The Federal Office of Topography swisstopo is responsible for the maintenance of the coordinate reference frames in Switzerland. Beside the static reference frames, used for national surveying, the development of a kinematic model, mainly used for scientific investigations, is under development since many years. For the determination of vertical movements the analysis of more than 100 years of levelling observations showed a significant alpine uplift of maximally 1.5 mm/year relative to an arbitrarily chosen bench mark in Aarburg (at the south of the Jura mountains). For the determination of horizontal movements the various GPS-campaigns, measured since 1988, are the basis. With the Automated GNSS Network of Switzerland (AGNES), which operates permanently since 1998, valuable information can be extracted for 30 sites. The paper shows that the time series of AGNES nowadays allow statements concerning possible vertical movements. The potential of additional information sources, such as local tie surveys, are discussed. Comparisons of the results of the two independent measuring techniques GNSS and levelling are the main topic of the paper.

The official height system of Switzerland LN02 is based on levelling measurements only, without taking into account the gravity field. This causes inconsistencies for the surveyors who nowadays often determine heights out of GPS measurements and geoid information.A first step to overcome this problem is to introduce orthometric heights (LHN95) as the official national height system. This height system takes into account vertical movements and is based on a rigorous adjustment of all 1st and 2nd order levelling measurements since 1902. The necessary mean gravity values along the plumbline are calculated out of a 25 meter DHM and associated density models. Besides of orthometric heights also normal heights are calculated. This allows us to compare the Swiss heights with the heights of our neighbouring countries and with the European height system. Furthermore it is a necessary prerequisite for the transformation between national height systems and the unification of national vertical datums.With the introduction of a new vertical system we have to provide a transformation method from LN02 to LHN95. Our first approach for this transformation was to split the differences between a levelled and an orthometric system into several separate effects such as network distortions, vertical movements and the influence of the gravity field. These individual effects should be easier to interpolate than the differences as a whole.But even with the new orthometric height system full consistency between levelling and GPS measurements is not reached yet. We see systematic discrepancies between levelling, GPS and the geoid for which we have no explanation yet. The three data sets should be determined in one common adjustment process. This is not rigorously possible because, in general, the full variance-covariance information of all measurements is not available. In this paper a first approach and first results of a combined adjustment of GPS levelling and geoid are shown.

The existing old height system of Switzerland (LNO2) consists of purely levelled heights without considering gravity measurements. This causes difficulties in the application of modern techniques such as GPS for height determination in mountainous areas and in the data exchange with neighbouring countries. Therefore, a new rigorous height system LHN95, based on geopotential numbers and the corresponding geoid, is being determined at the Federal Office of Topography. LHN95 is treated as a kinematic network with respect to the Alpine uplift which reaches amounts of up to 1.5 mm/year [Gubler et al., 1981]. The corresponding relative vertical movements are determined by repeated observations of the first and second order levelling lines. For LHN95 it was decided to use orthometric heights as the official height system. This implies the use of the geoid as the reference surface. Because it has a smooth surface and can be interpolated easily even in mountainous areas, we consider it more convenient than the quasigeoid.

Since the last report in 2001 the old national levelling net- work block of Switzerland consisting of only 13 measur- ements was replaced by a current network of 380 observa- tions and more than 200 nodal points. Some problems arisen with the connections to the neighbour- ing countries because of crustal movements in the areas of border connections respectively instable benchmarks.