Assessment and implementation of NOAA NWP-based tropospheric correction model

Tropospheric delay is one of the dominant Global Positioning System (GPS) errors, which degrades the positioning accuracy. Recent developments in tropospheric modeling rely on implementation of more accurate Numerical Weather Prediction (NWP) models. In North America one of the NWP-based tropospheric correction models is the NOAA model, which has been developed by the US National Oceanic and Atmospheric Administration (NOAA). Because of its potential to improve the GPS positioning accuracy, the NOAA tropospheric correction model became the focus of many researchers. In this paper, we analyzed the performance of the NOAA tropospheric correction model and examined its effect on precise point positioning (PPP) solution. We generated a three-year-long tropospheric zenith total delay (ZTD) data series for the NOAA, Hopfield, and the IGS final tropospheric correction product, respectively. These data sets were generated at ten IGS reference stations spanning Canada and the United States. We analyzed the NOAA ZTD data series and compared them with those of the Hopfield model. The IGS final tropospheric product was used as a reference. The analysis shows that the performance of the NOAA model is a function of both season (time of the year) and geographical location. However, its performance was superior to the Hopfield model in all cases. We further investigated the effect of implementing the NOAA model on the PPP solution convergence and accuracy, which again showed superior performance in comparison with the Hopfield model.