Noriyuki Kawaguchi (National Astronomical Observatory),
Hideo Hanada (National Astronomical Observatory),
Mikio Tobita (Geographical Survey Institute),
Masayuki Fujita (Hydrographic Department, Maritime Safety Agency)
Seiichi Shimada (National Research Institute for Science and Disaster
Prevention),
Kachishige Sato (Tokyo Gakugei University)
Masayuki Takemura (Kobori Research Complex, Kajima Corporation)
Following special members could not attend:
Tetsuo Sasao (National Astronomical Observatory),
Shuhei Okubo (Earthquake Research Institute, University of Tokyo),
Minutes
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.
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.
