1 AOGS 2012, Singapore, Aug 13-17, 2012 Surveying co-located GNSS/VLBI/SLR Stations In China Xiuqiang Gong, Yunzhong Shen, Junping Chen, Bin Wu Shanghai Astronomical Observatory Tongji University

2 Content  Introduction  Surveying campaign  Data processing  Results and discussion

3 Local tie  Local ties are necessary for establishment of ITRF  The Crustal Movement Observation (CMONOC)Network of China  2000 GNSS stations,4 SLR stations and 7 VLBI stations  Local-ties missing and inconsistant

4 GPS reference point Measure the instrument height using calliper accurately The ARP to RP (Antenna Phase Center) Phase center correction

5 VLBI\SLR Reference Point Defined as intersection of the telescope axis or invariant point when orientated. The constant distance from RP to the feed horn of the telescope is needed.

6 SLR VLBI SLR/VLBI Local ties of CMONOC

7 Collecting data: control network GNSS control network  align vectors into the global frame.  provide starting points for terrestrial control network Terrestrial control network: get control points for SLR/VLBI

8 Collecting data of circle

9 Collecting data: Survey Methodology

10 Data processing  GPS:Use Bernese5.2 and Gamit to solve the short baseline  Collect the coordinates of GNSS station of ITRF2008  Non-constrain adjustment of GPS network  Combined terrestrial measurement adjustment:  Disatance  Direction  Vertical angle

11 Model of 3D adjustment Distance observation: in the station local coordinate frame Where and mean Additive and Multiplication Constant Direction observation: Vertical angle observation ：

12 observational equations Transfer the coordinates from the station local coordinate frame NEU to space reference system XYZ

13 Results and comparison Vector ∆X∆Y∆Z∆N∆E∆U CHAN-SLR GUAO-VLBI SHAO-SLR SHAO-VLBI BJFS-SLR KUNM-SLR WUHN-SLR Comparison of our result with the ITRF2008 solution Value( in m) The difference of Kunming is more than 10cm ， perhaps the instruments has been moved, or the SLR coordinate in ITRF2008 is not correct since it has few even none laser observations in these years.

14 Results and comparison Vector ∆X∆Y∆Z∆N∆E∆U GPS(SHAO)-VLBI GPS(WUHN)-SLR GPS(BJFS)-SLR Comparison of our results with IGN’S in 2003(value in m) 1 The two sets of results of BJFS site are in perfect agreement with the difference less than 5mm 2 The Wuhn site also has a good agreement since the distance is 13km. 3 The difference in Shanghai is huge especially in the height coordinate up to

15 Results and comparison Comparison of the baseline difference between ITFR2008 and ITRF2000(value in m) Vector ∆X∆Y∆Z∆N∆E∆U GPS-VLBI Compare the results in ITRF2008 product and ITRF2000 ， the difference in U direction is up to Considering this ， the differences of IGN’s result and our result are only 5.5mm. Being a conclusion, we discover the fact that from 2003 up to 2011,the VLBI RP has descended about 2cm relative to the GPS RP in Shanghai where the two techniques are set in one courtyard. So it is necessary that the co-location sites especially including VLBI telescope in China should be periodically re-measured on a regular basis.

16 Thank you for your attention!