The Global Climate Observing System (GCOS) Reference Upper Air Network (GRUAN, https://www.gruan.org/ ) of the World Meteorological Organization (WMO) is an international observing network, designed to meet climate requirements. Upper air observations within the GRUAN network will provide long-term high-quality climate records. A GNSS receiver is part of the GRUAN station equipment with highest priority for measuring of atmospheric water vapor.

GRUAN observations are intended to provide long-term high-quality data for the reliable determination of climatological trends and to provide further insight into atmospheric processes. Precise GNSS data analysis is a key to reach data quality on the highest level. Due to its long-term experience in GNSS data processing, GFZ was selected as a Central GRUAN GNSS Data Processing Centre.

This data publicatoion includes the GRUAN Data Product (GDP) of GFZ: GNSS Precipitable Water (PW).

GFZ GRUAN Processing Centre generates Precipitable Water (PW) products for GNSS sites of the GRUAN network using the latest development version of the EPOS.P8 Software.

The solution series contains:
Precipitable Water (PW), converted from the Zenith Total Delays (ZTD)
Folder sinex_trop_GRUAN_EPOS8 with subfolders for GPS weeks (e.g., w2348): daily files for each processed GNSS site.

Files:
IIIIWWWWD.tro: files with Zenith Total Delays, Precipitable Water (also called Integrated Water Vapor), tropospheric gradients;
IIIIWWWWD.zpd: files with Zenith Total Delays and tropospheric gradients;

where
IIII - GNSS site name,
WWWW - GPS week,
D - day of the week;

Data format: SINEX_TRO: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5030246
The processing with EPOS.P8 is described in detail in Wang et al. (2019).