Terms of Reference

Terms of Reference


The International Gravimetric Bureau (BGI) is the scientific service of IAG aimed at ensuring the data inventory and the long term availability of the gravity measurements acquired at the Earth’s surface. Its main task is the collection, validation and archiving of all kind of gravity measurements (relative or absolute) acquired from land, marine or airborne surveys and the diffusion of the derived data and products to a large variety of users for scientific purposes.

Created in 1951, BGI has played a major role before the era of the satellite gravity missions (CHAMP, GRACE, GRACE Follow-on and GOCE) for supporting the computation of regional or global models of the Earth’s gravity field, primarily based on terrestrial gravity measurements together with Satellite Laser Ranging (SLR) data. It has also provided the accessibility to the global network of stations for referencing the worldwide gravity data surveys in a same absolute reference system (Potsdam and IGSN71 networks). Today, terrestrial gravity data, derived from both field (ground, airborne and seaborne surveys) and laboratory measurements, remain fundamental for the calibration/validation of the results derived from the satellite gravity missions and for providing the high-resolution components of the Earth’s gravity field, not accessible from the satellite observations.

The increasing facilities in the relative or absolute gravity measurements and the developments of new sensors (including cold-atoms technologies) facilitate homogeneous and accurate worldwide observations of the Earth’s gravity field and the determination of its variations in space and time. The BGI activities are coordinated with those of other IAG gravity services (ISG, IGETS, ICGEM, IDEMS) through the International Gravity Field Service (IGFS).


The primary task of BGI is to improve the global knowledge of the Earth’s gravity field through the collection, homogenization and validation of all available gravity measurements (relative or absolute) and make this information available to a large variety of users for scientific applications. With this aim, BGI holds and maintains the 4 fundamental global databases of relative and absolute static gravity measurements and develops services and products to serve the scientific community. The most current services provided by BGI include:

  • Access of gravity data, reference stations, products, software and documentation
  • Archiving and validation of gravity dataset and products provided to BGI and attribution to data providers of a traceable international reference through a Digital Object Identifier (DOI)
  • Realization and/or evaluation of global models (e.g. World Gravity Map, Earth Geopotential Models) as well as regional data compilations carried out for gravity or geoid studies

BGI also actively contributes to the definition of protocols, practices and recommendations aimed at improving the gravity data acquisition and processing and the realization of gravity surveys and networks. BGI is more specifically involved in the following actions:

  • Definition and establishment of the “International Gravity Reference System & Frame” IAG JWG 2.1.1.
  • Evaluation of new sensors (cold-atom absolute gravity meters).
  • Support to the realization of national absolute gravity networks.

Finally, BGI also contributes with his collaborators to other research and development activities (software developments, research in geophysics and geodesy, etc.), to educational activities in gravimetry (summer schools, tutorials, etc.).

Central Bureau & contributors

BGI has its central bureau in Toulouse, France (GET/OMP) and operates with the support of various French agencies (CNES, CNRS/INSU, IGN, IRD, SHOM, BRGM, IFREMER) and Universities (Toulouse, Paris, Strasbourg, Montpellier, Brest, Le Mans). BGI services also benefits from the close collaboration of other agencies from Germany (BKG), Italy (POLIMI), Greece (AUTH), Czech Republic (VÜGTK), Denmark (DTU) and USA (NGA). The contribution of national institutions in charge of the gravity data acquisition is also essential for ensuring a long term usability and sustainability of the highest-quality of gravity data provided by BGI.

IAG Terms of References

Terms of Reference of BGI are described in the IAG Geodesist’s Handbook 2020 (Journal of Geodesy, vol 94, N°11)

Previous versions :

Link to IAG Office webpage : http://www.iag-aig.org

Link to IAG/GGOS Services : https://ggos.org/services/

Link to IAG/GGOS main page : https://ggos.org/

How to provide data to BGI ?

As a service of IAG and FAGS, the final task of BGI is to give access to the largest scientific community to relative and absolute measurements of the Earth gravity field and related information. The permanent archiving of new incoming gravity data sets is crucial to improve the coverage and accuracy of the global gravity database and to improve our knowledge of the Earth gravity field. It also enables BGI to validate the gravity observations in a global reference frame and restore them in standard and unified formats useful for various users.

BGI currently collect & provides information on:

  • Earth gravity measurements (relative & absolute measurements ; land, marine & airborne data)
  • Gravity base reference stations
  • Other gravimetry-related information (bibliography, software…)

The contribution of agencies and institutions involved in relative or absolute gravity data acquisition is welcome to ensure the best service to community.

Contributors interested in archiving their gravity observations as public or proprietary data are invited to contact BGI or to upload data files directly from the BGI website. All kinds of gravity data (from land, marine, or airborne surveys as well as from absolute measurements) can be sent to BGI, with or without restrictions of redistribution to be specified by the contributors. ASCII data files containing all necessary information and quantities are preferred (station coordinates, gravity measurements and accuracies; gravity corrections; reference geographic, height and gravity systems, etc.).