International Association of Geodesy IAG: GPS and GNSS for Science

1. International Association of Geodesy 29-Apr-12 1 International Association of Geodesy (IAG): GPS and GNSS for Science G. Beutler Astronomical Institute, University of Bern Member of IAG Executive Committee and of IGS Governing Board National Space-Based Positioning, Navigation, And Timing (PNT) Advisory Board Hilton Arlington 901 North Stafford Street Virginia 22203 October 16-17, 2008

2. International Association of Geodesy 29-Apr-12 2 International Association of Geodesy (IAG): GPS and GNSS for Science The International Association of Geodesy (IAG) Global Navigation Satellite Systems (GNSS) The International GNSS Service (IGS) Leadership Strategic engagement Future challenges General remarks concerning the activities of the 2007-2008 National Space-Based PNT Advisory Board from the IAG perspective

3. International Association of Geodesy 29-Apr-12 3 About Geodesy and IAG Geodesy is based on three pillars geometry and kinematics of/on Earth and in its environment, Earth orientation and rotation, and The Earth�s gravity field including its variability Geodesy provides the metrological basis for positioning, navigation, surveying&mapping, global change studies. IAG, the International Association of Geodesy, coordinates International activities related to the above pillars. The space age brought a revolution in geodesy and led to the creation of four services relevant for GNSS, International Earth Rotation Service (IERS) in 1989 IGS (International GNSS Service) in 1991/1994 ILRS (Intl. Laser Ranging Service) and IVS (Intl. VLBI Service) around the year 2000.

4. International Association of Geodesy 29-Apr-12 4 Active and Emerging GNSS

5. International Association of Geodesy 29-Apr-12 5 About Geodesy and IAG Since 1994 Global Navigation Satellite Systems (GNSS) play an essential role in geodesy to maintain and densify the International Terrestrial Reference Frame (ITRF, issued by the IERS) monitor Earth rotation monitor the atmosphere determine precise LEO orbits (LEO=Low Earth Orbiter) determine the Earth�s gravity field (!) In geodesy GNSS will continue to play a leading role for next 20-30 years. The IGS (International GNSS Service) is acting on behalf of IAG for the scientific exploitation of all GNSS.

6. International Association of Geodesy 29-Apr-12 6 About the IGS The creation of the IGS was initiated in Edinburgh in 1989 with I.I. Mueller, G. Mader, B. Melbourne, and Ruth Neilan as protagonists The IGS became an official IAG service in 1994. The IGS first was a pure GPS Service, it was renamed as the International GNSS Service in 2004. Today, the IGS is a truly interdisciplinary service in support of Earth Sciences and Society committed to use the data from all GNSS. Since its creation the IGS Central Bureau is located in the USA with Ruth Neilan as director � who stands for continuity and leadership.

7. International Association of Geodesy 29-Apr-12 7 About the IGS

8. International Association of Geodesy 29-Apr-12 8 About the IGS Development of the IGS combined GPS/GLONASS network (from Dach et al., 2008 IGS Workshop)

9. International Association of Geodesy 29-Apr-12 9 About the IGS In 1992 the IGS started off as an orbit determination service (decimeter accuracy) for about 20 GPS satellites. Today, the IGS provides ephemerides (accuracy of 2-4 cm) for about 30 GPS satellites and for all GLONASS satellites (<10 cm), i.e., for all currently active GNSS satellites. In addition the IGS provides archive of all globally relevant GNSS observations since 1991 satellite and receiver clock corrections (sub-ns accuracy) polar motion (PM) and length of day (lod) (cm accuracy) coordinates and velocities for 200+ sites (cm / mm/y accuracy) atmosphere information The IGS products are accurate, reliable and robust, available in a timely manner.

10. International Association of Geodesy 29-Apr-12 10 About the IGS The IGS provides leadership to the Civilian GPS/GNSS community striving for the highest achievable accuracy by studying systematic errors (case for SLR reflectors) system peculiarities (case of 30+ constellation) different GNSS and their combination to the benefit of users reaches out to the entire GNSS community by making available precise GPS GLONASS in future hopefully also GALILEO orbits and clocks in one and the same reference frame. identifies future challenges by its strategic planning

11. International Association of Geodesy 29-Apr-12 11 Case for SLR reflectors

12. International Association of Geodesy 29-Apr-12 12 Case for SLR reflectors

13. International Association of Geodesy 29-Apr-12 13 Case for SLR reflectors From: Yang Fumin(1), Chen Wanzhen(1), Zhang Zhongping(1), Wang Yuanming(1), Zhang Haifeng(1) Zhao You(2), Fan Cunbo(2) and Han Xingwei(2) (1) Shanghai Observatory, Chinese Academy of Sciences, Shanghai, China (2) Changchun Observatory, Chinese Academy of Sciences, Changchun, China

14. International Association of Geodesy 29-Apr-12 14 SLR Reflectors on GNSS Satellites SLR provides the only independent check (in the radial direction) of GNSS orbits � determined with the GNSS signals and carriers. The payload required to enable SLR tracking is minor (about 10 kg, the SLA on Compass has 2.5 kg), the costs marginal. SLR tracking to GNSS, internationally coordinated by the ILRS, was successfully performed for GPS (PRN 05 & 06) All GLONASS satellites GIOVE-A & -B (GALILEO) COMPASS-M1 (launched in spring 2007)

15. International Association of Geodesy 29-Apr-12 15 GNSS Peculiarities The GNSS constellations differ considerably (inclinations, daily vs. 8-day repeat orbits for GPS and GLONASS, respectively) Different constellations improve the geometry, help to understand systematic errors

16. International Association of Geodesy 29-Apr-12 16 GNSS Peculiarities Observing GPS and GLONASS from one site: Mean inclinations of GPS and GLONASS ore different (Dach et al., 2008)

17. International Association of Geodesy 29-Apr-12 17 GNSS Peculiarities Observing one GPS and one GLONASS satellite over ten days from two different sites (roughly) at the same latitude (Dach et al., 2008)

18. International Association of Geodesy 29-Apr-12 18 Case for 30+ Satellites PDOP (Positional Dilution of Precision): <1 : excellent, > 4 bad. Motivation (a) 30+ constellation, (b) combine systems

19. International Association of Geodesy 29-Apr-12 19 International Committee on GNSS The ICG was set up by the United Nations Office for Outer Space Affairs (UNOOSA) ICG is �A forum to discuss Global Navigation Satellite Systems (GNSS) to benefit people around the world� As opposed to the IGS the emphasis is not on scientific, but on outreach issues where system providers and users are working together. The Third Meeting of the International Committee on Global Navigation Satellite Systems (ICG) is organized by the Jet Propulsion Laboratory (Ruth Neilan), Pasadena, USA, 8 - 12 December 2008.

20. International Association of Geodesy 29-Apr-12 20 Report on PNT 2007-2008 Activities From the IAG perspective the draft report on the 2007-08 activities is already in excellent shape (in particular the Executive Summary). It is a concise summary of the Board�s 2007-08 activities and provides in itself the best argument to continue the Board�s activities. The IAG is very pleased that the case of Commitment to a 30+ constellation SLR reflectors on GPS satellites get appropriate attention and that International collaboration is viewed as an important issue.