New publication by Zhang et al. (2025)

"Assimilating Ground-Based and High-Dynamic Airborne GNSS Zenith Total Delays Into Numerical Weather Predictions" by Zhang et al. (2025)

22.07.2025

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The assimilation of ground-based global navigation satellite system (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 3D spatial resolution, especially in the vertical direction. Fortunately, the fast-developing uncrewed 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 is thus still unclear to the community.

In this study, 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 root-mean-square error (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.

Data distribution and processing procedure for experiment-1, conducted on June 2, 2021. (a) Configuration of the three nested WRF domains. (b) Locations of ground-based GNSS stations within the innermost domain (d03). (c) and (d) Distribution of airborne GNSS ZTDs in d03, where blue, red, and green dots indicate data with temporal resolutions of 1, 5, and 10 min, respectively. (e) WRF forecasting and DA cycle, with GFS 0- and 3-h forecasts used as lateral boundary conditions. Evaluation of five assimilation cases in experiment-1 using ERA5-based ZTD and radiosonde-based RH. Five cases are: CTRL without assimilation, G with ground based ZTDs assimilation; GA cases assimilating ground and aircraft-based ZTDs of different temporal resolution in minutes. The top-left panel shows the reference ZTD field from ERA5 in the inner domain, while the remaining panels display ZTD error maps for each case, with the color bar indicating ZTD error in centimeters. The plot on the right shows the vertical profiles of RH error with respect to radiosonde observations.

Reference
Z. Zhang, M. Liu, W. Zhang, Y. Lou and B. Soja, "Assimilating Ground-Based and High-Dynamic Airborne GNSS Zenith Total Delays Into Numerical Weather Predictions," in IEEE Transactions on Geoscience and Remote Sensing, vol. 63, pp. 1-9, 2025, Art no. 4106909, doi: external page 10.1109/TGRS.2025.3583462.