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. An analysis of processing settings impacts on estimatedtropospheric gradients is presented. The study is based on the benchmarkdata set collected within the COST GNSS4SWEC action with observations from430 Global Navigation Satellite Systems (GNSS) reference stations in central Europe for May and June 2013.Tropospheric gradients were estimated in eight different variants of GNSSdata processing using precise point positioning (PPP) with the G-Nut/Tefnutsoftware. The impacts of the gradient mapping function, elevation cut-offangle, GNSS constellation, observation elevation-dependent weighting andreal-time versus post-processing mode were assessed by comparing thevariants by each to other and by evaluating them with respect totropospheric gradients derived from two numerical weather models (NWMs).Tropospheric gradients estimated in post-processing GNSS solutions usingfinal products were in good agreement with NWM outputs. The quality ofhigh-resolution gradients estimated in (near-)real-time PPP analysis stillremains a challenging task due to the quality of the real-time orbit and clockcorrections. Comparisons of GNSS and NWM gradients suggest the 3∘elevation angle cut-off and GPS+GLONASS constellation for obtainingoptimal gradient estimates provided precise models for antenna-phase centreoffsets and variations, and tropospheric mapping functions are applied forlow-elevation observations. Finally, systematic errors can affect thegradient components solely due to the use of different gradient mappingfunctions, and still depending on observation elevation-dependent weighting.A latitudinal tilting of the troposphere in a global scale causes asystematic difference of up to 0.3 mm in the north-gradient component, whilelarge local gradients, usually pointing in a direction of increasinghumidity, can cause differences of up to 1.0 mm (or even more in extreme cases)in any component depending on the actual direction of the gradient. Althoughthe Bar-Sever gradient mapping function provided slightly better results insome aspects, it is not possible to give any strong recommendation on thegradient mapping function selection.

Sensitivity of GNSS tropospheric gradients to processing options