I . SLR ACTIVITIES

The Chinese SLR Network consists of 5 fixed stations located in Shanghai, Changchun, Beijing, Wuhan and Kunming and 2 Mobile systems, namely CTLRS and CROS (Yang, 2001). The characteristics of the Chinese SLR stations are listed in Table 1. The active-passive mode-locked Nd:YAG lasers (100 mj, 200 ps) are used in Changchun, Beijing and Kunming, and the SFUR mode-locked Nd:YAG lasers (30 mj, 50 ps) are adopted in Shanghai, Wuhan, CTLRS and TROS. Except CTLRS, all stations are equipped with C-SPAD receivers, which have some advantages: single photon sensitivity, large dynamic range for return signals, low time jitter, compact and rugged design. All stations have the HP58503A GPS time and frequency receivers. Most of above-mentioned instrumentation were supported by the national project “the Crustal Movement Observation Network of China” and installed at the stations since 1997.

The single-shot ranging precision for Lageos for Shanghai, Changchun, Beijing and Wuhan is about 12-20 mm, and 20-30 mm for Kunming and the mobile systems. Shanghai Station developed a multi-satellite alternate tracking and control system and can easily switch tracking of space objects within 20 seconds. The Shanghai Station has daylight tracking capability (Yang, 1999).

Table 1.  Characteristics of the Chinese SLR Stations (2002)

 

Note:   7837  Shanghai Observatory, Chinese Academy of Sciences

7237  Changchun Satellite Observatory, Chinese Academy of Sciences

7249  Chinese Academy of Surveying and Mapping (Beijing)

7231  Institute of Geodesy and Geophysics, Chinese Academy of Sciences (Wuhan) and Institute of Seismology, the State Bureau of Seismology (Wuhan)

7820  Yunnan Observatory, Chinese Academy of Sciences(Kunming)

CTLRS  Xi’an Institute of Surveying and Mapping

TROS  Institute of Seismology, the State Bureau of Seismology (Wuhan)

The satellite laser ranging experiment with sub-centimeter single-shot precision was carried out at Shanghai Observatory in collaboration with the Czech Technical University. A portable Pico Event Timer and independent data acquisition and processing software package was brought to Shanghai and was operated in parallel to the existed SLR system and has tracked 10 passes satellites which have better distribution of retroreflectors with 7-8 mm single shot precision during August 16-22, 2001. No obvious biases were detected in the experiment.

Changchun Station has good weather and has achieved the requirements of a standard station both in data quality and quantity as issued by ILRS. The system biases for most of the stations are of serious concern, thus the calibration techniques and local surveys are carefully investigated.

The mobile system TROS was moved to Urumqi, the biggest city in the northwest border and had tracked 44 passes of Lageos from April 23 to June 5, 2001. Afterwards, the TROS was moved to Lhasa, Tibet in June 2001, and left in January 2002. It had obtained 102 passes from Lageos and 129 passes from other satellites.

The operation center and data center for the Chinese SLR Network have been set up at Shanghai Observatory. For almost twenty years, the Shanghai Observatory has pursued the high precision processing of SLR data for many geodetic and geophysical investigations. Shanghai Observatory developed the software package SHORDE (Shanghai ORbit DEtermination), which has been used for the analysis of SLR data since 1982. Since September 1999, Shanghai Observatory has published the Lageos data analysis report for the global stations every week at web site: http://center.shao.ac.cn/APSG/Newsletter/index.htm  Shanghai Observatory is acting as an associate analysis center within the ILRS (Feng, 2000).

There is a new cooperation agreement between the National Astronomical Observatories, Chinese Academy of Sciences and San Juan Observatory, Argentina. A new fixed SLR station will be installed at San Juan Observatory by 2003. The plan is supported by the Ministry of Science and Technology, China. The characteristics of the SLR system will be the same as the Beijing Station.

II.  VLBI ACTIVITIES

There are two 25-m fixed radio telescopes working for VLBI observations in China. One is at Sheshan near Shanghai and the other at Nanshan near Urumqi. During last four years, the receivers and recording terminals have been improved. The VLBA and MKIIIA terminals of the above stations have been upgraded to MKIV in 2000.

The parameters of the receivers at both stations are listed in Table 2. The two VLBI stations are the members of European VLBI Network (EVN) and International VLBI Service (IVS) for Geodesy and Astrometry (Hong, 2002).

Table 2.  VLBI Receivers of Sheshan and Nanshan Stations

A mobile VLBI system with a 3.5-m antenna has been developed by Xi’an Institute of Surveying and Mapping in collaboration with the Shanghai Astronomical Observatory in 2000. The mobile system dedicates for the geodetic research and settled down in Kunming since 2000. It has S/X-band receivers and a S2 recording terminal.

The above-mentioned two 25-m and one 3.5-m antennas combine into a VLBI network in China, which is used for monitoring the crustal deformation.

The Shanghai VLBI correlator has been developed since 1995 and the first fringes of astronomical observation data were obtained in 2000. The correlator is a two-station FX mode one. A plan for developing a 4-station correlator with a disk array and real time VLBI experiments is under consideration.

The research of VLBI applications in geodesy and geodynamics has been done by Li Jiling, Wang Guangli, et al. of Shanghai Astronomical Observatory. They worked on the new polar motion series (Li, 2000), global solution of VLBI observations (Li, 2000), the statistical selection of on-plate sites (Li, 2001), the VLBI experiments and data analysis during the campaigns of the Asia-Pacific Space Geodynamics (APSG) project from 1997 to 2000 (Wang, 2002).

REFERENCES

[1] Feng Chugang, Yang Fumin and Zhu Yuanlan, 2000, Lageos-1 and Lageos-2 quick-look residual analysis, Proceedings of 12th International Workshop on Laser Ranging, Matera, Italy.

[2] Hong, X.Y., Zhang, J., Zhang, X.Z., 2002, VLBI facilities and observations in China, Acta Astronomica Sinica, Special issue (in press).

[3] Jinling Li, Bo Zhang, Ming Zhao and Guangli Wang, 2001, A statistical selection of on-plate sites based on a VLBI global solution, Earth Planets Space, 53: 1111-1119.

[4] Li, J. and Wang G., 2000, Global solution of VLBI observations and assessments, Earth Planets Space, 52, 731-733.

[5] Li Jinling and Wang Guanli, 2000, An analysis of the polar motion series from VLBI observations, Chinese Science Bulletin, 45(21): 1945-1948.

[6] Wang Guangli, Li Jinling and Qian Zhihan, 2002, APSG VLBI experiments and the results, Chinese Journal of Geophysics, 45, Suppl, 1-4.

[7] Yang, Fumin, Xiao, Chikun, et al, 1999, Design and observations of the satellite laser ranging system for daylight tracking at Shanghai Observatory, Science in China, Series A, 42(2): 198-206.

[8] Yang Fumin, 2001, Current status and future plans for the Chinese Satellite Laser Ranging Network, Surveys in Geophysics, 22: 465-471.