International Association of Geodesy 2-Feb-16 1 The Role of the GPS/GNSS in Geodesy and Geodynamics 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 Doubletree Hotel, 1515 Rhode Island Avenue, Washington, D.C October 4-5, 2007 International Association of Geodesy 2-Feb-16 2 The Role of the GPS/GNSS in Geodesy and Geodynamics International Association of Geodesy (IAG) and Space Age The International GNSS Service (IGS) History and Development Scope and Products I GPS Service I GNSS Service IAG/IGS Expectations concerning different GNSS International Association of Geodesy 2-Feb-16 3 Geodesy and the Space Age Geodesy is based on and provides information for geometry and kinematics of/on Earth and in its environment, Earth orientation and rotation, and The Earths gravity field including its variability. It is thus necessary to define, realize and maintain unique reference systems on Earth and in the sky, and to monitor the transformation between them. The space age brought a revolution in geodesy and led to the creation of four important services, 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. International Association of Geodesy 2-Feb-16 4 Space Geodesy: GNSS GPS GPS: USA, about 30 satellites in 6 planes GLONASS: satellites in 3 planes GLONASS GALILEO: one test satellite (GIOVE A) in orbit GALILEO Densification of ITRF, high resolution ERPs, enabling atmosphere and gravity field determination International Association of Geodesy 2-Feb-16 5 IGS: International GNSS Service The creation of the IGS was initiated in 1989 with I.I. Mueller, G. Mader, B. Melbourne, B. Minster and Ruth Neilan as protagonists The IGS became an official IAG service in The IGS first was a pure GPS Service, it became the International GNSS Service in Today the IGS truly is an 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 standing for continuity and leadership. International Association of Geodesy 2-Feb-16 6 IGS Development In 1992 the IGS was based on about 20 geodetic receivers, 400+ receivers are active and their data retrievable today IGS Network in 2007 Monitor station motion in real time International Association of Geodesy 2-Feb-16 7 IGS Products In 1992 the IGS started off as an orbit determination service (dm accuracy) for about 20 GPS satellites. Today, the IGS provides ephemerides (accuracy of 2-4 cm) for about 30 GPS satellites and for GLONASS satellites, i.e., for all active GNSS satellites. In addition the IGS provides invaluable archive of 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. International Association of Geodesy 2-Feb-16 8 IGS enabling great science The new age of gravity field determination was initiated with the launch of CHAMP in July GRACE, launched in 2002, explores the use of inter-satellite mea- surements (1-d-gradiometer) to study the time variability of the gravity field, GOCE will make use (starting 2007) of the 3-d-gradiometer to derive the best possible stationary gravity field. CHAMP GOCE GRACE A and B GNSS/IGS-derived positions con- tribute to gravity field estimation! (lower degree & order harmonics) International Association of Geodesy 2-Feb-16 9 IAG/IGS Expectations concerning GNSS The scientific community will not switch from one GNSS to another, but combine the measurements from all systems (the IGS is already doing that with GPS and GLONASS). It is assumed that at least the same information as for GPS today will be openly (without fees) available for all GNSS and made available by the same receivers. The obvious advantages of combining GNSS are: With n different GNSS the common parameters shoud at least improve by a factor of n 1/2... Inconsistencies in the reference frames cannot occur. System-specific systematic errors may be detected more easily (and hopefully removed). Better coverage for atmosphere sounding applications International Association of Geodesy 2-Feb IAG/IGS Expectations concerning GNSS The GNSS constellations differ considerably Different systems improve the geometry, help to understand systematic errors. July 7, 2006: sub-satellite tracks of: GPS G06, daily repeat orbit and GLONASS R06, repeating after 8 days. International Association of Geodesy 2-Feb IAG/IGS Expectations concerning GNSS In order to be really useful for science the GNSS system providers should make available the full technical information concerning the space segment and the signal structure, including Offsets/patterns of antenna phase centers of satellites transmitting antennas w.r.t. satellites center of mass Information related to the satellites attitude. Information to generate an a priori radiation pressure model of good quality SLR reflector arrays and corresponding information (including offset w.r.t. CoM) International Association of Geodesy 2-Feb IAG/IGS Expectations concerning GNSS The scientific community, organized in IAG, will do its best to exploit the full potential of all Global Navigation Satellite Systems by combining the measurements of all systems in the same analysis stemming from combined GPS/GLONASS/GALILEO receivers. This kind of analysis is already performed by the IGS for GPS and GLONASS, where the number of observations is not at all balanced The IGS provides leadership in the scientific exploitation of the GPS and other GNSS since more than 15 years. This IGS role should be acknowledged and the US/GPS contri- bution to the IGS strengthened through the PNT Advisory Board. International Association of Geodesy 2-Feb IAG and its Services Monitoring global geodetic / geophysical phenomena is a difficult task. In IAG such tasks are handed over to so-called Services. IAG is willing to establish a service, provided there are clearly defined products and an important scientific user community. The space age generated a revolution in geodesy and led to the creation of four relevant services, International Earth Rotation Service (IERS) in 1989 IGS (International GPS Service) in 1991/1994 ILRS (Intl. Laser Ranging Service) and IVS (Intl. VLBI Service) around the end of the 20 th century. International Association of Geodesy 2-Feb GNSS contributions to Science and Society The GNSS/IGS support Earth science & society by providing accurate satellite orbits for all GNSS satellite and (selected) receiver clock corrections for all GNSS The GNSS/IGS contribute and give (will give) easy acces to the International Terrestrial Reference Frame (ITRF) The GNSS/IGS relate GNSS-specific systems like WGS-84, PZ-90 and will relate the corresponding GNSS system times on the sub-nanosecond level. The GNSS/ IGS monitor Earth orientation and -rotation with daily resolution. The GNSS/ IGS monitor the Earths ionosphere with two-hours time resolution. The GNSS/ IGS help enabling modern gravity field determination & monitoring. International Association of Geodesy 2-Feb Space Geodesy: Laser Ranging... SLR provides the origin of the terrestrial system, it contributes to the scale, Earth rotation, calibrates/validates GNSS orbits. The ILRS (International Laser Ranging Service) provides mea- surements and products International Association of Geodesy 2-Feb Space Geodesy: VLBI VLBI provides in addition precession, nutation and UT1, and contributes to scale of the terrestrial network. Celestial reference frame is established by VLBI. International Association of Geodesy 2-Feb The IGS as an Official Service Orbit consistency between 1994 and 2007 (mm per coordinate) of individual AC solutions w.r.t. combined product reaches 1cm level, the satellite clock consistency a level of 0.05 ns International Association of Geodesy 2-Feb Monitoring Polar Motion The Earths pole moves in bad circles of slowly varying radius around the Earths figure axis (once in 430 days=Chandler period). Polar motion monitored by the IGS between 1993 and Diameter of figure about 7m, accuracy of daily estimates