On the Improvement of Precise Point Positioning augmented with tropospheric ZWD using CORS networks applied to bridge monitoring

In Scenarios where GNSS Double Differencing, using a permanent base station located close to a structure, is not appropriate or during periods where such a base station experiences failure then Precise Point Positioning (PPP) is quickly developing into a viable alternative option for structural monitoring applications. However, Precise Point Positioning still has limitations in terms of the accuracy and precision that can be achieved. These limitations in quality restrict the types of applications that PPP is suitable for in Structural Health Monitoring. In this paper the PPP processing algorithm is augmented using a tropospheric correction method that improves that quality of PPP positioning and is then applied to structural monitoring of large bridges. Local Continuously Operating Reference Stations (CORS) are used to estimate the troposphere correction from the undifferenced observations. These tropospheric corrections are then interpolated to provide corrections for the PPP processing at the bridge surveying point. The results show an improvement in the terms of RMSE and correlation coefficient obtained after the PPP augmentation by tropospheric correction is applied, compared with regular PPP. GPS double differenced time series are treated as the truth to assess the regular and augmented PPP solutions with various cut off angle configurations. The experimental results reveal that the deflection precision of regular PPP severely depends on the satellite geometry. Tropospheric correction augmented PPP can improve standard PPP algorithms position time series due to poor satellite geometry and expedite the carrier phase ambiguity convergence.