Analysing geodetic fixed point survey time series to evaluate the long-term activity of DSGSDs in Austria

A fixed point in geodesy is a stable survey point that fulfils the following two conditions: The point is known in coordinates from a previous survey (by position and/or height) and the point is permanently marketed (stabilised) in nature. Fixed points serve as reference points for surveys of all kinds. To determine the coordinates of the fixed points in the modern European reference system ETRS89, not only all previously measured GNSS vectors are used, but also all terrestrial observations measured since 1906, i.e. direction, elevation angle and distance measurements (Otter et al., 2017). More than 20.000 individual RTK measurements on these fixed points by using APOS (Austrian Positioning Service) complete the measurement dataset. Approximately 60.000 triangulation points (TPs) form a three-dimensional point network throughout Austria, whereas about 70 % of all TPs have multiple measurements. Fixed points should be stable, but this is not always the case, as fixed points are often influenced in their spatial position by gravitational mass movements, among other factors.

We have interpreted the entire elevation model/hill shade of Austria (1-metre resolution, based on ALS-data) and mapped all DSGSDs that manifest themselves geomorphologically in the terrain. This data set was intersected with the fixed points in order to identify those points that lie within a DSGSD. By analysing the results of the individual fixed point survey epochs, conclusions can be drawn about deformation rates of mass movements after excluding possible sources of error and statements can be made retrospectively up to the year in which the particular point was created (Otter et al., 2017).

Overall the fixed point measurements of the Federal Office of Metrology and Surveying Austria (BEV) represent a high quality and long term dataset that stands for its own and can support other slope monitoring methods. The interpretation of the dataset concerning slope deformations is not trivial but can deliver information of the range of movements over decades with uncertainties of 0 to 1.5 cm.

By combining different data sources (InSAR, ALS, in-situ measurements, fixed points, ...) we can present a preliminary, comprehensive data set on the activity status and often associated deformation rates of DSGSDs in Austria.

References:

Otter, J.; Imrek, E.; Melzner, S. (2017) Geodätische Grundlagenvermessung als Werkzeug in der Naturgefahrenanalyse in: Wimmer-Frey, I.; Römer, A.; Janda, C. [Hrsg.] Angewandte Geowissenschaften an der GBA. Wien, S. 147–152.