Some Thoughts on Establishment and Maintenance of Terrestrial Reference Frame Considering Non-linear Variation

Because of the mass redistribution of the geophysical fluid loading,obvious non-linear variation exists in most of the global GPS sites(mainly seasonal variations of the vertical component).And its transient motion with respect to the reference frame can not be completely described by a linear velocity.We consider and deal with the non-linear and seasonal variation characteristics of frame sites appropriately,together with combination of the linear velocity model are of great importance in the establishment and maintenance of the dynamic terrestrial reference frame.Firstly,the current status of the global and regional reference frames have been briefly introduced.Then,the disadvantages of the linear ITRF model has been investigated,leading to the thoughts of building velocity model considering different types of non-linear variation,so as to establish and maintain a dynamical reference frame.Based on this,method of regional reference frame establishment and maitenance has been discussed.Finally,we look into the future developments of ITRF under the GGOS background.