The IGFS Services and Centres are the “operating arms” of IGFS. The Centres are committed to produce services and products related to the gravity field of the Earth and/or the planets. The Centres within IGFS are approved by the IAG EC. Centres can include bodies of structures external to the IAG (e.g., the BGI which is reporting to FAGS). The Centres will have their own governing bodies, nominated according to internal rules, also taking into account the interests of the supporting entities. In particular, each governing body will have a Director, elected according to internal rules.

Centres will maintain a list of data and products, providing them to the general public according to their policy of dissemination; they will deliver services in the form of data archiving, data analysis, dissemation, software, training, initiation of measurement and data compilation campaigns etc. The activities of each Centre will be reviewed annually by the IAG-EC.

The IGFS coordinates the following “Level-1” IAG services and service centres:

• IHRF CC (International Height Reference Frame Coordination Center), Thessaloniki, Greece
  The IHRF CC coordinates the activities of the IHRF Reference Network Coordination, the IHRF Conventions’ Coordination, the IHRF Associate Analysis Centres, and the IHRF Combination Coordination. The IHRF CC has the responsibility to deliver the IHRF coordinates (𝑋, 𝑌, 𝑍, 𝐶) of the IHRF reference stations and a catalogue of the vertical datum parameters, i.e., the transformation parameters between the existing local height systems and the IHRF.

• BGI (Bureau Gravimetrique International), Toulouse, France
  The overall task of BGI is to collect, on a world-wide basis, all measurements and pertinent information about the Earth gravity field, to compile them and store them in a computerized data base in order to redistribute them on request to a large variety of users for scientific purposes.

• ISG (International Service for the Geoid), Milano, Italy
  The main tasks of ISG are to collect geoid data on a worldwide scale, to collect and distribute software for geoid determination, to conduct research on procedure for geoid determination, to organize Geoid schools, and to edit and distribute the Newton’s Bulletin.

• ICGEM (International Center for Global Earth Models), Potsdam, Germany
  The main tasks of ICGEM are to collect and archive all existing global gravity field models, web interface for getting access to global gravity field models, web based visualization of the gravity field models their differences and their time variation, web based service for calculating different functionals of the gravity field models, web site for tutorials on spherical harmonics and the theory of the calculation service.

• COST-G (International Center for Global Earth Models), Bern, Switzerland

  The International Combination Service for Time-variable Gravity Fields (COST-G) is the Product Center of the International Gravity Field Service (IGFS) for time-variable gravity fields. COST-G provides consolidated monthly global gravity models in terms of spherical harmonic (SH) coefficients and thereof derived grids by combining solutions from individual analysis centers (ACs). The ACs adopt different analysis methods but apply agreed-upon consistent processing standards to deliver time-variable gravity field models, e.g. from GRACE/GRACE-FO low-low satellite-to-satellite tracking (ll-SST), high-low satellite-to-satellite tracking (hl-SST), Satellite Laser Ranging (SLR).

• IDEMS (International Digital Elevation Model Service), ESRI, Los Angeles, USA
  The main tasks of IDEMS are the distribution of data and information about Digital Elevation Models, relevant software and related datasets (including representation of Inland Water within Digital Elevation Models) which are available in the public domain.

• IGETS (International Geodynamics and Earth Tide Service), Strasbourg, France
  The primary objective of IGETS is to provide a Service to monitor temporal variations of the Earth gravity field through long-term records from ground gravimeters, tiltmeters, strainmeters and other geodynamic sensors. GETS continues the activities of the GGP to provide support to geodetic and geophysical research activities those of ICET in collecting, archiving and distributing Earth tide records.

• IGFS-TSC (Technical Support Centre of IGFS), NGA Saint Louis, USA
  The IGFS Technical Centre, located at the National Geospatial-Intelligence Agency, USA, will play a special role in advice on global models, geoid and gravity, especially related to the global ultra-high resolution geopotential models (EGM2008 and successors).