Development of a New Tabular Zenith Tropospheric Delay Model for Real-Time GNSS Applications

The tropospheric delay is a major error source for Global Navigation Satellite System (GNSS) positioning and navigation, and usually can be corrected by using an empirical model. Due to the small number of parameters and simplified algorithm, the UNB3m model has been widely hardwired in GNSS receivers for real-time applications. However, many studies have noted that the UNB3m model has significant systematic errors in the correction of tropospheric delays, mainly due to the assumption of north-south symmetry. Therefore, considering the realistic atmospheric behavior, we proposed a new tabular zenith tropospheric delay (TZTD) model using 10 years of NCEP (National Centre for Environmental Prediction) data. The performance of the TZTD model was assessed along with the GPT3 and UNB3m models by comparison with ZTDs derived from the fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA5) data and GNSS observations. The results show that the TZTD model (with a RMSE of 41mm) significantly outperforms the UNB3m model (with a RMSE of 49 mm). Furthermore, the accuracy of the new model is better than that of the GPT3 model in terms of the zenith tropospheric hydrostatic delay (ZHD) prediction, particularly at high altitudes. The TZTD model characterized by simplicity and accuracy, is expected to be a substitute for the UNB3m model in real-time GNSS applications.