Geodesy

Definition

The classical definition of geodesy [pronunciation: jee-od-uh-see] is that it is the science concerned with the shape, size, and the gravity field of the Earth. However, geodesy today is much more than that. Nowadays, it is a geoscience that deals with:

• monitoring 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);

• monitoring variations in the liquid Earth (sea-level rise, ice sheets, mesoscale surface topography features, mass 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 Earth's gravity field;

• 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.

Reference frames

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, the building of infrastructure and the determination of reliable boundaries for real estate properties or even maritime zones. In the past, such reference frames were created on a national or regional level. Today, through the exploitation of the existing and planned Global Navigation Satellite Systems (GNSS) such as GPS, Glonass, Galileo and Compass/BeiDou, geodesy provides access to point coordinates in a global reference frame anytime and anywhere on the Earth's surface with centimetre-level accuracy.

Due to today's significantly improved geodetic instrumentation and techniques, geodesy has become more concerned with changes in the ‘geometry' and ‘gravimetry' of features on, beneath or above the surface of the solid Earth and oceans than it was previously. What are the implications of this development for geodesy's role? In the past, geodesy's main ‘customers' came from the surveying, mapping and geospatial disciplines, whereas 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, but they also benefit many societal activities, ranging from disaster prevention and mitigation to the protection of the biosphere and the environment. Geodesy contributes in countless ways to increased security, a better use of natural resources and, ultimately, to achieving the goal of sustainable development on our fragile planet.

The International Association of Geodesy

The International Association of Geodesy (IAG) is the scientific organisation responsible for the field of geodesy. It is a member association of the International Union of Geodesy & Geophysics. Since the predecessor of the IAG, the ‘Mitteleuropäische Gradmessung', was established back in 1862, IAG is celebrating its 150^th anniversary in 2012. 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.

The new IAG Executive Committee was established in July 2011 at the conclusion of the IUGG's General Assembly in Melbourne, Australia. At its most recent meeting on 5^th December 2011, the IAG's new commission structure was finalised. Outcomes of that EC meeting will be featured in the next report to GIM International readers.

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