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Abstract

In the scope of initial studies for a post-LHC particle accelerator, the design and feasibility of the Future Circular Collider (FCC) at CERN are studied. In the FCC-Geodesy project, which belongs to these initial studies, a high-precision geoid model for the significantly larger FCC area will be computed. The pre-alignment of the magnets and thrusters in the tunnel requires a very accurate high-resolution local geoid model with a precision of 30 μm over 225 m. Therefore, we established a 40 km long validation profile for the assessment of existing and more precise geoid models derived in this project for this 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, the following measurements at a spacing of approximately 1 km along the profile were carried out: 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 approximately 24 hours on 36 semi-permanent points to calculate an ultra-precise GNSS/levelling profile as well as an astrogeodetic profile. Additionally, a first geoid model was estimated specifically for this region in a least-squares adjustment based on measurements of gravity and DoV. This talk will present the objectives of the FCC-Geodesy project, the results of the high-precision profile, the initial geoid model, and a first comparison of existing and newly calculated geoid models in this region.