Evaluation of Real-Time ZWD and Tropospheric Gradients Derived from GFZ Real-Time Orbit and Clock Products

Precise Point Positioning (PPP) provides zenith wet delay (ZWD) and horizontal tropospheric gradients as key tropospheric parameters. The availability of real-time satellite orbit and clock products enables real-time tropospheric monitoring, which is currently mainly based on IGS Real-Time Service (IGS-RTS) products. In this study, we evaluate real-time tropospheric parameters derived from the newly released GFZ real-time orbit and clock streams. The assessment is performed using both the GFZ global station network and the regional GEONET network operated by the Geospatial Information Authority of Japan (GSI), focusing on ZWD and horizontal gradients. An analysis of one week of data in June 2025 shows that under calm meteorological conditions, real-time ZWD and gradients achieve an accuracy better than 3 mm with respect to the solution derived from GFZ final products, with a data completeness of 99.8%. A case study focusing on strong convective conditions, exemplified by typhoon events over the Pacific Ocean east of Japan in August 2025, indicates no noticeable degradation in the precision and latency of real-time ZWD and tropospheric gradients. The comparison with ultra-rapid products, which include predicted orbit and clock components, shows that real-time ZWD and gradients consistently outperform ultra-rapid solutions. Furthermore, comparisons among multiple analysis centers (ACs) show that tropospheric solutions generated using GFZ real-time streams exhibit competitive accuracy, stability, and completeness.