Overview of the Twelfth 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 twelfth meeting of the Technical Development Center was held on March 10, 1998 at the Kashima Space Research Center of 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 the Communications Research Laboratory (CRL), opened the meeting.

2. Activity Reports by the Special Members

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

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

Seiichi Shimada reported on the effect of horizontal atmospheric asymmetry in GPS data analysis. He mentioned that the estimated horizontal station position had been improved but this is is not the case for the vertical position. He also demonstrated water vapor distribution in a time-space domain obtained from GPS data analysis.

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 of the Maritime Safety Agency as follows.
System improvement in accuracy targeting to 1 cm which is going on at the Shimosato SLR station has entered a final phase.
Measurements using a mobile SLR station made at Chichijima Island on the Philippine sea plate and which were separated by several years show motion of the island at 6 cm/year, which is consistent with VLBI measurements. Last summer the mobile station was located at Ishigakijima island. The measurements could barely be carried out due to the system's age. Next fiscal year, the mobile SLR station will be located at Wakkanai on Hokkaido.
The Hydrographic Department is planning to establish a fully automated GPS observation station at Danjo islands located west of Kyushyu which uses a solar battery and satellite communications link.
Deployment of the D-GPS network by the Aids to Navigation Department is going on as scheduled. About 30 sites will be established by the end of FY 1998.

Nobeyama Radio Observatory, National Astronomical Observatory (Noriyuki Kawaguchi)

Noriyuki Kawaguchi reported on the current status of the VERA project and VSOP as follows. The main aim of the VERA (VLBI Exploration of Radio Astrometry) project has been slightly modified to emphasize the observation of invisible objects, that is, the precise measurement of the attractive motion of maser sources due to the gravitational field around black holes. An angle resolution (of better than) in an order of 10 micro arcsecs is required for this purpose. To obtain this angle resolution at least four, and if possible more than six, VLBI stations will be necessary for the VERA network in Japan. Urmuqi station will be a key station in improving the imaging ability of the VERA network. Furthermore, VERA can have better continuum sensitivity than VLBA at millimeter-wavelength by having wider observing bandwidth.
He also demonstrated the idea of a synthesis antenna by connecting a number of antennas distributed throughout Japan using ATM optical links in a "writing with one stroke" manner. He demonstrated that this idea would allow observations at up to 8 Gbps, if the communication link has 10-Gbps speed and five stations are connected.
As for the VSOP, Kawaguchi reported that "HALCA" is in good condition and space VLBI observations are carried out almost everyday. He told us that he hopes to compare VSOP results with high-angle resolution observation made by VERA at a higher frequency in the future.
Finally, he requested the Technical Development Center (TDC) at CRL to maintain the 34-m antenna as long as possible because of its importance to the Japanese VLBI community and to continue the development of a reliable gigabit recorder. He also hoped CRL would promote the development of a VLBI network in Japan connected by optical fiber links like a KSP.

Tokyo Gakugei University (Kachishige Sato)

Kachishige Sato introduced his recent work on the model calculation of rheological slip without friction at the subducting plate boundary. This study was motivated by the measurement of postseismic crustal deformation measured by GPS after the 1994 Sanriku-Haruka-Oki earthquake, he said. He evaluated two types of rheological model for lower crust and uppermost mantle, the "Maxwell model" and the "three-element solid model", by comparing the actual observation results. He concluded that the "three-element solid model" better explains the observations.

Kobori Research Complex, Kajima Corporation (Masayuki Takemura)

Masayuki Takemura reported on his recent work investigating the historical seismograph records of the 1923 Kanto earthquake. He pointed out that what happens after large earthquakes is important in predicting future earthquakes. He said, we can learn many things from historically large earthquakes.

Geographical Survey Institute (Mikio Tobita)

Mikio Tobita reported that the Field System, which is VLBI system control software developed by the US VLBI group, has been successfully installed at the 26-m antenna site at Kashima. A fringe test using the Field System was successfully carried out on March 3, 1998, and good fringes were detected.
He also reported that the construction of a 32-m antenna at Tsukuba is complete. A fringe test was done on March 20. This new antenna has a high-speed slewing rate of up to 3 deg/sec. The reference point of the antenna was designed not to vary over 5 mm per year. This will be monitored through a local survey.

Mizusawa Astrogeodynamics Observatory, National Astronomical Observatory (Hideo Hanada)

Hideo Hanada briefly reported on the current status of RISE (Research In SElenology) in the SELENE (SELenological and ENgineering Explorer) project. According to his report, SELENE will enter the PM phase in FY 1998. A workshop relating to RISE was held at Mizusawa in January, 1998.

3. Technical Development Reports

3.1 VLBI Technology Developed at CRL

VLBI technology developed at CRL was reviewd by CRL members.

3.1.1 Automated Observations System (Yasuhiro Koyama)

CRL has been developing automated observation/operation software for Japanese VLBI since the early 1980's. These are "KAOS", "MAOS", "NKAOS", and "KANAMEISHI" in chronological order. The latest one is for the Keystone Project. The format of schedule files tends to be unified into the VEX format in the case of international VLBI. Therefore our VLBI operation software should be modified to accept the VEX format. On the other hand, the Field System, which was developed by the US VLBI group, makes it possible to control hardware developed by CRL, such as K4 and GBR recorders. Details are reported in this issue (see page 6).

3.1.2 Antenna and Front-end System (Noriyuki Kurihara)

CRL developed not only a receiver system for the 26-m antenna at Kashima but also a GSI VLBI system. CRL has been cooperating with the National Institute of Polar Research on the Antarctic VLBI project. We can say that CRL has contributed to the progress of domestic VLBI stations. Thus CRL has the potential of designing an antenna system up to 30-m and a high-quality and reliable S/X receiver system. CRL can also evaluate the total performance of VLBI antenna.

3.1.3 Back-end and Recorder (Hitoshi Kiuchi)

We developed a K-3 back-end and a recorder system, which are compatible with the Mark-III system. Then we developed a K-4 back-end and recorder which are more compact than the K-3 system's and easy to operate. After the K-4 VLBI system, a KSP recorder equipped with an automatic tape changer was developed. This changer enables us to make observations for a long time without an operator. It also makes observation very easy.

3.1.4 Real-time VLBI Technique (Hitoshi Kiuchi)

A real-time VLBI technique has been developed by CRL in collaboration with the Nippon Telegraph and Telephone Corporation (NTT). High-speed optical fiber links were constructed between four KSP stations by NTT. We also developed a real-time correlation processing technique using data transmitted through high-speed links. Now we are conducting routine VLBI observations using 256-Mbps data.

3.1.5 Bandwidth Synthesizing Technique (Tetsuro Kondo)

The history of bandwidth synthesizing software in Japan was briefly reviewed. Initially it took more than one hour to process only a single observation of about six minutes. Now this has become less than one minute due to improvements in software and computer hardware. One of the special members of TDC requested the development of real-time bandwidth synthesizing software.

3.1.6 Data Analysis (Yukio Takahashi)

Data analysis software dedicated to the geodetic VLBI developed by CRL was reviewd. The software has been being updated year by year to reflect the latest physical model and theory into analysis. The current software (for KSP) is third generation in Japan. We plan to implement the following function in the future, such as astronomical and geodetic applications, wide-band VLBI analysis, differential-VLBI analysis, and phase synthesis analysis. One of the special members hoped TDC/CRL would contribute to the data analysis of the VERA project.

3.2 Current Status of the Keystone Project (Crustal Deformation Observation System in the Tokyo Metropolitan Area)

3.2.1 VLBI System (Kouichi Sebata)

Kouichi Sebata reported on the current status of KSP-VLBI as follows. Measurement accuracy has been drastically improved since last autumn due to the change in observation tactics from a daily five-hour session to a 24-hour session every other day. Even though KSP is designed for ease of use in operation, sometimes recovery is difficult from R\&D experiments or unusual accidents. We are compiling an operation manual as well as operation know-how in our computer to allow special knowledge to be utilized and shared with operator. As the KSP operator can access these manuals through the WWW, he/she can cope with most difficulties without any specialist aid.

3.2.2 SLR System (Hiroo Kunimori)

Hiroo Kunimori reported on the current status of the KSP SLR system as follows. The second observation campaign of Kashima and Koganei stations was successfully carried out. Observations were made at all four stations. KSP SLR started regular observations on February 16, 1998.

3.3 R&D Experiment Reports

3.3.1 Survey Observation of Radio Sources using KSP (Akihiro Kaneko)

Akihiro Kaneko reported on survey observation using the KSP VLBI facility. Last autumn, KSP changed routine operation from an everyday basis to an every other day basis. Survey observations were then carried out during the rest period of routine KSP operation. The purpose of survey observation is to obtain information about the angle size of radio sources available for VLBI. So far 120 candidates in the Parks catalogue have been surveyed, and fringes were successfully detected on 57 sources.

3.4 Others

3.4.1 Current Status of Kashima 34-m Antenna (Eiji Kawai)

The current status of the Kashima 34-m antenna was reported on by Eiji Kawai. As almost ten years has passed since the antenna was constructed, deterioration can be seen in every part. As the antenna is old, continuous upkeep is required to maintain it in good condition. One of the special members of TDC appreciated CRL's efforts in assisting and collaborating on VSOP. He requested CRL to keep the 34-m antenna as long as possible. After Kawai's talk a general question was raised concerning the lifetime of the antenna. Replying to the question, Mikio Tobita of GSI commented that it was 30 years in the case of a new GSI 32-m antenna.

3.4.2 Current Status of Next Generation VLBI (Junichi Nakajima)

Junichi Nakajima reported on the current status of the 43 GHz receiver currently under development. He also reported on the interference problem at 1.6 GHz expected to arise from the low altitude communication satellites to be launched in the very near future. The effects and problems are now being investigated. One of the special members commented that this might cause severe interference for the VLBI station in space.

3.4.3 Current Status of NAOCO at Kashima (Tomonari Suzuyama)

NAOCO, a simple correlator developed by the National Astronomical Observatory, is temporarily being installed at Kashima to allow spectrum observations to be made using the 34-m antenna. Tomonari Suzuyama reported that the installation is going well.

4. Closing Greeting

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

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