Position variations in trf frame The International Terrestrial Reference Frame(ITRF defines the positions and velocities of -1000 locations around the world(GPs, VLBl, slr and dOris Frame is defined to have no net rotation when motions averaged over all tectonic plates However, a location on the surface of the earth does not stay at fixed location in this frame: main deviations are: Tectonic motions(secular and non-secular) Tidal effects(solid earth and ocean loading Loading from atmosphere and hydrology First are normally accounted for 04/17/02 12.540Lec1804/17/02 12.540 Lec 18 8 Position variations in ITRF frame • The International Terrestrial Reference Frame (ITRF) defines the positions and velocities of ~1000 locations around the world (GPS, VLBI, SLR and DORIS). • Frame is defined to have no net rotation when motions averaged over all tectonic plates. • However, a location on the surface of the Earth does not stay at fixed location in this frame: main deviations are: – Tectonic motions (secular and non-secular) – Tidal effects (solid Earth and ocean loading) – Loading from atmosphere and hydrology • First are normally accounted for