Establishment of a Global Absolute Gravity Network28.06.2010 TG-SMM-2010 – St. Petersburg, Russia...
Transcript of Establishment of a Global Absolute Gravity Network28.06.2010 TG-SMM-2010 – St. Petersburg, Russia...
1) Federal Agency for Cartography and Geodesy (BKG), Germany2) Bureau Gravimétrique International (BGI), France 3) Danish National Space Center (DNSC), Denmark4) National Geospatial-Intelligence Agency (NGA), U.S.A. 5) All-Russian D.I.Mendeleev Institute for Metrology (VNIIM), Russia
Establishment of a Global Absolute Gravity Network
H. Wilmes1), H. Wziontek1), R. Falk1), J. Ihde1), S. Bonvalot 2), R. Forsberg 3), S. Kenyon 4), L. Vitushkin 5)
TG-SMM-2010 – St. Petersburg, Russia
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Gravity reference networks
Present IAG gravity reference still is the IGSN71with station accuracies of 1 µm/s² ( 100 µGal)
IGSN71 reference network (after Morelli)
• Adopted 1971, XXV. IUGG Gen. Assembly Moscou
• Observations: 10 AG1.200 pendulum24.000 relative gravity
• Fixed the Potsdam datum correction of -14 mGal
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Gravity reference networks
IAGBN (A) (after Boedecker)
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”
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Distribution of absolute gravimeters
Owners:
• Metrological,• Geodetic, • Geologic and• Geophysical
institutions
Complemented by other instrument types: e.g. JILA-G, A10, IMGC, GABL, Sakuma, Faller, etc. and the new atom interferometers
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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
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The GGOS Idea
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
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.)
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Bad Homburg BHWettzell WEMedicina MC
Gravimetric residuals after combining AG and SGfor the sites Bad Homburg (D), Wettzell (D), Medicina (It)
Gravity variations at selected reference sites
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Example for strong gravity variations at the geodetic reference station Concepcion (Chile)
Gravity variations at selected reference sites
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TIGO Concepción (Chile), combined gravity residuals of SG-38 and FG5-227
(corrected for SG-drift, tides, air pressure and polar motion)
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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
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Which data are presently available?
Most of the observations are related to cooperation with other national institutions.
Source: S. Kenyon
National Geospatial Intelligence Agency (NGA), USA)
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Observations period1993 - 2006
Observations with FG5 and A10 absolute gravimeters
Example of absolute gravity networksFederal Agency for Cartography and Geodesy (BKG), Germany
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Gravity reference networks in specific regions
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, ...
Example: Absolute Gravimetry in AntarcticaSource: Amalvict et al., 2006
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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 BKGhttp://bgi.dtp.obs-mip.fr/ http://agrav.bkg.bund.de/
Standardised data upload with “project files”
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AG Database - AGrav
Implementation and test phase of the database complete
At present 26 instruments 419 AG stations 1339 AG observations
http://bgi.dtp.obs-mip.fr/ http://agrav.bkg.bund.de/
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Global Geodynamics Project (GGP)Global Network
Network of Superconducting gravimeters Absolute Gravity Sites in Agrav Database
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Realisation of a global gravity referencesystem
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”
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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!
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Thank you for the attention!