Three-Dimensional Refractivity Model for Atmospheric Mitigation in Distance and Vertical Angle Measurements

Atmospheric refraction is a significant challenge to accurate distance and angle measurements in open-air environments, often limiting the precision of measurements obtained using electro-optic geodetic instruments despite their nominal accuracies. This study introduces a novel model, 3D-RM, designed to mitigate atmospheric effects on both distance and vertical angle measurements. The 3D-RM integrates in situ meteorological data from a network of automatic data-loggers, terrain information from a digital terrain model (DTM), and sensible heat flux from the fifth generation of European Centre for Medium-Range Weather Forecast reanalysis (ERA5), which is used in the application of the Turbulence Transfer Model (TTM) for estimating vertical refractivity gradients at various height levels. The model was tested with total station observations to 10 target points during two field campaigns. The results show that applying the model for distance correction leads to improvements in terms of closeness to reference values when compared to the standard method, which relies only on meteorological data collected at the station. Furthermore, the model has been additionally tested by removing the station meteorological data (3D-RM2). The results demonstrate that accurate corrections can be obtained even without the need of meteorological sensors specifically installed at the station point, which makes it more flexible. The 3D-RM is a cost-effective and relatively easy-to-implement solution, offering a promising alternative to existing methodologies, such as measuring meteorological values at both station and target points or the development of new instruments that can compensate the refractivity (such as a multiple-color electronic distance meter).