The Sixth TDC Meeting

The Sixth meeting of the TDC was held on March 3, 1995 at the conference room of the Kashima Space Research Center, CRL.



CRL members Special members Teruyuki Kato (Earthquake Research Institute, University of Tokyo) could not attend the meeting.

Minutes of the Sixth TDC Meeting

3. Activity reports by the special members

Each special member reported current status and activities of each institute.

Current Status of IRIS-P Network (Nobuyuki Kawano)

VLBI measurements on the IRIS-P network will be continued. The K-4 aquisition terminals will be distributed to stations in China, Tasmania, and Hawaii (or Alaska) gradually starting in June, 1995. Correlation processing will use the VSOP correlator.


Q: How often are you planning to conduct experiments?
A: So far, we don't have an answer, because it depends on the agreement made between the countries involved.

Outline of VLBI System Development at National Astronomical Observatory (Noriyuki Kawaguchi)

TCU (Timing Control Unit) has been developed. TCU enables timing control at recording and/or replaying without use of any formatted data. A VSOP type data aquisition system is developed on the basis of the sampler (DFC-2000) developed by CRL. A sampler with 4 GHz sampling rate and 2 bits resolution was developed and has been evaluated. Test observations start. Burst sampling system, consisting of 4 GHz sampler and 32 Gb memories, can take the data for only 4 sec for fuge amount of data such as required to 500 sec when K-4 is employed.


Q: Who determines the orbit of VSOP?
A: JPL and ISAS.

VLBI Observations at Geograpphical Survey Institute (Takashi Saito)

In FY1994, we conducted domestic VLBI observations on baselines Tonami-Kashima and Kanozan-Kashima. Two sets of VLBI systems equiped with 3.8-m dish antennas are newly installed. One is used as a fixed station at Shintotsugawa in Hokkaido. The other is used as a mobile station and is now stationed at Tsukuba. A hundred and ten GPS receivers are distributed in Japan by GSI. Besides this, a hundred GPS receivers are deployed in the South-Kanto area.


Q: Are GPS observations always carried out?
A: Yes for the whole Japan network. As for the South-Kanto area, observations are made for 6 hours a day.
Q: Do you have a plan to install a super computer for GPS data analysis?
A: Under consideration.
Q: How about VLBI observations in the South-west islands.
A: Next year, a mobile VLBI will visit Okinawa island.
Q: What is a ground for the density of GPS receiver's distribution.
A: It is determined from the size of precursor for the South-Kanto area and from budgetary reason for the whole Japan network.
Q: Do you summarize the each GPS site's data?
A: Yes.
Q: Do you have a plan to contribute GPS data to IERS?
A: Yes.

Introduction of SLR (Teruo Kanazawa)

Stations in the world, satellite itself, and evolution of acuracy for SLR is briefly introduced.


Q: What is the lifetime of the satellite?
A: Degradation of the reflectors is the main lifetime factor. Twenty years have been past since the launch of Lageos, but the reflector is still in good condition.
Q: What is the reason for Lageos2 being launched?
A: To improve the accuracy by increasing the spatial coverage.

Current Status of VSOP (Hisashi Hirabayashi)

Current status is introduced.


Q: How about foreign project for space VLBI?
A: There is the Radioastron project of Russia. The satellite is scheduled to be launched in 1997, but there is a possibility that this will not take place. In addition, there is a plan proposed to NASA.

Status Report of Geodetic Observations in Antarctica (Kazuo Shibuya)

There is no progress for the Antactic VLBI project. GSI made absolute gravitational measurements. DORIS is installed at Syowa station and working well. A campaign observation promoted by Germany was carried out from January 20 to February 10, 1995.


Q: Is there any fixed GPS station at Syowa station?
A: No. A pillar for a fixed station is under the construction.
Q: What is the accuracy of DORIS results?
A: +/- 2cm for each component.
Q: Are the results included in IERS?
A: From now on.
Q: Do you have detailed information concerning the 9-m antenna at Macmurdo station, especially concerning installation of the VLBI system?
A: At the moment there is no plan to install a VLBI system.
C: GPS or DORIS will detect the plate motion of Antactica for the first time.

Status Report of Borehole Observations at National Research Institute for Science and Disaster Prevention (Yoshimitsu Okada)

Eearthquake activity in the Kanto area has been low for sixty years since the big Kanto earthqukae. However M4-class earthquakes began to occur recently. Borehole observations are very useful to monitor small-magnitute earthquakes in the Tokyo metropolitan area covered with thick loam. Four 3000m-depth and twelve-2000m depth boreholes are now instrumented.


Q: You say that daytime observation is often affected by blasting. Is it possible to remove these effects from the data?
A: Yes. We actually remove such effects from the data.
Q: How small does the noise become at 3000m depth in a borehole?
A: About 1/200.
Q: Do you have a plan to deploy borehole observation system to cover the whole of Japan?
A: No.
Q: What is the cost of a 3000m depth borehole.
A: About two billion Yen.
Q: Is interferometry technique applicable for seismic waves?
A: Array of seismographs at a point is already utilized for observation. However, interferometry is difficult since the wave-form itself usualy varies between distant stations.
Q: How do you relate the borehole observationss to prediction of earthquakes?
A: We detect small earthquakes considered as precursors of big earthquake.

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