As the quality of space geodetic positioning results continues to
improve, our ability to detect small deviations from linear motion
increases. Large-scale, regional, and local loading effects can
contribute to such motions and space geodesy is proving useful to
monitor such processes. But technique errors and other effects
can also contribute to apparent non-linear motions, complicating
the interpretation of geodetic time series. Analysis of GNSS time
series is particularly difficult in many cases due to frequent
equipment changes, not all of which are well documented.

Handling these and other types of non-linear motions optimally in
forming long-term reference frames, such as the International
Terrestrial Reference Frame, is challenging. Various approaches
have been proposed and discussed. Experiences with the recent
ITRF2008 combination provide an opportunity to reconsider some of
the issues involved using consistent, reprocessed time series that
incorporate new analysis models and updated processing strategies.
It is important to examine, among other things, how different
approaches to handle non-linear motions affect the ITRF datum
(origin, scale, and orientation).

Papers are sought that study all aspects of these issues, including
multi-techique combination methods, characterization and treatment
of various systematic errors, datum specification, and future
directions. Automated algorithms to detect discontinuities in
position and velocity time series are particularly requested, as
this has become a major complication in realizing GNSS reference
frames. Any other reference frame-related issues specific to the
individual observing techniques are also of interest to this session.