Establishment of a Global Absolute Gravity Network

Transcription

1 Establishment of a Global Absolute Gravity Network H. Wilmes 1), H. Wziontek 1), R. Falk 1), J. Ihde 1), S. Bonvalot 2), R. Forsberg 3), S. Kenyon 4), L. Vitushkin 5) 1) Federal Agency for Cartography and Geodesy (BKG), Germany 2) Bureau Gravimétrique International (BGI), France 3) Danish National Space Center (DNSC), Denmark 4) National Geospatial-Intelligence Agency (NGA), U.S.A. 5) All-Russian D.I.Mendeleev Institute for Metrology (VNIIM), Russia

2 Gravity reference networks Present IAG gravity reference still is the IGSN71 with station accuracies of 1 µm/s² ( 100 µgal) IGSN71 reference network (after Morelli) Adopted 1971, XXV. IUGG Gen. Assembly Moscou Observations: 10 AG pendulum relative gravity Fixed the Potsdam datum correction of -14 mgal 2

3 Gravity reference networks In 1971 Levallois proposed to establish a global absolute gravity network. IAG Special Study Group 3.87 Realisation of IAGBN Boedecker and Fritzer (1986): International Absolute Gravity Basestation Network IAGBN (A) (after Boedecker) 3

4 Distribution of absolute gravimeters Complemented by other instrument types: e.g. JILA-G, A10, IMGC, GABL, Sakuma, Faller, etc. and the new atom interferometers Owners: Metrological, Geodetic, Geologic and Geophysical institutions 4

5 Where do the requests come from? Metrology: global precise gravity reference system Based upon SI-standards, consistent, long-term available Global height system realisation, monitoring of height changes Satellite gravity field missions and geoid determination Observations of global change processes Investigations of mass changes, for the Earth body, hydrosphere, atmosphere, centre of mass investigations Connection with geometric observations GNSS, SLR, VLBI, DORIS, precise levelling, tide gauge measurements... Purely geometric observations include low-order gravity field parameters in tracking network evaluation GGOS 5

6 The GGOS Idea GGOS is the Global Geodetic Observing System of the International Association of Geodesy (IAG). Observations of the three fundamental geodetic observables and variations, Earth's shape, Earth's gravity field, Earth's rotation Built upon IAG Services (IGS, IVS, ILRS, IDS, IERS, IGFS, etc.) GGOS requests : To ensure the consistency of geometric and gravimetric products To guarantee clear and consistent standards and conventions for geometry and gravimetry Access to gravity data via metadata 6

7 Gravity variations at selected reference sites Bad Homburg BH Wettzell WE Medicina MC Schwerevariationen [nm/s^2] Gravimetric residuals after combining AG and SG for the sites Bad Homburg (D), Wettzell (D), Medicina (It) -150 Jan 2002 Jan 2003 Jan 2004 Jan 2005 Jan 2006 Jan 2007 Zeit 7

8 Gravity variations at selected reference sites TIGO Concepción (Chile), combined gravity residuals of SG-38 and FG5-227 (corrected for SG-drift, tides, air pressure and polar motion) 15 g [µgal] Jan. 05 Jul. 05 Jan. 06 Jul. 06 Jan. 07 Example for strong gravity variations at the geodetic reference station Concepcion (Chile) 8

9 Common standards All observations refer to SI units Absolute gravimeters need to be compared international level ICAG, four-yearly regional RICAG, intermediate times Processing standards for the data evaluation and corrections IAG resolutions IERS standards Conventions about models and parameters to be corrected in a common way GUM standards Agreed evaluation methods 9

10 Which data are presently available? National Geospatial Intelligence Agency (NGA), USA) Source: S. Kenyon Most of the observations are related to cooperation with other national institutions. 10

11 Example of absolute gravity networks Federal Agency for Cartography and Geodesy (BKG), Germany Observations period Observations with FG5 and A10 absolute gravimeters 11

12 Gravity reference networks in specific regions Example: Absolute Gravimetry in Antarctica Source: Amalvict et al., 2006 Absolute gravity observation by various groups on the African plate Source: Mäkinen et al., EGU 2009 Further observations with regional focus: NKG Working Group, ECGN, Japan, China,... 12

13 Registry based upon AGrav Database Web-based database Absolute gravity database is part of the BGI services Realization on two mirror servers at BGI and BKG Standardised data upload with project files 13

14 AG Database - AGrav Implementation and test phase of the database complete At present 26 instruments 419 AG stations 1339 AG observations

15 Global Geodynamics Project (GGP) Global Network Absolute Gravity Sites in Agrav Database Network of Superconducting gravimeters 15

16 Realisation of a global gravity reference system The network consists of globally distributed stations marked on the Earth body which are repeatedly observed with AG Time-dependent gravity variations are taken into account AG participate in international comparisons (ICAG) every 4 years, and in regional comparisons (RICAG) after 2 years All stations include geometric sensors (permanent GNSS and others) Selected stations are equipped with a Superconducting Gravimeter (cooperation with the GGP-Service); facilities for AG comparison Selected stations connected to tide gauges Registry (information and data system) may use AGrav database Models and corrections must be agreed and fixed New AG reference system replaces IGSN71 (100 µgal-level) New gravity reference system can reach the few µgal-level 16

17 Conclusions Replacement of IGSN71 is overdue Proposed realisation of a global absolute gravity reference system at the few µgal-level Modern AG instruments with worldwide distribution have the capabilities; regular calibration / comparison necessary Some of the sites should coincide with the ICAG or RICAG sites AGrav database will support the realisation of the new gravity reference system Reference network realises the connection with GNSS, superconducting gravity and tide gauge sites Next step: Preparation of a Call for Participation Your contribution is required! 17

18 Thank you for the attention! 18