International Association of Geodesy (IAG)


Associate Member since 2006
Official Website (external link):


The International Association of Geodesy (IAG) is the scientific organisation responsible for the field of Geodesy. It has been a member association of the International Union of Geodesy & Geophysics (IUGG) since the inception of the IUGG in 1919. In 1862 the "Mitteleuropäische Gradmessung" - predecessor of the IAG - was established. The work of the IAG is performed within a component structure consisting of: commissions, inter-commission committees, services, the Communication & Outreach Branch, and the Global Geodetic Observing System (GGOS). The GNSS-related IAG service is the International GNSS Service (IGS), the reference frame IAG service is the International Earth Rotation & Reference System Service (IERS), and the time reference IAG service is the Time Department of the Bureau of Weights & Measures (BIPM).
The classical definition of Geodesy is the science concerned with the shape, size, and the gravity field of the Earth. Geodesy today is much more than that. It is a geoscience that nowadays deals with:
  • the monitoring of the solid Earth (displacement, subsidence or deformation of the ground and structures, due to tectonic, volcanic and other natural phenomena, as well as human activity);
  • the monitoring of variations in the liquid Earth (sea level rise, ice sheets, mesoscale surface topography features, ass transport);
  • monitoring variations in the Earth's rotation (polar motion, the length of the day);
  • monitoring the atmosphere with satellite geodetic techniques (ionosphere and troposphere composition and physical state);
  • monitoring the temporal variations in the gravity field of the Earth;
  • determining satellite orbits (including earth observation and navigation satellites);
  • determining positions, and their changes with time, of points on or above the surface of the Earth with the utmost accuracy.
Due to today's significantly improved geodetic instrumentation and techniques, Geodesy is more concerned with changes in the "geometry" and "gravimetry" than in the past, of features on, beneath or above the surface of the solid Earth and oceans. In the past, the main "customers" of Geodesy came from the surveying, mapping and geospatial disciplines, while today Geodesy serves all geosciences, including the geophysical, oceanographic, atmospheric, hydrological and environmental science communities. Geodetic "products" are not only contributing to our understanding of the Earth, they are also fundamental for many societal benefit areas, ranging from disaster prevention and mitigation, to the protection of the biosphere and the environment. Geodesy, in so many ways, contributes to increased security, to a better use of natural resources, and in general to satisfying the goal of sustainable development on our fragile planet.
Of particular note is that Geodesy serves society by providing reference frames for a wide range of practical applications, such as navigation on land, sea and in the air, and from construction of infrastructure to the determination of reliable boundaries of real estate properties and maritime zones. In the past these reference frames were created on a national or regional level. Today, through the exploitation of the existing and planned Global Navigation Satellite Systems such as GPS, GLONASS, Galileo, BeiDou, Geodesy provides access to point coordinates in a global reference frame anytime and anywhere on the Earth's surface with centimetre-level accuracy.

IAG's role and the value gained in the ICG

The IAG, through its services IGS, IERS and BIPM (Time Department) specifically dealing with geodetic and time reference frames, and precise positioning using GNSS, is an ICG Associate Member with a unique and highly valued set of expertise. The IAG is a co-chair of ICG Working Group D "Reference Frames, Timing and Applications", and has been working with its sister organisation the FIG, to promote the use of a single International Terrestrial Reference Frame (ITRF) for the precise alignment of individual GNSS datums, and to document these geodetic and time reference frames. In addition, the IAG and IGS are the precise GNSS positioning experts, responsible for the development of a range of GNSS techniques, data products and services to support the high precision GNSS user. In particular, the IGS has operated a globally distributed network of several hundred ground GNSS tracking stations since 1994. Initially the International GPS Service (as it was then known) generated a series of GPS data products (principally raw tracking data, and computed satellite orbit and satellite clock error states). Over a decade ago this was expanded to include GLONASS tracking and products, and most recently (since 2012) the IGS has been running a multi-GNSS test experiment known as M-GEX. The IAG and IGS are cooperating with Working Group A to define the scope and nature of an International GNSS Monitoring and Assessment (IGMA) activity. It is envisaged that the IAG/IGS would provide some components of a future IGMA service.
The ICG has considerable visibility within the IAG, with the IAG president (and in his place the vice-president) attending many of the annual ICG meetings. The primary focus is the ITRF and the contribution of the IGS to multi-constellation GNSS performance monitoring.

Presentations made in the ICG annual meetings

Year Title and Speaker (link to the presentaion material)
2013 (ICG-8) Thoughts on GNSS System Times and Broadcast Time Scales - Felicitas ARIAS and Wlodek LEWANDOWSKI
2013 (ICG-8) Progress on Works Related to the Proposed Redefinition of UTC - Felicitas ARIAS and Wlodek LEWANDOWSKI
2013 (ICG-8) Rapid UTC: A Step Forward for Enhancing GNSS System Times - Felicitas ARIAS
2013 (ICG-8) Update on the International Terrestrial Reference Frame (ITRF) - Zuheir ALTAMIMI
2013 (ICG-8) Impact of a Possible Redefinition of Coordinated Universal Time on GNSS Interoperability - Wlodek LEWANDOWSKI
2012 (ICG-7) The IGS: a Multi-GNSS Service - Chris RIZOS
2012 (ICG-7) The Role and Importance of the ITRF for Sustainable Development - Zuheir ALTAMIMI
2012 (ICG-7) EUREF Infrastructure Galileo Ready - Johannes IHDE
2012 (ICG-7) Recent Developments in Time References - Wlodek LEWANDOWSKI
2012 (ICG-7) GNSS is the Core Technology to Support GGOS Applications - Chris RIZOS
2011 (ICG-6) Multi-GNSS within IAG/IGS - Chris RIZOS
2010 (ICG-5) Recent developments in the IGS - John DOW
2010 (ICG-5) Impact of multi-GNSS on international timekeeping - Felicitas ARIAS
2010 (ICG-5) Latest Developments with ITRF 2008 - Zuheir ALTAMIMI
2009 (ICG-4) BIPM Actions and Developments Related with GNSS - Wlodek LEWANDOWSKI
2009 (ICG-4) The International Terrestrial Reference System (ITRS) - Claude BOUCHER
2009 (ICG-4) Fundamentals on UTC - Relationship between GNSS Times - Felicitas ARIAS and Wlodek LEWANDOWSKI
2008 (ICG-3) International GNSS Service & ICG: Status Update - John DOW
2008 (ICG-3) IAG Components Supporting ICG Goals - Chris RIZOS
2008 (ICG-3) Satellite Laser Retroreflectors for GNSS satellites: ILRS International Standard - Michael PEARLMAN
2008 (ICG-3) Use of International References for GNSS operations and applications - Felicitas ARIAS and Wlodek LEWANDOWSKI
2008 (ICG-3) Development of the EUREF GNSS Services and Reference Networks - Johannes IHDE
2008 (ICG-3) SIRGAS: reference Frame for GNSS Applications in Latin America - Ruth NEILAN
2008 (ICG-3) The Africa Reference Frame Project - AFREF - Richard WONNACOTT
2007 (ICG-2) The Global Geodetic Observing System (GGOS) - Ruth NEILAN
2007 (ICG-2) Standardization of Geodetic Reference Frames for GNSS based on ITRF - John DOW
2006 (ICG-1) AFREF Activities and the IAG program: Global Geodetic Observing System (GGOS) - Ruth NEILAN
2006 (ICG-1) Recent developments in the IGS - John DOW

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