Analysis and refined computations of the international terrestrial reference frame

The International Terrestrial Reference Frame (ITRF) is realized by epoch positions and linear velocities of a set of geodetic points on the Earth's surface. Up to the present, i.e. the ITRF2000, the computation is done by a 14 parameter similarity transformation (7 for the stationary and 7 for the kinematic coordinates) of individual solutions from the different space geodetic observations (VLBI, SLR, GPS, DORIS) and the simultaneous adjustment of the position and velocity coordinates. The analysis of the ITRF2000 shows some problems resulting from this transformation procedure. The refined TRF computations done by DGFI use unconstrained normal equations from the solutions of the individual techniques. After a thorough analysis and editing they are combined in a first step internally by accumulation per technique. In the second step the normal equations of the unique techniques are accumulated for an inter-technique combination. The datum of the final TRF solution is attained by no net rotation w.r.t. ITRF2000. Detailed comparisons show a generally good agreement between the DGFI TRF and the ITRF2000. Some outliers are discussed.