Assimilating Ground-Based and High-Dynamic Airborne GNSS Zenith Total Delays Into Numerical Weather Predictions

The assimilation of ground-based Global Navigation Satellite Systems (GNSS) zenith total delays (ZTDs) has been demonstrated to benefit meteorological applications such as weather forecasting and monitoring. However, their effects are limited by the restricted three-dimensional spatial resolution especially in the vertical direction. Fortunately, the fast-developing unmanned aerial vehicle (UAV) market offers an opportunity to obtain airborne GNSS ZTDs that contain atmospheric information at different locations. Given their unprecedented vertical coverage and spatial resolution, it is promising to assimilate them and further improve numerical weather predictions (NWPs), which, however, has not been investigated and thus still unclear to the community. In this paper, we obtained UAV-based GNSS ZTDs and assimilated them using the WRFDA package, with ERA5 and radiosonde as references to evaluate ZTD and relative humidity (RH) accuracy. Our results show that assimilating airborne GNSS ZTDs improved the humidity field, with RMSE and bias decreasing by up to 22% and 57%, respectively, compared to merely assimilating ground-based GNSS ZTDs. The improvements are more significant with a higher spatial-temporal resolution of the airborne observations. This study contributes to further expanding the application of GNSS meteorology and offers initial ideas for using airborne GNSS to benefit weather forecasts.