The European Alps Geoid (EAlpG) Project – a joint initiative for improved cross-border regional geoid modelling and height transformation

The official national height reference systems 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 entirely consistent. This causes differences at the decimetre scale, which also vary along the national borders. The "European Alps Geoid Project" (EAlpG) aims to harmonize the basis for height determination in the Alpine region, including the neighbouring lowlands and the computation of a uniform geoid model according to European standards for height and positioning.

The project is based on the experiences and findings of the predecessor "D-A-CH geoid" project, which covered a test area around Lake Constance. It was a joint initiative of the federal and state authorities responsible for land surveying in Germany, Austria and Switzerland.

First steps of the EAlpG project were the conclusion of the Memorandum of Understanding in May 2022 as well as the initiation of the exchange of gravity and height data. The ambitions of the initiative are therefore to intensify the cooperation’s between the partners in regional gravity field modelling and to provide better information on the transformations between the national height systems. The following activities are planned:

1. Improved cross-border regional geoid model of the Alpine area:

• Revision and harmonization of the base data for the calculation of the geoid models: gravity data, digital elevation models, control points for validation
• Cross-border gravity measurements, e.g. Austria, France, Germany, Italy, Switzerland
• Comparative studies on geoid modeling in high mountains

2. Improved height transformation between the Alpine countries:

• Extensive comparative investigations and validation between the national height reference surfaces (geoid models and other height transformation grids) and the national and European heights along the borders
• Derivation of consistent height transformation models accurate to a few centimeters
• Development of a corresponding web application

The outcomes of the project will support (non-)geodetic users in there cross-border height applications, e.g. ground water level investigations, flood protection. Other important applications for cross-border height standardisation are engineering projects such as tunnels, bridges, supply lines, etc.

The results will 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.

The EAlpG project is a joint initiative of the national authorities and organization responsible for or involved in the integrated geodetic spatial reference of Austria, Czech Republic, France, Germany, Hungary, Italy, Slovakia, Slovenia and Switzerland. The scientific work is supported by various universities in the Alp area.