IC SG9

Future developments of ITRF models and their geophysical interpretation

Chair: A. Dermanis (Greece)
Affiliation:Comm. 1 and IERS

Terms of Reference

The realization of a reference system by means of a refer-ence frame, in the form of coordinate time series or coor-dinate functions for a global set of control stations is a complicated procedure. It involves input data from various space techniques each one based on its own advanced modelling and observation analysis techniques, as well as, criteria for the optimal selection of the time evolution of the reference frame among all data compatible possibili-ties. The relevant “observed” coordinate time series demon-strate significant signals of periodic, non-periodic varia-tions and discontinuities, which pose the challenge of departing from the current ITRF model of linear time evo-lution, realized by reference epoch coordinates and con-stant velocities.

The remaining residual signal in coordinate variations is dominated by an almost periodic term with varying amplitude and phase, especially in the height component. The inclusion of additional terms in the ITRF model is an intricate problem that deserves further research and careful planning. It is also important to understand the nature of these coor-dinate variations in order to adopt models that are mean-ingful from the geophysical point of view and not a simple fit to the observed data. Since geophysical processes causing coordinate variations also cause variations in the gravity field, it is worthwhile to investigate the possibility of incorporating result results from space gravity missions in ITRF modelling. The working group is primarily aiming in identification of new ITRF models, investigation of their performance and motivation of relevant scientific research.

Objectives

• Geophysical interpretation of non-linear coordinate variations and sevelopement of relevant models
• Extension of ITRF beyond the current linear (constant velocity) model, treatment of periodic and discontinuous station coordinate time series and establishment of proper procedures for estimation of extended ITRF parameters and quality assessment of the obtained results.

Program of activities

• Launching of a web-page for dissemination of informa-tion, presentation, communication, outreach purposes, and providing a bibliography.
• Working meetings at international symposia and pre-sentation of research results in appropriate sessions.
• Organization of workshops dedicated mainly to problem identification and motivation of relevant scientific research.
• Organization of a second IAG School on Reference Frames.

Membership

A. Dermanis (Greece), chair
Z. Altamimi (France)
X. Collilieux (France)
H. Drewes (Germany)
F. Sansò (Italy)
T. van Dam (Luxembourg)