The Working Group on 'Integration of dense velocity fields into the ITRF' (2011-2015) is part of the International Association of Geodesy (IAG) Sub-Commission 1.3 'Regional Reference Frames' which is imbedded in the Commission 1 on Reference Frames. It is the follow up of the Working Group on 'Regional Dense Velocity Fields' which was part of IAG Sub-Commission 1.3 'Regional Reference Frames' from 2007 until 2011.
Most of the different IAG Regional Reference Frame Sub-Commissions (for Europe (EUREF), South and Central America (SIRGAS), North America (NAREF), Africa (AFREF), Asia & Pacific (APREF), and Antarctica (SCAR)) within IAG sub-commission 1.3 on "Regional Reference Frames" have been using GNSS for computing a regional densification of the global ITRF (International Terrestrial Reference Frame) for their continent. Up to now, no comparisons were done between these different regional solutions and no attempt has been made to merge them into once consistent ITRF densification network.
With the aim to provide a globally referenced dense velocity field based on GNSS observations, the WG "Integration of dense velocity fields into the ITRF" has invited all regional reference frame sub-commissions to submit SINEX solutions for the dense GNSS networks covering their continent to the WG. In addition, these sub-commissions are playing an important role in our Working Group as they have the necessary knowledge to clarify any problems or inconsistencies that might arise with GNSS stations in their region. As such, there is a direct communication line between the final combination of the solutions and the regional information.
In order to provide a global velocity field, the WG combines first the solutions provided by the sub-commission on a weekly level and then stacks the weekly combined solutions to obtain a consistent densification of the ITRF. It will be the first time that these "regional" densification solutions will be inter-compared and to succeed, the WG is putting special emphasis on the consistency of different data analysis strategies, and especially on the meta-data used. This is done in collaboration with the IERS and the IGS Terrestrial Frame Combination Center.
A preliminary combination of the regional densification solutions in order to derive a cumulative position and velocity solution for 1770 stations as well as their associated residual position time series has been done and presented at the IAG Symposium in Postdam in September 2013. We will update soon this combination by adding ~1000 stations and improving the consistency of the discontinuities. The main drawback is a mix of antenna calibration models.
For this reason, all contributors will submit new weekly solutions compliant with IGS repro2 in 2014. A new final combination will be done in 2014.