The combined adjustment of GPS/Levelling observations on benchmarks with
gravimetric geoid heights has been the focus of extensive research both from the
theoretical and practical point of view. Up until today, with few exceptions, the
main blame for the inconsistencies/disagreement between these three types of
heights has been put to the geoid heights due mainly to their poorer accuracy.
With the advent of the new CHAMP- and GRACE-based global geopotential
models and the realization of EGM2008 the achievable cumulative geoid accuracy
has improved significantly so that its differences to GPS/Levelling heights
reach the few cm level. In Greece, GPS observations on BMs are very scarce and
cover only small parts, in terms of spatial scale, of the country. Recently, an effort
has been carried out to perform new GPS measurements on levelling BMs, so that
reliable GPS/Levelling and gravimetric geoid height adjustment studies can be
carried out. This resulted in part of North-Western Greece to be covered with
reliable observations within an area extending 3 in longitude and 1 in latitude.
Therefore, some new potential for the common adjustment of the available
geometric, orthometric and geoid heights, using various parametric surfaces to
model and interpret their differences, are offered. These are used to come to some
conclusions on the accuracy of the various geoid models used (both global
geopotential and local gravimetric models), while an extensive outlook is paid
to the questionable behaviour of the orthometric heights. The latter is especially
important for the Greek territory since the available benchmarks are delaminated
in so-called “map-leaflets” and a common adjustment of the entire vertical
network has not been carried out so far. It is concluded that even between
neighbouring “map-leaflets” large biases in the adjusted GPS/Levelling and
gravimetric geoid heights exist, which indicates distortions in the Greek vertical
datum as this is realized by the levelling benchmarks. Given that the latter are
commonly used for everyday surveying purposes, conclusions and proposals on
the determination of adjusted orthometric heights are finally drawn.