of a huge amount of data and a technique for real-time data processing on distributed stations become key items in system development. He showed an example of ideas about correlation processing as carried out at multiple stations simultaneously with sharing the data.

4.8 A Next Generation VLBI Terminal (Hitoshi Kiuchi)

Hitoshi Kiuchi presented his ideas about a next generation VLBI terminal. According to his idea, a data recorder will consist of 16 channels and each channel will record data at a rate of either 128 Mbps or 256 Mbps. The video bandwidth will be wider than 32 MHz (up to 64 MHz), which is realizable even with current technology. The input/output interface will be unified to use an optical interface.
By adapting parallel processing logic to a correlator, the speed of processing will reach 1 Gps per channel. An FPGA instead of a custom-made LSI will be used for correlator development because the debugging process becomes easier than that with LSI. The differences of recording and data format among VLBI systems throughout the world will be absorbed at the correlator.

4.9 Current Status of Development of Next Generation VLBI System Based on Gigabit Recorder (Junichi Nakajima)

Junichi Nakajima reported on the current status of development of next generation VLBI system based on a gigabit recorder (GBR-1000) as follows. Performance test of the sampler portion was carried out at the Nobeyama Radio Observatory. Auto-correlation was successfully detected by a GICO (GIgabit COrrelator).

4.10 An Evaluation of GPS Time/Frequency Receiver as a VLBI Frequency Standard (Tetsuro Kondo)

\end{c2head} Tetsuro Kondo presented the results of an evaluation of GPS time/frequency receiver as a VLBI frequency standard. He measured the phase difference of 10 MHz signals from two independent GPS time and frequency reference receivers which are locked to GPS satellites. He then calculated Allan variances and coherence loss using the measured data. He said, as a result it is demonstrated that the GPS Time and Frequency Reference Receiver can be used as a frequency standard for frequencies lower than 1 GHz. He also mentioned that if we expand the fringe search process to include searches at least up to a third order phase change against time, then a GPS Time and Frequency Reference Receiver is adoptable as a frequency standard for VLBI operated at even higher frequencies, up to 8 GHz.

4.11 Millisecond Pulsar Observation Using 34 m Antenna at Kashima (Yuko Hanado)

Yuko Hanado introduced a millisecond pulsar observation system and reported on recent observation results. The results show good repeatability due to an upgrade of the software TEMPO which estimates the pulse phase of pulser. A new long-term-drift appears in the results, however. Comments on this report follow. Use of TEMPO as a black box may limit this study in the future. A pulse phase estimation software should be developed along with system development. As for an improvement of signal to noise ratio, a burst sampling technique is suggested.

4.12 Construction of New Station Disseminating Japanese Standard Time and Frequency at LF Band (Michito Imae)

Michito Imae introduced the new station transmitting standard radio waves at the LF band, under construction in Fukushima Prefecture, Japan. CRL is responsible for keeping Japan Standard Time (JST) and dissemination of standard time and frequency. At present, CRL disseminates the JST and frequency using JJY (HF) and JG2AS (LF). However, interference is increasing at HF band, and JG2AS is not a permanent station. The investigation committee organized in CRL for dissemination of more stable and practical signals permanently recommended to unify both stations as a single LF station. Thus construction of the new LF station started. It will transmit standard signals at 40 kHz with a power in excess of 10 kW. Service will start in April, 1999.

4.13 Study on the Basic Technique of Satellite Positioning System (Michito Imae)

A basic technique of a satellite positioning system investigated at CRL, in particular in the field of frequency standards, for the purpose of future use was briefly introduced by Michito Imae. He showed topics which should be studied at CRL as follows: development of an on-board atomic frequency standard, a time keeping technique for a group of on-board clocks, and a technique for precise real-time orbit determination. He also presented his plan to include an atomic clock on the Engineering Test Satellite-VIII (ETS-VIII) which will be launched in 2002 by the National Space Development Agency of JAPAN (NASDA).

5. Closing Greeting

The closing greeting was delivered by Kenichi Okamato, the director of IERS TDC at Communications Research Laboratory.

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