Development of a High-Resolution Tropospheric Delay Model Integrating GNSS ZTD and ERA5 Reanalysis

Tropospheric delay is a key metric in weather monitoring and represents one of the primary error sources in precise positioning. Advances in Global Navigation Satellite System (GNSS) and Numerical Weather Models (NWM) presents significant potential for enhancing the resolution and accuracy of tropospheric delay models. In this study, a high-resolution (5 km) zenith tropospheric delay (ZTD) model, named the Data Assimilation Model of ZTD (DAM), is developed by assimilating GNSS ZTDs into the ERA5 background field using the WRF model. Experiments are conducted in the complex terrain of the U.S. West Coast, using GNSS ZTD data from 35 test stations for validation. Comparing DAM with three other models, the results show that DAM provides the best match with GNSS ZTD, with an RMS of 5.95 mm. DAM also demonstrates high stability across different seasons, with a minimal RMS variation of approximately 0.9 mm and the lowest seasonal average RMS of 5.70 mm. When the number of modeling stations decreases from 62 to 10, DAM maintains good stability and accuracy, with the RMS increasing from 5.95 mm to 7.03 mm. In cases of uneven station distribution, the RMS value for DAM is 7.55 mm, further highlighting its superior accuracy and robustness to varying station distributions.