Paul Rebischung, Université de Paris, Institut de physique du globe de Paris, CNRS, IGN, F-75005 Paris, France; ENSG-Géomatique, IGN, F-77455 Marne-la-Vallée, France, Arturo Villiger, University of Bern, Astronomical Institute, Bern, Switzerland, Thomas Herring, Massachusetts Institute of Technology, Department of Earth, Atmospheric and Planetary Sciences, Cambridge, MA, United States and Michael Moore, Geoscience Australia, Canberra, ACT, Australia