Improving Wet Refractivity Estimation via GNSS Tropospheric Tomography: A Case Study in the Northwest and North of Iran

Abstract. Water vapor plays a critical role in atmospheric processes, yet its dynamic nature poses challenges for accurate measurement. Traditional methods like radiosondes lack sufficient spatial and temporal resolution, prompting the use of Global Navigation Satellite Systems (GNSS) tomography for improved wet refractivity estimation. This study investigates the feasibility of GNSS tomography in northern and northwest Iran, leveraging data from 20 GNSS stations and radiosonde measurements from Tabriz and Tehran. A voxel-based tomographic model was employed, with horizontal resolutions of 0.37°–0.5° and vertical resolutions of 500–1000 m. The results were validated against radiosonde data, revealing Root Mean Square Error (RMSE) values ranging from 1.58 to 2.91 ppm in Tabriz and 2.02 to 2.16 ppm in Tehran. These findings demonstrate the potential of GNSS tomography to complement traditional methods, particularly in regions with sparse observational networks. The study highlights the importance of optimal voxel resolution and geometric constraints in enhancing tomographic accuracy, offering a promising approach for regional weather monitoring and climate research.