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The Global Geodetic Observing System and the IVS Service Markus Rothacher

The Global Geodetic Observing System and the IVS Service Markus Rothacher GeoForschungsZentrum Potsdam (GFZ) Fourth IVS General Meeting January 9-13, 2006, Concepción, Chile. GG S. Motivation Vision and Objectives of GGOS GGOS Structure International GGOS Activities

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The Global Geodetic Observing System and the IVS Service Markus Rothacher

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  1. The Global Geodetic Observing System and the IVS Service Markus Rothacher GeoForschungsZentrum Potsdam (GFZ) Fourth IVS General Meeting January 9-13, 2006, Concepción, Chile GG S

  2. Motivation Vision and Objectives of GGOS GGOS Structure International GGOS Activities Contributions of IAG Services (IVS) on 4 levels: First Level: Raw Data Collection Second Level: Three Pillars of Geodesy Third Level: Integration/Combination Fourth Level: Modeling/Interpretation Conclusions Contents

  3. Helplessness in the face of natural disasters demonstrates that our knowledge of the Earth’s complex system is rather limited. Deeper insight into the processes and interactions within this system is one of the most urgent challenges for our society. To monitor changes in the Earth system and the processes causing natural disasters a global Earth observing system has to be established; GGOS = geodetic part of the system. IAG Services: space geodetic techniques (VLBI, SLR/LLR, GNSS, DORIS), altimetry, InSAR, gravity missions, in-situ measurements etc. allow the monitoring of the Earth system with an unprecedented accuracy (10-9) Motivation

  4. Mission of GGOS as an IAG-Projekt Mission: • To collect, archive and ensure the accessibility of geodetic observations and models; • To ensure the robustness of the three fundamental fields of geodesy: geometry, orientation, and gravity; • To identify a consistent set of products and establish requirements concerning its accuracy and reliability; • To identify IAG service gaps and to close them;to stimulate close cooperation between IAG services; • To promote and improve the visibility of the scientific research in geodesy; • To achieve maximum benefit for the scientific community and society in general. http://www.ggos.org

  5. Proposed Structure of GGOS 2006-2007 Structure until new Terms of Reference officially adopted at IUGG/IAG Meeting 2007 Perugia • GGOS Steering Committee: Chair: M. Rothacher; Co-Chairs: R. Neilan, H.-P. Plag; Represented: all services, commissions, … • GGOS Executive Committee: Chair, Co-Chairs, 3 SC members • GGOS Science Panel: Science rationale, overall goals, vision • GGOS Working Groups • GGOS Secretariat • IAG Services • IAG Commissions • GEO Representatives GGOS Retreat February 15-17, 2006, in Munich; formal approval by the IAG EC, EGU Meeting, April 2006, in Vienna

  6. GGOS International Activities (1) Goals: • Contribute to the international/interdisciplinary efforts to establish a global Earth Observing System • Increase the visibility of geodesy • Establish international relationships, funding mechanisms GEO and GEOSS: • GEO = Group on Earth Observation; members are organizations and groups of organizations • GEOSS = Global Earth Observation System of Systems; Members: Contributing Global Earth Observing Systems • IAG has become a member of GEO represented by GGOS (representatives: Markus Rothacher, Ruth Neilan) • Significant contributions to the GEOSS 10-year plan

  7. GGOS International Activities (2) IGOS-P: • IGOS-P = Integrated Global Observation Strategy Partnership • Members of IGOS-P: ICSU, UNESCO, UNEP, IOC, WMO, GCOS, GOOS, GTOS, CEOS, … • GGOS will soon become an official member of IGOS-P (positive discussion at IGOS-P Meeting, November 17, 2005) • Prepare the theme „Earth System Dynamics“ for IGOS-P for meeting in May 2006 • Other themes are: • Geohazards • Integrated Global Water Cycle Observatio • Atmospheric Chemistry • Coasts (including Coral reefs) • …

  8. IERS: International Earth Rotation and Reference Systems Service IGS: International GNSS Service IVS: International VLBI Service ILRS: International Laser Ranging Service IDS: International DORIS Service IGFS: International Gravity Field Service BGI: Bureau Gravimetrique International IGeS: International Geoid Service ICET: International Center for Earth Tides ICGEM: International Center for Global Earth Models PSMSL: Permanent Service for Mean Sea Level IAS: International Altimetry Service (in preparation) BIPM: Bureau International des Poids et Mesures IBS: IAG Bibliographic Service IAG Services: Backbone of GGOS

  9. The IAG Services Global Geodetic Observing System (GGOS) Geometry Gravity IERS IGFS IGS IVS BGI IGeS ILRS IDS ICET ICGEM Sea Level Others PSMSL IAS BIPM IBS

  10. GGOS: Measuring and Modeling the Earth‘s System Measuring Information about Earth System Geometry Station Position/Motion, Sea Level Change, Deformation Space Geodetic Techniques VLBI SLR/LLR GNSS DORIS Altimetry InSAR Gravity Missions Terrestrial Techniques Levelling Abs./Rel. Gravimetry Tide Gauges Air-/Shipborne Earth System Sun/Moon (Planets) Atmosphere Ocean Hydrosphere Cryosphere Core Mantle Crust I N T E R A C T I O N S C OM B I N A T I O N Earth Rotation Precession/Nutation, Polar Motion, UT1, LOD Gravity Geocenter Gravity field, Temporal variations Observation Modelling Influence / Modelling

  11. Three major contributions: Space geodetic techniques: VLBI, SLR/LLR, GPS/GNSS, DORIS; global networks = backbone Satellite missions (altimetry, gravity, atmosphere, …) Terrestrial, airborne, shipborne measurements or campaigns (regional densification, refinement, validation, …) VLBI: Data of a global VLBI network (expensive infrastructure), correlation of the data Future: more stations (?); VLBI observations of GNSS satellites (direct link between ICRF and GNSS orbit frame) Technological innovations by VLBI2010 First Level: Raw Data Collection

  12. Satellite Missions Relevant to GGOS

  13. GEOMETRY GPS, Altimetry, INSAR Remote Sensing Leveling Sea Level REFERENCE SYSTEMS VLBI, SLR, LLR, GPS, DORIS EARTH ROTATION VLBI, SLR, LLR, GPS, DORIS Classical: Astronomy New: Ringlasers,Gyros GRAVITY FIELD Orbit Analysis Satellite Gradiometry Ship-& Airborne Gravimetry Absolute Gravimetry Gravity Field Determination Second Level: Three Pillars of GGOS VLBI contributions with darker colors

  14. International Celestial Reference Frame (ICRF), quasar coordinates (only available from VLBI) Full set of Earth Orientation Parameters (EOP: polar motion, UT1/LOD, nutation) Station coordinates and velocities Global scale: stable and absolute Atmospheric products (troposphere and ionosphere) Time/frequency products (time/frequency transfer) Level 2: VLBI Contributions to GGOS

  15. VLBI: Kinematic definition of an inertial frame (ICRF) Quasars ideal for the establishment of such a frame (ICRF) Critical: quasars are no point sources, developing with time  Very stable inertial frame from VLBI GPS: Dynamic definition of an inertial frame Stable only over a few days due to force modeling problems Good enough for short-term inertial frame ( LOD, nutation rates) Resonances between Earth Rotation and orbital periods Inertial frame has to come from VLBI LOD and nutation rates are important contributions for short-term variations, for interpolation between VLBI experiments Quasars and Satellite Orbits (VLBI and GPS)

  16. GNSS Resonance: Orbit - Earth Rotation GALILEO

  17. GPS: Receiver and satellite antenna exhibit antenna phase center variations (different for each antenna type and mounting) Absolute GPS satellite antenna calibration is extremely difficult (determined from global solutions fixing the ITRF scale) Considerable amount of multipath especially at low elevations Scale not absolutely defined, critical variations with time Problems with station heights Scale and Antennas (VLBI and GPS) VLBI: • Pointing antenna: no problems with antenna phase center variations, only marginal multipath effects • Critical: deformation by temperature changes and gravitational sag • Very stable, almost absolute scale

  18. GPS Satellite Antenna PCVs and Offsets Estimation of satellite antenna phase center variations and offsets from global GPS solutions using absolute antenna calibrations for receivers (robot)

  19. Scale Compared to ITRF2000 (IGb00) 0.34 ppb/y 0.15 ppb/y Significantly smaller scale drift for absolute PCVs

  20. Ensure the consistency and can improve the accuracy of the resulting geodetic products Complementary use of the individual techniques to strengthen the solutions Benefits from observing instruments co-located at the same site/satellite Distinguish genuine geodetic/geo-physical signals from technique-specific systematic biases Crucial to get a more detailed view and understanding of the complexity of the "System Earth" and its geophysical processes. Level 3: Integration/Combination

  21. Steps Toward a Full Combination ITRF2000 Parameter Type VLBI GPS/ DORIS/ SLR LLR Alti- GLON. PRARE metry ICRF Quasar Coord. (ICRF) X (X) (X) Nutation X X Earth Rotation UT1 X Length of Day (LOD) X X X X X Polar Motion X X X X X X X X X X (X) Coord.+Veloc.(ITRF) Geocenter X X X X ITRF Gravity Field X X X (X) X Orbits X X X X X Gravity Field LEO Orbits X X X X Ionosphere X X X X Atmosphere Troposphere X X X X Time/Freq.; Clocks X X (X)

  22. Coordinate Time Series: Westford 30-day median

  23. Steps Toward a Full Combination ITRF2005 Parameter Type VLBI GPS/ DORIS/ SLR LLR Alti- GLON. PRARE metry ICRF Quasar Coord. (ICRF) X (X) (X) Nutation X X Earth Rotation UT1 X Length of Day (LOD) X X X X X Polar Motion X X X X X X X X X X (X) Coord.+Veloc.(ITRF) Geocenter X X X X ITRF Gravity Field X X X (X) X Orbits X X X X X Gravity Field LEO Orbits X X X X Ionosphere X X X X Atmosphere Troposphere X X X X Time/Freq.; Clocks X (X) X

  24. Combination of Polar Motion CONT’02: X/Y-Pole Combination w.r.t. IERS2000 Model 1-hour time resolution

  25. Steps Toward a Full Combination ITRF2005 (?) Parameter Type VLBI GPS/ DORIS/ SLR LLR Alti- GLON. PRARE metry ICRF Quasar Coord. (ICRF) X (X) (X) Nutation X X Earth Rotation UT1 X Length of Day (LOD) X X X X X Polar Motion X X X X X X X X X X (X) Coord.+Veloc.(ITRF) Geocenter X X X X ITRF Gravity Field X X X (X) X Orbits X X X X X Gravity Field LEO Orbits X X X X Ionosphere X X X X Atmosphere Troposphere X X X X Time/Freq.; Clocks X X (X)

  26. CONT’02: Combination UT1 (VLBI) + LOD (GPS)

  27. CONT’02: Combination UT1 (VLBI) + LOD (GPS) Formal errors of LOD from GPS grow with time Formal errors of UT1 from VLBI stay at a constant level  The long-term behavior is given by VLBI, GPS helps in the interpolation (densification)

  28. Combination of VLBI Intensive Sessions (e-VLBI) with GPS rapid products and SLR/DORIS rapid solutions Main purpose: daily EOPs available within ~ 24 hours Near-real-time monitoring of the reference frame and individual stations: Eathquakes, Tsunami, station problems, … IGS: Generation of combined SINEX files on a daily basis including EOPs and station coordinates, VLBI: Use e-VLBI for rapid generation of VLBI Intensive solutions (1hour); Intensives are observed on a daily basis SLR/DORIS: Rapid generation of daily solutions (???) Complementarity: VLBI: UT1 (and scale) GPS: Reference frame, polar motion (and LOD) SLR/DORIS: geocenter (and scale) Examples: Rapid Combined IERS Daily Products

  29. Steps Toward a Full Combination IERS2007=ITRF2007+EOP2007+ICRF2007 ? Parameter Type VLBI GPS/ DORIS/ SLR LLR Alti- GLON. PRARE metry ICRF Quasar Coord. (ICRF) X (X) (X) Nutation X X Earth Rotation UT1 X Length of Day (LOD) X X X X X Polar Motion X X X X X X X X X X (X) Coord.+Veloc.(ITRF) Geocenter X X X X ITRF Gravity Field X X X (X) X Orbits X X X X X Gravity Field LEO Orbits X X X X Ionosphere X X X X Atmosphere Troposphere X X X X Time/Freq.; Clocks X X (X)

  30. Steps Toward a Full Combination IERS2008=ITRF2008+EOP2008+ICRF2008 ? Parameter Type VLBI GPS/ DORIS/ SLR LLR Alti- GLON. PRARE metry ICRF Quasar Coord. (ICRF) X (X) (X) Nutation X X Earth Rotation UT1 X Length of Day (LOD) X X X X X Polar Motion X X X X X X X X X X (X) Coord.+Veloc.(ITRF) Geocenter X X X X ITRF Gravity Field X X X (X) X Orbits X X X X X Gravity Field LEO Orbits X X X X Ionosphere X X X X Atmosphere Troposphere X X X X Time/Freq.; Clocks X X (X)

  31. Zenith Wet Delay (VLBI+GPS) : Wettzell

  32. Zenith Wet Delay (VLBI+GPS): Kokee Park

  33. Tracking Problems at Kokee Park (1) dZWD [cm] Up [cm] Obs. Rate [%] Decorrelation of troposphere and station height problematic due to degraded tracking at low elevations

  34. Tracking Problems at Kokee Park (2) Antenna degradation (July 1996) After antenna replacement

  35. Troposphere Parameters: Comparison GPS+VLBI Mean Biases 5.3 mm -2.5 mm -0.8 mm Excluded due to large dH: HART,HARKURUM

  36. Tropospheric Gradient Time Series: Wettzell 30-day median Often good agreement, especially in the last years

  37. Steps Toward a Full Combination IERS2009=ITRF2009+EOP2009+ICRF2009 ? Parameter Type VLBI GPS/ DORIS/ SLR LLR Alti- GLON. PRARE metry ICRF Quasar Coord. (ICRF) X (X) (X) Nutation X X Earth Rotation UT1 X Length of Day (LOD) X X X X X Polar Motion X X X X X X X X X X (X) Coord.+Veloc.(ITRF) Geocenter X X X X ITRF Gravity Field X X X (X) X Orbits X X X X X Gravity Field LEO Orbits X X X X Ionosphere X X X X Atmosphere Troposphere X X X X Time/Freq.; Clocks X X (X)

  38. Clock Combination: Co-located VLBI and GPS receivers running on the same high-accuracy clock Temperature stability on the few picosecond level necessary Ideal goal: common clock parameters with just one offset to be estimated between the techniques Combination on the observation level necessary Complexer Combination (e.g. Clocks)

  39. Steps Toward a Full Combination GGOS2010 = ITRF20010+EOP2010+ICRF2010+IGRF2010 ? IGRF = International Gravity Reference Frame/Field Parameter Type VLBI GPS/ DORIS/ SLR LLR Alti- GLON. PRARE metry ICRF Quasar Coord. (ICRF) X (X) (X) Nutation X X Earth Rotation UT1 X Length of Day (LOD) X X X X X Polar Motion X X X X X X X X X X (X) Coord.+Veloc.(ITRF) Geocenter X X X X ITRF Gravity Field X X X (X) X Orbits X X X X X Gravity Field LEO Orbits X X X X Ionosphere X X X X Atmosphere Troposphere X X X X Time/Freq.; Clocks X X (X)

  40. Vision 2010: Intergation of 4 Levels into a GGOS • 2010: ca. 40 Low Earth Orbiters (LEO) • CHAMP, GRACE-A/B, GOCE • T/P, ERS-1/2, Jason-1, Jason-2, Icesat, Envisat • GPS/MET, OERSTED, SAC-C • 6 COSMIC, 3 SWARM • 20 SLR satellites • Satellite constellations 2010: ca. 600 radio sources • 2010: Dense GPS networks: ca. 10‘000 stations • 1200 Japan • 1000 Plate Boundary Observatory • 400 Europe • 29 Switzerland • 100 Hz, near real-time • 2010: ca. 90 MEO and GEO satellites • 29 GPS • 30 GALILEO • 24 GLONASS • 3 ZQSS • Augmentation systems (GEO)

  41. Fourth Level: Modeling and Interpretation GEOSPHERE Plate Tectonics, Subduc-tion,Convection,Earth‘s Core KINEMATICS OF POINTS Coordinates, Velocities ATMOSPHERE Wind, Pressure Distribution ? EARTH ROTATION VARIATIONS Polar Motion, UT1 HYDROSPHERE Ocean Currents, Ground Water Geodetic Parameters Geophysical Processes CRYOSPHERE Melting of Pole Caps, Glaciers VARIATIONS OF THE EARTH‘S GRAVITY FIELD Potential Coefficients BIOSPHERE Change in Vegetation Common effort of all Services/Commissions!

  42. Links: global time series of geodetic parameters ↔ relevant geophysical models Highly interdisciplinary task: cooperation with geophysicists / geologists, glaciologists, oceanographers, hydrologists, atmosphere physicists, … Final goal: comprehensive global Earth models that can assimilate global surface deformations, mass transport and exchange Deeper understanding of: Solid Earth processes (GIA, tectonics, Earthquakes, volcanoes, …) Ice mass dynamics and balance, sea ice Ocean circulation, mass and heat transport in the oceans Sea level change, global water cycle Atmosphere dynamics Global energy budget, global mass balance, … Additional information, e.g., from global geophysical fluids is required to separate different contributions Modeling / Interpretation

  43. IVS in special, and IAG Services in general, can contribute significantly to the monitoring and understanding of the Earth system: Stable, highly accurate reference frames for all other global observing systems and monitoring activities Many contributions to geo-hazards: Earthquakes, volcanoes, land slides, de-glaciation, sea level rise, floods, storms, global warming, tsunamis, … Integration into one observing system: GGOS, not a flood of individual, inconsistent products Not only delivery of basic products: step by step reach the level of consistent modeling and interpretation of the Earth’s processes and interactions With its unique contributions the IVS has a particularly important in reaching these goals Conclusions

  44. We are looking forward to work with all of you on this challenging endeavor ! Thank you for your attention ! GG S

  45. First GGOS Workshop in Potsdam

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