Tropospheric Modeling and Fixed Stations Constraints in Precise GPS Computations: Case Study

Accurate GPS positioning requires correct modeling of tropospheric refraction, the phenomenon responsible for tropospheric delay (TD). The Niell mapping function, which is used in almost all processing packages to model TD, is being replaced by improved models. This study analyzes the influence of TD models and absolute antenna phase center variation (PCV) models. Solutions computed with the Niell mapping function and global mapping function TD models were compared at several European International Global Navigation Satellite Systems (GNSS) Service (IGS) stations. GPS sessions of 24 hours, observed on five different days in 2008, were used for this investigation. Two independent network-station constraint approaches are considered: a GPS network fixing a single station was implemented and was followed by a second network solution in which several IGS stations were constrained. The elevation-cutoff angle was set to 0° to obtain the maximum influence of the TD model at altitudes close to the horizon. Result...