Establishment of a Global Absolute Gravity Network

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

https://www1.nga.mil/�

http://www.vniim.ru/�

2TG-SMM-2010 – St. Petersburg, Russia28.06.2010

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


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”


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


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


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.)

http://www.iag-ggos.org/about_ggos.php�


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Jan 2002 Jan 2003 Jan 2004 Jan 2005 Jan 2006 Jan 2007

Zeit

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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


Example for strong gravity variations at the geodetic reference station Concepcion (Chile)

Gravity variations at selected reference sites

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g -9

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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)


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


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)


Observations period1993 - 2006

Observations with FG5 and A10 absolute gravimeters

Example of absolute gravity networksFederal Agency for Cartography and Geodesy (BKG), Germany


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


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”


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/


Global Geodynamics Project (GGP)Global Network

Network of Superconducting gravimeters Absolute Gravity Sites in Agrav Database


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”


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!


Thank you for the attention!

Establishment of a Global Absolute Gravity Network

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