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Abstract

Accurate tropospheric delay models are important for spatial observations. However, different tropospheric mapping functions vary widely at low elevation angles, causing difficulties for geodetic users to select the right one for precise positioning. Focused on four commonly used tropospheric mapping functions, we carry out a detailed analysis by solving both tropospheric delay and surface displacement results at 3°, 5°, and 7° elevation angles for 89 IGS stations from 2018-2021. Our results confirm that the discrepancies in the tropospheric delay results from different mapping functions become larger with decreasing elevation angle, and the noise also becomes larger. Among them, the differences between NMF and VMF1 results are the largest, reaching 6 mm for station MAL1 at the 3° elevation angle, while there is also trend difference of mostly less than 3 mm/year for the tropospheric delay time series. Besides, there are multiple peaks in the station displacement difference series obtained from different mapping functions in the U-direction, and each peak is not exactly symmetric to the median or mean value. In comparison with, the coordinate range for the U-component at the 7° elevation angle is narrowed by more than 50% compared with that from the 3° elevation angle results. Another interesting phenomenon is that there exist systematic difference in the results of these groups. As a whole, VMF3 and GMF are recommended for solving tropospheric delays, VMF3 and VMF1 are better for solving reference station coordinate time series, while NMF performs a little worse at middle and high latitudes.