Regional Reference Network Enhanced Tropospheric Modeling and Non-Nominal Troposphere Monitoring for GBAS in Air Transportation

The non-nominal troposphere induced by climate extremes poses a threat to the precision approach and landing of the civil aircraft in ground-based augmentation system (GBAS). However, there is currently no effective non-nominal troposphere monitoring method at both GBAS stations and aircrafts, which increases the integrity risk. This study proposes a novel approach for simultaneously modelling and monitoring ground station and aircraft non-nominal troposphere using precision point positioning (PPP) technology based on a regional reference network. The global navigation satellite system (GNSS) and meteorological data from the Hong Kong satellite positioning reference station network and numerical weather models from the European centre for medium-range weather forecasts are processed in all the year of 2017. A tropospheric correction (TC) model is used to correct station height-induced biases in zenith total delay (ZTD) obtained from PPP. By comparing the performance of 6 typical spatial interpolation algorithms in tropospheric delay interpolating, the universal Kriging algorithm is found to be the most suitable one which achieves a minimum mean absolute error (MAE) of 8.24 mm. The non-nominal troposphere is monitored using the constructed corrected ZTD map using universal Kriging method. A non-nominal troposphere up to 50 mm is observed, which can affect the integrity of the air navigation. Furthermore, the relationship between non-nominal troposphere and the rainfall is investigated. The study integrates widely distributed GNSS and meteorological data into a seamless non-nominal tropospheric monitoring service, enhancing the integrity of GBAS in air transportation.