The Results in the Daily Observation in the Crustal Deformation Monitoring System in the Tokyo Metropolitan Area

Y.Takahashi, N.Kurihara, T.Kondo, H.Takaba, T.Iwata, Y.Koyama, M.Sekido, J.Nakajima, T.Gotou
Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314, Japan


M.Imae,Y.Hanado,T.Yoshino, S.Hama, H.Kiuchi, A.Kaneko, H.Kunimori, T.Miki, J.Amagai, T.Ootubo, F.Takahashi
Communications Research Laboratory
4-2-1 Nukui-kita, Koganei, Tokyo 184, Japan

1. Introduction

We have established the crustal deformation monitoring system in the Tokyo Metropolitan Area (We call this project "KSP"). Both VLBI and SLR equipment are arranged at the four stations (Kashima, Koganei at HQ in Tokyo, Miura, and Tateyama). SLR observations will be conducted always in the clear sky and 5 hour VLBI experiments will be conducted everyday. The VLBI stations of Koganei and Kashima stations were constructed and we started the VLBI observations between Kashima and Koganei. The first 24 test experiment was conducted on 29th August in 1994, and we started 5 hours experiments on every week day since 31th of January in 1995. As it is in the period for test experiments now, we conducted the VLBI observations by 56 Mbps recording mode which is compatible with Mark-III. The regular daily 5 hours experiments will be started since this autumn using 256 Mbps mode on Kashima and Koganei baseline, and the VLBI observations of 3 stations including the Miura stations will be started at the beginning of next year. Figure 1 shows the configuration of stations and the results of baseline length.

Figure 1. Configuration of KSP and the baseline length.

The results in the daily test VLBI experiments from 31th January to 6th September (in the period of about 7 months) are described as follows:

2. Station Movements

We developed the software for the baseline analysis, which are called "Takemikazuchi". The software makes the data base and it makes the baseline analysis automatically. This software also supports making the results publically available using WWW (see Section 6).

Because of the test observations, we make a baseline analysis using the other software "SOLVE" which was developed by GSFC (NASA), and we describe these results since the repeatability of these results is a little better than those by automatic analysis software.


Figure 2. Movement of Koganei station against Kashima.

Figure 2 shows the change in the distance on the Kashima-Koganei baseline, and the changes in the position of Koganei (east movement, north movement, upward movement) against Kashima station (when the position of Kashima is fixed). Table 1 shows the summary of the precision. For the horizontal movements and baseline length, the precision and repeatability are about 5mm, and the precision for the vertical movement is about 2.5cm in spite of the test experiments of 56 Mbps mode. For the regular experiments of 256 Mbps mode, the precision will become one third of these results.


   Table 1. Precision and repeatability in KSP test daily experiments.
 =========================================================================
                    Mean        Repeat-              Koganei
                    Precision   ability    ----------------------------- 
                                            Position error    Change    
                     (mm)        (mm)            (mm)        (mm/year) 
 -------------------------------------------------------------------------                    
 Baseline Length      3.2        4.6           +/-0.7       0.5+/-1.9  
 East Movement        3.4        5.2           +/-0.8      -4.4+/-2.0 
 North Movement       4.1        5.5           +/-1.0      16.7+/-2.3 
 Upward Movement     17.0       26.4           +/-3.3      25.5+/-9.1 
 =========================================================================

The position changes are described in the different methods. At first, one or several stations are fixed using the tectonic model, and the position changes in the other observed stations are obtained against the fixed stations. This method is useful to obtain the deformation of the observation net. Secondly, the movements are described for the international velocity field, such as ITRF (International Terrestrial reference Frame) or the velocity field of GSFC. Finally, the movements are described as the displacement from the plate motion. Figure 3 shows the movements of Koganei and Kashima stations. We also have the results by other experiments, which is call "MDX (Metropolitan Diamond Cross)". These experiments were conducted among Kashima 34m antenna, Koganei 3m antenna, and GSI 5m antenna since 1988 once or twice every year. We show both sets of results. Figure 3 shows these station movements. Figure 3-(a) shows the movement of Koganei station relative to Kashima station. Figures 3-(b),(c) are the movements of Koganei and Kashima stations for the displacement from North American Plate motion in the reference of the GSFC velocity field in 1993, and in the reference of the ITRF velocity field in 1993. Figure 3-(d) shows the movements in the reference of the ITRF velocity fields in 1993. Figure 3-(e) is the plate motion on the plate boundary.

In the Alaska area, the station movements for the displacement from the North American Plate motion are similar to the direction of the Pacific plate motion on the plate boundary. In the Japanese area, the movements of the Kashima and Koganei stations in both KSP and MDX experiments are similar to the direction of the Pacific Plate motion and the Philippine Sea Plate motion shown in Figure 3-(e). It is possible that the deformation is caused by the pressure of the plate motion. The movements obtained from KSP experiments are different from those from MDX experiments. Furthermore, the results appear to differ according to which velocity field is used as a reference.

In Japan, many GPS stations and several VLBI and SLR stations are observed, and the results are collected. The reference of the velocity field may become important.


Figure 3. Movement of Koganei for KSP and MDX experiments and Kashima Station movement.

3. Change in the correlated amplitudes

In KSP experiments, the correlated amplitudes are obtained everyday, and we can monitor the change of the correlated flux density for several quasars. Figures 4,5 show the change in the mean value of correlated amplitudes on the Kashima-Koganei baseline for 12 sources at X band and S band, respectively. The mean value averages the different observations for the resolution and the elevation dependency. In this test period, we do not have the calibration data, but we can estimate approximately that 0.01% correspondeds to about 0.5Jy at X band and about 0.3Jy at S band. Different changes for different sources may be caused by changes in the correlated flux density. We can monitor the continuous variation of the source flux density for unresolved center part and the burst change.

Figure 4. The change in the correlated amplitude at X band on Kashima-Koganei baseline without the correction.


Figure 5. The change in the correlated amplitude at S band on Kashima-Koganei baseline without the correction.

4. Comparison of the clock

In KSP experiments, we can monitor the clock. As we have no information concerning the internal delay in the antenna, the absolute difference of clock (Hydrogen Maser) is unknown, but the change in the clock is observed. Figure 6 shows the change in the comparison of the clock and the change in the clock rate. The reasons for the clock jump is known. The rate change means the stability for long periods.

Figure 6.The change in the clock between Kashima and Koganei stations.

5. Conclusion

We have conducted 5 hour VLBI experiments for every week day since 31 January, 1995. Though these experiments are test experiments in the 56 Mbps mode, we obtain good results and information concerning the practical errors, which are the same as the theoretical errors. From these results, we believe that we can achieve 2mm precision for the horizontal component and baseline length, and 9mm precision for the vertical component in the regular 5 hour VLBI experiments in the 256 Mbps mode, and these precisions are reduced to half for 24 hour VLBI experiments in the case of real time VLBI.

The motion of Koganei station relative to Kashima station are measured. The movements are slightly different from those inferred from MDX VLBI experiments. However, the displacement from the North American Plate motion is similar to the direction of the pressure of the plate motion on the plate boundary. The movements of the other VLBI stations, at Tsukuba and Kanozan, are also the same direction.

The indication of the station movements differens according to the velocity field that is used as a reference. It is important that the reference velocity field should be common since the comparison of the different analyses and different equipment should be not confused.

We also obtain the continuous changes in the correlated flux density in KSP experiments. These changes are useful in characterizing the burst changes of the quasar.

The KSP will be completed in next year, and we will obtain the positions of 4 stations with the precision of 2-3mm using daily VLBI and SLR. Furthermore, the real time VLBI using 256 Mbps data transfer by optical fiber cable will be started during the next year.

6. Announcement

The results of KSP experiments, which are the station movements and the correlated amplitudes, are made available using the inter-net "WWW". The station movements are the results by the automatic analysis software. The reference is the position of the Kashima station moved by the latest ITRF. When you want to see the results, URL is "http://kouma.crlgo.jp/" in English and "http://kouma.nict.go.jp/index-j.html." in Japanese. If you have some question about this service, please ask Y.Koyama in CRL (Email koyama(AT)nict.go.jp) or Y.Takahashi (Email takahashi(AT)nict.go.jp).


Updated on November 2, 1995.
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