## Overview of the Tenth TDC Meeting

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

The tenth meeting of the Technical Development Center was held on March 14, 1997 at the Kashima Space Research Center of Communications Research Laboratory.

### Attendance

CRL members
Kuniaki Uchida, Taizoh Yoshino, Shin'ichi Hama, Hitoshi Kiuchi, Akihiro Kaneko, Hiroo Kunimori, Chihiro Miki, Jun Amagai, Kohichi Sebata, Hideyuki Nojiri, Toshimichi Otsubo, Yuko Hanado, Fujinobu Takahashi (KSRC: Kashima Space Research Center), Yukio Takahashi (KSRC), Ryuichi Ichikawa (KSRC), Yasuhiro Koyama (KSRC), Mamoru Sekido (KSRC), Junichi Nakajima (KSRC), Eiji Kawai (KSRC), Tetsuro Kondo (KSRC)
Special members
Nobuyuki Kawano (National Astronomical Observatory), Kazuo Shibuya (National Institute of Polar Research), Mikio Tobita (Geographical Survey Institute), Masayuki Fujita (Hydrographic Department, Maritime Safety Agency),
Following special members could not attend:
Noriyuki Kawaguchi (National Astronomical Observatory), Kosuke Heki (National Astronomical Observatory), Kazuo Shibuya (National Institute of Polar Research), Hisashi Hirabayashi (Institute of Space and Astronautical Science), Yoshimitsu Okada( National Research Institute for Science and Disaster Prevention), Teruyuki Kato (Earthquake Research Institute, University of Tokyo)

### 1. Opening Greeting

Kuniaki Uchida, the director of IERS TDC at Communications Research Lab., opened the meeting.

### 2. Activity Reports of Each Organization by the Special Members

The special members reported on the current status of the activities of their organizations.

### Geographical Survey Institute (Mikio Tobita)

Mikio Tobita reported geodetic project at Asia-Pacific area in which GSI is involved.
The second meeting of the Permanent Committee on GIS infrastructure for Asia and the Pacific area was held in Sydney, Australia in October, 1996.
At this meeting it was proposed that geodetic observation should be carried out in October, 1997 using fixed space geodetic stations available. The purpose of these observations is to establish precise geodetic reference points in Asia Pacific area. In particular co-location of different techniques and local tie observations must be carried out. It is expected that 6 VLBI stations, 16-20 SLR stations, 20 DORIS stations, 6 PRARE stations and more than 50 GPS stations will participate in this project. As for VLBI observations, they are expected to be the Fairbanks, Hobart, GSI-Kashima, Kokee, Shanghai and Urumqi stations. Observation schedule will be prepared by Shanghai using a SKED program. Correlation processing will be carried out by GSFC. Baseline analysis and distribution of data will be carried out by Shangahi.

### National Astronomical Observatory (Nobuyuki Kawano)

Nobuyuki Kawano reported current status and future plan of the National Astronomical Observatory (NAO).
The second stage of future plan will start from the 10th anniversary of NAO (next year). Re-organization on a fairly large scale is also planned. A review of NAO by outsiders has already begun. The VLBI and VSOP projects has already completed the first stage review process by domestic reviewers.
A VSOP satellite was successfully launched on February 12, 1997. A main dish antenna was also successfully deployed.
Budgetary request for VERA (VLBI Exploration of Radio Astrometry) for the fiscal year 1998 will be proposed to the Ministry of Finance. The number of antennas has been reduced from two antennas at each site to one. Investigation of dark matter is added to the purposes of the project.
In collaboration with ISAS and NASDA, a RISE satellite will be launched in 2003 using a HII-A rocket.
NIPR (National Institute of Polar Research) is promoting an Antarctic VLBI project. Equipments necessary for VLBI will be shipped to Syowa Station, Antarctica this year (Nov. 1997) by the 39th Japanese Antarctic Research Expedition (JARE-39). \begin{c2head}

### Hydrographic Department, Maritime Safety Agency (Masayuki Fujita)

Masayuki Fujita reported on geodetic observations by the Hydrographic Department, Maritime Safety Agency.
The first round of measurements of first-order control points using a mobile SLR system were completed last fiscal year (FY1995). The second round of measurements started, and a Chichijima Island point was measured from September to December, 1996. Ishigakijima Island position will be measured from July to November, 1997.
A fixed SLR system at Shimosato has been operated since 1982. Current accuracy of the system is about 3-4 cm. Fujita said that he wants to improve it to 1 cm. Initially the photo-detection system will be upgraded.
Continuous GPS measurements (24 hours a day) are carried out in the Kanto area.
A D-GPS (1.5-2 m accuracy) system developed by the Aids to Navigation Department is preparing its routine service. About 30 reference sites will be established by 1999. The Hydrographic Department plans to make geodetic observations using reference D-GPS sites.

### 3. Report on TWAA96 (Yukio Takahashi)

Yukio Takahashi reported on TWAA96 (Technical Workshop for APT and APSG 1996) held in Kashima on December 10-13, 1996. See page 6 for details.

### 4.1. Current Status of Key Stone Project (Crustal Deformation Observation System in the Tokyo Metropolitan Area) (Yasuhiro Koyama)

Yasuhiro Koyama reported on the current status of KSP VLBI as follows.
Daily observations on the full network (4 stations : Kashima, Koganei, Miura, and Tateyama) have been carried out since September, 1996. Recently the success rate for baseline analysis of the daily observations has become nearly a hundred percent. So far the results of baseline analyses can be announced at the latest within one and a half day after daily observation (00:00-05:00 JST) is finished. Kashima station had a problem with an air conditioner in a receiver room, and this makes a baseline analysis result much worse. However, accuracy of result was improved drastically by stopping operation of air conditioner temporarily. Present accuracy (formal error) is 2 mm in baseline length for a 2 MHz video frequency width observation.
As for unmanned operation at remote stations it is important how fast we can recover a system from any trouble. Koyama said, We could make it in 3 days for the most inconvenient station, Tateyama.''

Q: Why is accuracy improved by stopping air conditioner operation?
A: An air conditioner in a receiver room in an antenna at Kashima has a problem. When it works, room temperature changes periodically with a period of about 20 minutes with temperature amplitude of about 3 degree Celsius. This results in a fast apparent clock change difficult to remove. When the air conditioner is stopped, room temperature change becomes more gradual. Consequently the apparent clock change becomes estimatable. This may improve an accuracy in the analysis.

### 4.2. Current Status of KSP SLR System (Hiroo Kunimori)

Hiroo Kunimori reported on the current status of SLR system in the KSP as follows.
Kashima and Koganei SLR stations made an engineering level test observation on January 29 - February 14, 1997. The purpose of this test observation is to evaluate the total operational flow from an observation to an analysis and to determine any problems. Return signals were detected for more than 40 passes both at Kashima and Koganei. Single-shot rms value of the uncertainty in measured distance was 10-25 mm for LAGEOS and its variation within a pass was large. The normal point rms value was 3-8 mm. Stability of ground target was +/- 5 mm for 7 days. None of these values meets the specification for the system. To satisfy the specifications both hardware and software will be upgraded and an engineering level test will be continued.

### 4.3. Multimedia Virtual Laboratory --- Its Application to VLBI (Shin'ichi Hama)

Shin'ichi Hama reported on the Multimedia Virtual Laboratory (MVL) project, in particular emphasised in applications for VLBI use. The concept of the MVL was proposed by the Telecommunications Technology Council, in consideration of recent technological developments in telecommunications. At present there is no unified idea about MVL. Concerning VLBI applications, joint ownership of huge amount of data is attractive to provide good prospect for a distributed analysis system and for a virtual big antenna (see page 13 for details).

Q: Image of MVL is obscure. Is it to use a remote laboratory and to perform some experiment in an office without going to the site?
A: Each person has his own idea. Some merely considers the MVL as an extension of the current TV conference system. As for VLBI, it is considered as a way to transfer a huge amount of data with fast speed.
C: At GSI we are thinking about possibilities of applying MVL for circulation of remote sensing data. It will be of great help for distribution of information to the public.

### 5.1 Overview of Development of Next Generation VLBI Terminals and Their Compatibility (Yukio Takahashi)

Yukio Takahashi reviewed all types of VLBI terminals currently used in the world. He also summarized their compatibility and their accuracy in baseline analyses. Details are reported in this issue (see page 15).

### 5.2 Current Status of Development of Gigabit Recorder at CRL (Junichi Nakajima)

Junichi Nkajima reported on the current development status of Gigabit Recorder (GBR-1000) introduced in the last TDC news (VLBI TDC News CRL, No.9, pp.17-18, 1996). In addition to the report, he proposed the establishment of domestic next generation VLBI development team'' aiming to develop a millimeter wave length wide band VLBI technique on the basis of a bottom-up approach (not top-down one). He also stressed that CRL should return to its starting point (or spirit) when K3 VLBI system was developed. Namely CRL should be a user as well as a developer of VLBI technology. A plan and a developed technology should be announced world-wide. As for the development of recorder, we should recognize that an open-reel-type recorder is quite different from an cassette-tape-type one equipped with a helical scanning head. Hence we only think about minimum compatibility between them when a new recorder is developed.

Q: How about supply of tape? Is it easy to get at reasonable prices?
A: Yes. GBR-1000 itself is used at commercial TV stations. There is no problem concerning supply and price of tape.
C: Even though it is difficult to do radio astronomy as a main objective at CRL because it can not be an official goal right now, please proceed with the development of a millimeter wave length technology.

### 5.3. Development of High Density Recorder as an Expansion of K-4 Recorder (Hitoshi Kiuchi)

Hitoshi Kiuch reported on plans for high density recorder development. In his presentation he emphasized the following points. What TDC should do is to contribute system development to realize a high accuracy measurement. However development in the CRL is not a satisfactory condition at the present time. Development of VLBI system so far never exceeds but merely follows those in USA. To overcome this situation we should develop a high density recorder with a data rate of 2048 Mbps (64 Mbps x 32 ch or 128 Mbps x 16 ch) dedicated to geodetic VLBI. There are good prospects for realizing a video converter with a video bandwidth wider than 64 MHz. As for the recorder, there are thought to be no technical barriers for development.

Q: What is the difference between GBR-1000 and this system?
A: Target is different. GBR-1000 is dedicated to a radio astronomy, while this system is mainly for precise geodetic applications.
C: Existence of two types of recorder is not happy for users.

### 5.4 Perspective Image of Next Generation VLBI Terminal (Tetsuro Kondo)

Tetsuro Kondo presented his expectations concerning the development of the next-generation VLBI terminal. In his presentation he summarized ideal feedback loop structures in the relation between technical development and scientific progress into following two categories. One is an improve accuracy'' pursuit loop. In this feedback loop, observation system is designed to achieve the best measurement accuracy from a technical point of view. Cost-effectiveness is sometimes regarded as an unimportant factor in system development. Measurement with high accuracy will be a seed for scientific study. Conversely, scientific results will stimulate more accurate system development. The other one is a spread promotion'' loop. Being different from the previous one, this type of loop aims to reduce cost instead of increasing accuracy to distribute the system widely in the world. Miniaturization of system can also be a goal. Even though accuracy of measurements is sacrificed, widely distributed terminals in case of VLBI will give a new perspective view in a scientific study. CRL should proceed with both types of development if possible.

### 6. Closing Greeting

The closing greeting was delivered by Fujinobu Takahashi, the vice-director of IERS TDC at Communications Research Laboratory.