ITRF

The International Terrestrial Reference Frame (ITRF) is a geocentric, earth-fixed reference frame used to provide a globally consistent set of coordinates for points on or near the Earth's surface. It serves as the standard reference for geodesy, surveying, navigation, and Earth science, enabling precise tracking of positions, crustal motion, and geophysical signals over time.

ITRF is maintained by the International Earth Rotation and Reference Systems Service (IERS) and realized by combining observations from multiple space geodetic techniques. These include global navigation satellite systems (GNSS), very long baseline interferometry (VLBI), satellite laser ranging (SLR), and DORIS. A given realization yields station coordinates and velocities, a scale, and Earth orientation parameters (EOP). Realizations are published periodically (examples include ITRF2000, ITRF2008, ITRF2014, ITRF2018, and ITRF2020), each tied to a reference epoch and expressed with precise formal uncertainties.

The frame’s origin is the Earth's center of mass, and its axes are fixed to the terrestrial reference system with orientation tied to established celestial reference frames through the EOP network and IERS conventions. Each station contributes a stable position at the reference epoch and a velocity that describes its motion relative to the geocenter, reflecting plate tectonics and other vertical and horizontal movements. The ITRF also provides a stable global scale parameter.

Applications of the ITRF include precise satellite navigation, geophysical and geodetic research, crustal deformation studies, sea-level investigations, and climate science. As measurement techniques and models advance, new realizations of the ITRF are issued to improve accuracy and consistency across the geodetic community.