Impacts of atmospheric turbulence on optic measurements over heterogeneous flat terrain: insights from large eddy simulations.

Atmospheric refraction imposes a fundamental limitation on the accuracy and precision of geodetic measurements that utilize electromagnetic waves. For terrestrial observations at optical wavelengths recorded over flat terrain, the vertical temperature gradient controls the bending of the rays thus affecting mostly the vertical angle measurement. The rules of thumb for mitigating these effects (variation ranges and short-term fluctuations) are based on intuition and practitioner experience. To address the challenge of understanding the impact of refractive index inhomogeneities on the refraction angle without additional instruments, we introduce large eddy simulations (LES) in geodesy. We use the PALM software to simulate realistic atmospheric conditions and investigate first- and second-order variations of the refraction angle using virtual measurements over a flat terrain with surface heterogeneities. We analyze the optimal measurement times to minimize refraction effects, highlighting the potential of LES to help plan measurement campaigns. Additionally, the correlating influence of atmospheric turbulence on the measurements is quantified. We propose a correction model based on the variance inflation factor as a practical tool for incorporating turbulence into a geodetic uncertainty model.