High-precision profile for geoid validation in the FCC region at CERN

Abstract

The Large Hadron Collider (LHC), the biggest collider of its type, is reaching its conclusion by 2040. In the scope of initial studies for a post-LHC particle accelerator, the design and feasibility of the Future Circular Collider (FCC) at CERN, with a circumference of around 100 km, are studied until 2025/2026. In the FCC-Geodesy project, that belongs to these initial studies, the reference network on the surface and in the tunnel is under development and a new high-precision geoid model for the significantly larger FCC area will be computed. The alignment of the magnets and thrusters in the tunnel requires a high-precision geoid model with a precision of 30 μm over 225 m. Therefore, we established a 40 km long geoid profile for the assessment of existing and more precise geoid models to be derived in the future for the region. This profile runs in a North-South direction through the area of interest and crosses the French-Swiss boarder twice. In several measurement campaigns in 2021 and 2022, measurements at a spacing of approx. 1 km along the profile were carried out collecting 1) astro-geodetic deflections of the vertical (DoV) with the CODIAC zenith camera, 2) spirit levelling for height determination, 3) corresponding gravimetric measurements and 4) GNSS measurements during two sessions of about 24 hours on 36 semi-permanent points in order to firstly obtain accurate positions for all measurement points and secondly to calculate an ultra-precise GNSS/levelling profile. This poster will present the objectives of the FCC-Geodesy project and the first results of this high-precision profile for geoid model validation.