Report of the D-A-CH geoid and height unification project and prospects for the extension to the European Alps and beyond

The D-A-CH geoid project was initiated in 2017 between the national mapping agencies of Germany (BKG), Austria (BEV) and Switzerland (swisstopo), as well as the regional authorities of the German federal states of Bavaria (LDBV) and Baden-Württemberg (LGL), with the motivation to better harmonize the basis for height determination.

In these countries, the official national height reference systems that are still in use apply different definitions of the height and the zero levels refer to different tide gauges and epochs. Additionally, the treatment of the permanent tide is not fully consistent. This causes differences at the decimeter scale which also vary along the national borders. At the same time, Austria and Switzerland do compute and store also EVRS-compatible geopotential numbers that are valuable for height system unification.

The ambitions of the initiative therefore mirror the situation as described above ‒ to foster and to intensify the cooperation between the partners regarding regional gravity field modeling and to provide better information about the transformations between the national height systems.

It was agreed that the cooperation should first focus on a case study area around Lake Constance, with envisaged extension to the complete territories of the “D-A-CH countries” and/or, ideally, to the most of the European Alps. The following achievements have been reached for the focus area:

In view of these developments, and taking into account that these challenges are not unique for this specific area, it is planned to extend this initiative to the computation of the entire European Alps (and surrounding lowland areas) and rename the project to “European Alps Geoid (EAlpG)”.

We believe that this project can contribute to a better understanding of height differences across borders. Such height differences are for instance of great interest for ground water level investigations or flood protection. Other crucial applications for cross-border height unification are engineering projects such as tunnels, bridges, supply lines, etc.

What is more, these activities shall be embedded in a pan-European geoid initiative within EUREF. Contributing to the upcoming EUREF Working Group “European Height Reference Surface”, the European Alps Geoid will be one of many cornerstones to build an official EVRS height reference surface.

Potential cooperation partners have been contacted. Nevertheless, the initiative shall be open to interested parties. A virtual meeting is planned to be held shortly after the vEGU2021.