SHESHAN CO-LOCATION SURVEY Report and results Surveyed on November 2003 Reported on December 2005 Bruno GARAYT, Stéphane KALOUSTIAN, Jim LONG, Valérie MICHEL Institut Géographique National Direction de la Production Service de Géodésie et Nivellement RT/G 62 Institut Géographique National Sheshan Co-location Direction de la Production Page 2 / 110 Survey Service de Géodésie et Nivellement Version : 1 Révision : 0 Date 31/03/2006 Table of contents TABLE OF CONTENTS...................................................................................................... 2 INTRODUCTION ........................................................................................................................ 3 ACKNOWLEDGEMENTS.......................................................................................................... 3 1. CO-LOCATION SITE DESCRIPTION ............................................................................... 4 1.1. ITRF SPACE GEODETIC TECHNIQUES .................................................................................... 5 1.1.1. SHAO IGS GPS station................................................................................................ 5 1.1.2. SLR station.................................................................................................................. 6 1.1.3. VLBI station ................................................................................................................ 7 1.2. OTHER POINTS OF INTEREST ................................................................................................ 7 1.2.1. EGNOS GPS station .................................................................................................... 7 1.2.2. Survey control points and temporary stations .............................................................. 8 2. SURVEY DESCRIPTION ..................................................................................................... 9 2.1. ORGANIZATION ................................................................................................................... 9 2.2. EQUIPMENTS ..................................................................................................................... 10 2.2.1. Instruments................................................................................................................ 10 2.2.2. Equipment and accessories........................................................................................ 10 2.3. SURVEY NETWORK AND GEODETIC INSTRUMENTS OBSERVATIONS ...................................... 11 2.3.1. Strategy ..................................................................................................................... 11 2.3.2. Observations ............................................................................................................. 12 3. COMPUTATIONS ............................................................................................................... 17 3.1. ON-SITE VALIDATION ........................................................................................................ 17 3.1.1. Survey control networks............................................................................................. 17 3.1.2. GPS........................................................................................................................... 17 3.2. GPS NETWORK ................................................................................................................. 17 3.3. VLBI R EFERENCE POINT ................................................................................................... 18 3.3.1. Precision ................................................................................................................... 20 3.3.2. Fictitious observations............................................................................................... 20 3.4. SURVEY CONTROL NETWORK ............................................................................................. 21 4. RESULTS ............................................................................................................................. 21 5. ANNEXES ............................................................................................................................ 24 RT/G 62 Institut Géographique National Sheshan Co-location Direction de la Production Page 3 / 110 Survey Service de Géodésie et Nivellement Version : 1 Révision : 0 Date 31/03/2006 Introduction The ITRF is the result of a combination of the different terrestrial reference frames provided by the four space geodetic techniques GPS, VLBI, SLR and DORIS. To perform this combination between independant reference frames, it is necessary to get some co-location sites where the various techniques are observing and whose ties have been surveyed in three dimensions. Many co-location sites have been identified and some of them have missing or inconsistent ties. Furthermore, new instruments are installed or replaced on these sites. Then, the ties with the existent techniques on the site have to be determined. In this frame, it has been decided as one of the top priorities to survey the Sheshan co-location site (China). Some of the ties at Sheshan were missing (VLBI and SLR with GPS), and the one between the VLBI and SLR points was inconsistent. This document presents the results of the Sheshan local ties survey with as many details as necessary about the observations and the computations to fully understand the content of the resulting SINEX file. Acknowledgements We would like to express our special thanks to Professor YANG Fumin and Dr. LI Jingling and all their colleagues and students from the Shanghai Astronomic Observatory (SHAO), not only for their very cooperative work in a technical and adminsitrative point of view, but also for the “extras” which made us really enjoy our stay in Shanghai and made this work a success. We would also like to express our thanks to all the people working at the Sheshan VLBI station and at the Laser station for their very warmful welcome and useful help which also contributed to the success of this work. RT/G 62 Institut Géographique National Sheshan Co-location Direction de la Production Page 4 / 110 Survey Service de Géodésie et Nivellement Version : 1 Révision : 0 Date 31/03/2006 1. Co-location site description The Sheshan ITRF site is located in Sheshan area, about 30 km southwest of Shanghai. Sheshan station is the observational base of Shanghai Astronomical Observatory (SHAO), Chinese Academy of Sciences (CAS) , where there are the main following equipments : • Very Long Baseline Interferometry (VLBI) station, with a 25 m radio telescope with a set of hydrogen masers. • Third-generation Satellite Laser Ranging (SLR) station, with a 60 cm telescope. • Global Positioning System (GPS) station. Sheshan co-location site can be divided into two main sub-sites : On one site, one can find the 25 m VLBI radiotelescope and the IGS GPS station (SHAO). The second one is the running SLR station site. It should be moved to another site within the next months or year, about 500 m further on the other site of the small hill. A local control network was set up from which the instruments were observed and tied together with terrestrial and GPS observations, including the future SLR station site. RT/G 62 Institut Géographique National Sheshan Co-location Direction de la Production Page 5 / 110 Survey Service de Géodésie et Nivellement Version : 1 Révision : 0 Date 31/03/2006 1.1. ITRF space geodetic techniques 1.1.1. SHAO IGS GPS station Global view of the antenna with the dome (JPLA model) The GPS receiver and the PC DOMES number : 21605M002 SHAO reference point SHAO mark and antenna without its dome The station reference point is a mark distinct from the antenna one. (cf annexes 5.1 and 5.2). RT/G 62 Institut Géographique National Sheshan Co-location Direction de la Production Page 6 / 110 Survey Service de Géodésie et Nivellement Version : 1 Révision : 0 Date 31/03/2006 1.1.2. SLR station DOMES number : 21605S001 Current location : building hosting the SLR telescope Global view of the telescope The SLR System Reference Point (SRP) is the point in the telescope optics where the two rotation axes intersect(cf annexe 5.3.). This reference point can not be materialized. On the new SLR site, a survey point has been tied by GPS observations and included in the survey network. It is located on the terrace roof of the building which will host the new SLR station. The point is materialized by a screw used as forced centring. The reference height is the top of this screw. DOMES number : 21605M101 Future location : global view of the site Reference point RT/G 62 Institut Géographique National Sheshan Co-location Direction de la Production Page 7 / 110 Survey Service de Géodésie et Nivellement Version : 1 Révision : 0 Date 31/03/2006 1.1.3. VLBI station The Sheshan 25-m radio telescope is an alt-az antenna run by SHAO. It has been in operation since 1987, and it is one of the five main facilities of the Chinese National Astronomical Observatory. The station is a member of the European VLBI Network (EVN), the International VLBI Service for Geodesy and Astrometry (IVS), and the Asia Pacific Telescope. DOMES number : 21605S009 Global view of the VLBI antenna The measurement data is received at the phase centre of the receiver feed horn. The VLBI reference point is generally described as the point where the two rotation axes intersect. Levelling benchmarks fixed on the VLBI