KONINKLIJKE ACADEMIE VOOR OVERZEESE WETENSCHAPPEN ...

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GPS observations can be interpreted in different ways. We have considered
the baseline vector (fig. 5) between two adjacent points as the principal GPS
observation.
The baseline vectors were computed using the BERNESE software [4], The
BERNESE software is a well-known scientific software developed at the
University of Bern. The components (AX, AY, AZ) of the baseline vectors were
later used for the computation of the Cartesian coordinates (X, Y, Z) of each
point. For the least squares adjustment of all observations, the MOVE3 software
[5] was used. This software, developed at the Delft Technical University, has the
great advantage that it not only computes the accuracy of the coordinates but also
the reliability of the observations. Using some statistical testing, outliers in the
observations can be detected and removed.
The Linking-up with ITRF
The ITRF [6] (fig. 6) consists of a large number of stations, globally spread
and equipped with various types of satellite tracking tools. For our purposes, the
GPS data were the most important.
On a voluntary basis, all these stations send their observations to the IGS
(International GNSS Service), where not only the global coordinates (X, Y, Z) of
each point are computed but their velocities (VX, VY, VZ) too. The mean period of
our observations was 2005.4. The global coordinates computed by the IGS [7]