Terrestrial Reference Frames: The Fundament for Geodetic Earth Observation and all Positioning Applications

Global reference systems and their implementations such as the International Terrestrial Reference Frame (ITRF) provide the foundation for determining positions on Earth and in space as well as for reliably quantifying our planet’s changes due to geodynamic processes and ongoing climate change. The ITRF ensures a uniform basis for all positioning and satellite navigation applications, and thus plays an elementary role in our modern society. The ITRF is the standard reference recommended by a number of international scientific organizations, including the International Union of Geodesy and Geophysics (IUGG) and the International Association of Geodesy (IAG) for positioning, satellite navigation and Earth science applications, as well as for the definition and alignment of national and regional reference frames. In 2015, the United Nations adopted the resolution “Global Geodetic Reference Frame for Sustainable Development”, which clearly expresses the importance of a global geodetic reference frame for society, economy and science. Four geodetic space techniques are currently used for the ITRF computation: Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS). The current realization of the International Terrestrial Reference System (ITRS), the ITRF2020, comprises 3D coordinates and velocities of around 1900 globally distributed observing stations.