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ON GRAVITY STANDARDISATION AND THE UNIFIED EUROPEAN GRAVITY REFERENCE NETWORK UEGN02

ON GRAVITY STANDARDISATION AND THE UNIFIED EUROPEAN GRAVITY REFERENCE NETWORK UEGN02 Gerd Boedecker Bavarian Academy of Sciences and Humanities / BEK Alfons-Goppel-Str. 11, 80539 München, Germany boe@bek.badw-muenchen.de.

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ON GRAVITY STANDARDISATION AND THE UNIFIED EUROPEAN GRAVITY REFERENCE NETWORK UEGN02

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  1. ON GRAVITY STANDARDISATION AND THE UNIFIED EUROPEAN GRAVITY REFERENCE NETWORK UEGN02 Gerd Boedecker Bavarian Academy of Sciences and Humanities / BEK Alfons-Goppel-Str. 11, 80539 München, Germany boe@bek.badw-muenchen.de Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  2. ON GRAVITY STANDARDISATION AND THE UNIFIED EUROPEAN GRAVITY REFERENCE NETWORK UEGN02 • Outline of presentation: • Uses of gravity • Need for standardisation • Gravity meters • Gravity reference networks > UEGN02 • System view Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  3. Gravity uses and need for standardisation >> Homogeneity, stability Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  4. Meaning of Gravity Reference “Reference” : Connect user observation to a reliable quantity >> Connect user observation to some convention, > Comité International de Poids et Mesures > Meter Convention > BIPM (www.bipm.org), executing body: „Its mandate is to provide the basis for a single, coherent system of measurements throughout the world, traceable to the International System of Units (SI). This task takes many forms, from direct dissemination of units (as in the case of mass and time) to coordination through international comparisons of national measurement standards (as in electricity and ionizing radiation).“ Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  5. International System of Units (SI) SI-base quantities and base units: length m,mass kg, time s, electric current A,thermodynamic temperature K, amount of substance mol, luminous intensity cd Derived quantity and unit: acceleration [m s−2] Derived quantity and unit with special name (within SI): force [newton], [N]: [kg m s−2] Derived unit (not within SI), : Gal, mGal: 1 [mGal] =1 [10-5 ms-2] Note: Gravity: acceleration [m s-2] and/or specific force [N kg-1] because [N kg-1] = [kg m s−2kg-1] = [m s-2] “Metrology is the science of measurement, embracing all measurements, made at a known level of uncertainty, in any field of human activity.” Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  6. Approaches for realisation of gravity reference - depending on observation instrumentation: Satellite methods? > Resolution >>100 km, no point values > This discussion restricted to terrestrial gravimetry including marine & airborne > Will provide ground truth to satellite methods Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  7. Relative Spring Gravimeters: Examples Burris, Scintrex, LCR Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  8. g = -a +f Airborne gravimetry Platform scalar → Strapdown vector ↓ Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  9. Absolute gravimeters: Examples: Potential reference instruments > m, s BKG, BEK FG5, A-10 Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  10. Absolute gravimeters: Recent developments J.E. Faller: Cam-Driven Absolute Gravimeter J.E. Faller, A.L. Vitouchkine 2004 3 drops/sec Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  11. Absolute gravimeters: Future Atom Interferometer http://www.iqo.uni-hannover.de/ertmer/casiindex/ Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  12. Approaches for realisation of gravity reference - depending on historical evolution: Summary ~>1800 Pendulum, absolute? / relative <~1890 Vienna System ~>1910 Potsdam System ~>1930 Relative spring gravimeters ~>1970 Absolute free fall gravimeters ~>1970 IGSN71 various base networks, national & global contribution of absolute obsns. increasing ~>2010 Atom interferometer (absolute) Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  13. Approaches for realisation of gravity reference - as to base networks: Conventional approach: Few Absolute Obervations N-S Calibration Lines E-W Gravity Changes Monitoring Example: IGSN71 Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  14. UEGN94 Gravity base networks in Europe ~2000 Focus on national base networks Some international projects: Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  15. UEGN02 (Unified European Gravity Reference Network 2002) Past European Subcommission of the IGGC Recommendation: Unification of Gravity Reference Networks ! During IAG2001 Scientific Assembly in Budapest : Decision for new European Gravimetric Reference Network Participating countries: Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  16. UEGN02 Project Characteristics: Very Diverse Network Types Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  17. UEGN02Adjustment Model applicable to inhomogeneous data Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  18. Major Challenge: Outliers • Problems show up as outliers, > divers causes: • Wrong station identification • Wrong height identification • Wrong date / time (>wrong tidal correction) • Model deficiencies for non-standard cases: • Periodic errors of relative meters • Non-linear drifts under stress, e.g. quick height changes • Bad reliability • >> Conclusion: No automatic error analysis and • no decision making based on • purely mathematical methods! • >> SUPPORT HUMAN ANALYSIS and INTERFERENCE • by providing optimal • Information selection & preparation • Visualisation • Interaction & GUI, e.g. drop observation Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  19. GUIs to trace problems Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  20. UEGN02 Project Characteristics • UEGN02 Gravity Reference Networks Characteristics • 1756 Stations in 16 countries • Very different network structures: • Sometimes weak reliability • Data Characteristics • 34744 observations incl. 507 absolute observations • 51 instruments (incl. different status of same instrument) • Many observers • Different observation procedures • >> Heterogeneous data sets • Homogeneous tidal reduction (Olivier Francis, ECGS Luxembourg) • Adjustment Characteristics • Adjustment model flexible 10082 parameters (incl. offsets, drifts, calibration factors) • Parameter solution; inversion only occasionally • Weight iteration for relative observation series • International Cooperation ! Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  21. Sample Problem Example: Manual obsns canceling CH: Version 1: CH 24 cancellations, Version 2: Boe 23 consecutive cancellation of biggest residual > 50 μGal Biggest station gravity value change 47μGal at station with one sided tie, many about >10 μGal Many similar situations > time consuming! Procedure developed o.k., but problem for big number! For relative reference ties, take >3 relative meters carefully studied for systematic effects! Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  22. UEGN02 Results Overview Relative obsns: 34237 Absolute obsns: 507 Stations: 1756 Parameters: 10082 Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  23. UEGN02: Conclusions • Achievements • Extended homogeneous gravity reference network • Mutual control across border, increased accuracy • Homogeneous treatment – tides, adjustment model • UNIGRACE – embedding now complete • Common data treatment • > analysis, comparison and optimisation of procedures • Common European infrastructure • Lessons learnt for future works • Improve standardisation of absolute & relatvie obsns. • Promote light absolute meters (e.g. A-10, cam-driven) • Be most careful at manual fieldbook, station identity • Probably last base network of this type Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  24. Absolute Meter (~FG5) Relative Absolute (~A10) Relative Meter Absolute (~FG5) Supercond. Absolute Meter (~A10) Gravimetry Performance Gravimetry Costs System View on Gravity Reference Networks: System: { Gravity Meter | Station} Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  25. Groundwater Atmosphere Tides Unknown Masses Field Gravity Station (Min Standard Info) Reference Gravity Station (Max Standard Model Info) (Local SG Obsns.) Station Performance + Sup.Cond. + FG5, 1/a + Local Env. Mod. Environm.Mod. Station Costs System View on Gravity Reference Networks: System: { Gravity Meter | Station } Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  26. LocEnvMon LocEnvMon LocEnvMon LocEnvMon LocEnvMon LocEnvMon LocEnvMon LocEnvMon LocEnvMon LocEnvMon LocEnvMon LocEnvMon 3000 km Zero Order Reference 50 km Field Survey Reference LocEnvMon Local Gravity Monitoring Dedicated Gravity Reference Network Types: Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  27. Sample Project New Gravity Base Network Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  28. „Gravity standards / base networks“ Relative meter SI Base standards & Intercomp. Absolute meter Ref. Relative meter Gravity Reference Networks e.g. UEGN02 Ref. User gravity Absolute meter Reference User gravity Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

  29. „Gravity standards / base networks“ • Conclusions • Viewpoint of standardisation increased • Role of absolute meters will increase with ease of use • Networks will persist for a few decades • More attention on field procedures! Thank you ! Prag – GEOS, 2008 – 2 - 27…28 ‚Gravity Standardization & UEGN02 ‘ Gerd Boedecker

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