Accuracy Assessment of the ITRF Datum Definition

One of the main objectives of the International Terrestrial Reference Frame (ITRF) is to provide a standard global reference frame having the most attainable accuracy of its datum definition in terms of its origin, scale and the time evolution of its orientation. This latter should satisfy, by convention, the no net rotation condition. The accuracy of the ITRF datum specifications are obviously dependent on the quality and the internal consistency of the solutions contributing to its elaboration and definition. In this paper, we examine and review the quality of the current ITRF datum definition with an accuracy assessment based on the ITRF2005 results and by consistency evaluation with respect to ITRF2000. The availability of time series of station positions and Earth Orientation Parameters, used now as input for the current ITRF construction, will facilitate the accuracy assessment. When rigorously stacking the time series of a given technique to estimate a long-term frame solution, the 7 transformation parameters of each individual temporal set of station positions are also estimated. By applying dynamically internal constraints (equivalent to minimum constraints approach) over the time series of the 7 parameters, we then preserve some physical “natural” parameters as for instance the scale and the origin from VLBI and SLR, respectively. Our conservative evaluation of the estimated accuracy of the ITRF datum definition is that the origin and its rate are accurate at the level of 5 mm and 2 mm/yr, the scale and its rate are at the level of 1 part per billion (ppb) and 0.1 ppb/yr and the No-Net-Rotation condition implementation is at the level of 2 mm/yr.