[G01-3] Reference frame methodology and implementation

[G01-3-04] Differential station coordinates changes (velocities) versus coordinate differences (epoch solutions) for realising the time dependence in ITRF

^○Hermann Drewes (Technical University Munich, Munich, Germany)

The International Terrestrial Reference Frame (ITRF) and its continental densifications (e.g. EUREF, SIRGAS) provide differential coordinate changes (linear coordinate derivatives, i.e. constant velocities) for interpolating or extrapolating the reference station coordinates to an arbitrary epoch, e.g. for satellite tracking or precise terrestrial positioning. These station velocities are also applied for geographical interpolation of the movements of intermediate points, e.g. used in engineering, surveying, precise navigation, and geodynamic studies. If the velocities are not constant, e.g. due to effects caused by seismic events or environmental non-linear surface deformations, the interpolation or extrapolation between epochs has to be done piecewise for all contemplable periods and effects, and the geographical interpolation has to follow the same procedure which may be very complicated in unstable regions. The present paper describes an option to use frequent (e.g. monthly) epoch reference coordinates instead of velocities, and to use them for practical applications (e.g. geographical interpolation of time-dependent coordinates of other points of the Earth surface). The advantage is that the reference stations' epoch coordinates include all occurred changes between the epochs, i.e. linear and non-linear station movements, and discontinuities caused by seismic events or changes of the reference frame. The method is tested in global, continental and national networks and yields good results.