Unraveling the Accuracy Enigma: Investigating ZTD Data Precision in TUW-VMF3 and GFZ-VMF3 Products Using a Comprehensive Global GPS Dataset

Tropospheric delay is one of the major error sources for space geodetic techniques, such as the global navigation satellite systems (GNSSs). The accurate priori zenith tropospheric delay (ZTD) information is of crucial importance for the accuracy of positioning and navigation and for reducing the convergence time in GNSS data processing. This article conducted the first global spatiotemporal assessment of two existing tropospheric products from Vienna University of Technology (TU Wien, TUW) and the GeoForschungsZentrum Potsdam (GFZ), namely, TUW-Vienna Mapping Function 3 (VMF3) and GFZ-VMF3. The referenced ZTD data used in this study are sourced from a screened ZTD dataset created by the Karlsruhe Institute of Technology (KIT) team in 2020, which obtained 91 088 258 screened ZTD values from 12 552 GNSS stations. The results revealed that the two products exhibited high similarity with RMSE/Bias of 16.47/−3.62 and 17.63/−2.23 mm for the TUW-VMF3 and GFZ-VMF3, respectively. Their different performances were also clearly observed from the analysis of the geographical distribution, season, and epochs. The TUW-VMF3 outperformed GFZ-VMF3 at 70.1% stations, but noted that in the European region, the GFZ-VMF3 was superior to the TUM-VMF3. In the regions of North America and Japan, both products exhibited better performance in winter, but in other regions, this seasonal trend was less pronounced. TUW-VMF3 performed better in case #1 without interpolation for two products, and GFZ-VMF3 performed better in case #2, where only TUM-VMF3 required interpolation. In case #3, where both required interpolation, TUW-VMF3 exhibited better with an RMSE of 15.59 mm, although GFZ-VMF3 outperformed in seven epochs.