Multidimensional Assessment of the VMF3-FC and Its Application in PPP-IAR

Tropospheric delay is a major error source in Global Navigation Satellite System (GNSS), and the accuracy of its modeling critically influences positioning performance. In this study, we evaluate the performance of the real-time tropospheric correction model, VMF3-FC, under diverse geographic and climatic conditions. Both site-wise and grid-wise products at multiple spatial resolutions are assessed, with a particular focus on the widely used 1°×1° and 5°×5° products. Using IGS-ZTD as the reference, results show that the root mean square (RMS) of ZTD is approximately 1.58 cm for site-wise products, 1.67 cm for the 1°×1° products, and 2.34 cm for the 5°×5° products. VMF3-FC maintains stable performance across seasonal changes and during typhoon events, with no significant accuracy degradation as forecast duration increases. Further GNSS evaluation reveals that incorporating VMF3-FC as tropospheric constraints significantly enhances integer ambiguity resolution (PPP-IAR) performance, yielding a 23% improvement in vertical accuracy and a 4.27% reduction in convergence time. For traditional Precise Point Positioning (PPP) float solutions, the improvements are modest, with horizontal accuracy gains below 0.2%, vertical improvement of 5.2%, and a 1.1% reduction in convergence time. Overall, VMF3-FC demonstrates high accuracy and robustness, making it a reliable correction model for GNSS positioning and atmospheric studies. Its broad applicability underscores its value in geospatial information science and real-time navigation systems.