TRF Datum Definition and Geocenter Motion Estimate

Are satellite geodesy techniques currently able to accurately measure the geocenter motion? We try to discuss this question using the geometric method based on the three translation components of the 7 Helmert transformation parameters under minimum constraints condition. Geocenter motion estimates as results from independent combinations of time series of station postions available in weekly sinex files from SLR, GPS and DORIS techniques will be compared. Expecting a few millimeter variations, care should be paid to the analysis strategy used for geocenter motion estimates, being intimately dependent on the datum definition of the underlying Terrestrial Reference Frame (TRF). The most challenging task is then to be able to de-correlate geocenter motion signal from other computational artefact, being often inherent to the TRF implementation. We concentrate mostly on seasonal variations, more easily detectable by satellite geodesy than the secular part believed to be slow over a time period larger than the available data span. Some conclusions will be drawn and implications for IERS, in particular the next ITRF solution and the Global Geophysical Fluids Product Center, will be addressed.