Toward a dense italian GPS velocity field: data analysis strategies and quality assessment

A test combination procedure of loose constrained SINEX solutions has been
set up with the aim to integrate different network solutions (clusters of GPS
site coordinates) processed by different analysis groups. Two solution types have
been combined on a daily basis, one cluster of about 60 sites processed with
the Bernese software and a second cluster of about 30 sites processed with the
Gamit software. The chosen networks consists in 15 overlapping EUREF sites on
which the combination test is figured out. In origin each solution is obtained in
a loose constrained reference frame and archived in SINEX format, the full time
series span a period of 2.5 years. If the reference frame constraints, if present, are
conveniently relaxed in the original solutions, the combination of daily solutions
can be carried out without the removal of relative rotations between reference
frames and the different contributing SINEX solutions may be merged (in a least
squares sense) into a combined consensus solution. The corresponding velocity
fields, computed for the common sites, are consistent with respect to each other
and the combined time series show a repeatability of a few millimeters in the
vertical and 1–2 millimeters in the horizontal components respectively.