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Introduction

The EPN-Repro3 project is the third comprehensive reprocessing campaign of the EUREF Permanent Network (EPN), undertaken to support a homogeneous, highly accurate, and up-to-date realization of the European Terrestrial Reference System (ETRS89). Since 1996, the EPN has expanded from a few dozen GPS stations to more than 420 multi-GNSS sites across Europe, making it the backbone of ETRS89. Over time, new satellite constellations, evolving antenna calibration models, and improved geophysical standards have introduced inconsistencies into long-term coordinate time series. EPN-Repro3 therefore reprocesses the entire EPN dataset from 1996 until 2022 using unified models consistent with IGS repro3 and IGS20. The result is a fully harmonized and extended dataset, providing reliable regional reference frame products essential for geodesy, surveying, geodynamics, and monitoring of long-term crustal motions.

EPN-Repro3 was implemented and executed by the EPN Reprocessing Working Group.

Processing Strategy of the EPN Analysis Centres

EPN-Repro3 followed a coordinated processing strategy designed to ensure uniformity, redundancy, and compatibility with the IGS repro3 processing standards. Twelve EPN Analysis Centres (ACs) participated, each responsible for processing a sub-network of stations so that every GNSS station was evaluated independently by at least three ACs, increasing reliability and enabling rigorous cross-validation. All ACs used the same fundamental modelling conventions and antenna calibration models—exclusively type-mean antenna calibrations, ensuring consistency with IGS20 and avoiding heterogeneities caused by older individual calibrations. The data analysis procedure for EPN-Repro3 is consistent with the routine EPN analysis procedure, see Guidelines for EPN Analysis Centres.

Participating Analysis Centres

The processing used GPS, GLONASS, and Galileo data. Ten ACs used Bernese GNSS Software 5.4, while GFZ employed EPOS-P8 and MUT used GAMIT. Each AC conducted internal quality control, removed outliers, and validated metadata before submitting SINEX files to the EPN Analysis Centre Coordinator (ACC). The ACC then performed additional screening and requested corrections where needed.

Responsibilities of the EPN Analysis Centre Coordinator (ACC)

The EPN Analysis Centre Coordinator (ACC) plays a central role in transforming the large number of individual AC solutions into a consistent, validated, and high-quality combined product. After receiving the daily SINEX solutions from the 12 ACs, the ACC performs an extensive multi-stage combination procedure.

In the first stage, the ACC checked the station metadata included in each daily AC SINEX file, and in case of detected errors - such as incorrect antenna or radome codes - reported them back to the ACs for correction. In the second stage, the ACC stacked individual AC daily solutions into long-term solutions using the CATREF software, enabling the detection of station position outliers, and discontinuities. Outliers beyond a certain level were removed from AC solutions.

In the next stage, the ACC combined the cleaned daily solutions of every AC at the normal-equation level. The combination was repeated until no further outliers remained, after which the daily combined solutions were aligned to IGS20.

Finally, the ACC evaluated the combined daily solutions by stacking them into a new long-term solution to remove remaining inconsistencies, and then generated the weekly combined solutions.

The ACC also produced detailed text and YAML reports documenting residuals, excluded stations, metadata errors, AC-specific issues, and other diagnostics. Through these steps, the ACC ensured that EPN-Repro3 delivered a robust, fully validated, and internally consistent reference frame product.

Products of EPN-Repro3

EPN-Repro3 provided a comprehensive set of daily and weekly GNSS products that followed the IGS20 conventions and the new long-filename standard introduced by the IGS.

Products Produced

• Daily station coordinates (SINEX):
  EUR0E03SNX_YYYYDDD0000_01D_01D.SOL.SNX
• Daily combination reports (text and YAML):
  EUR0E03SNX_YYYYDDD0000_01D_01D.SUM.SUM and
  EUR0E03SNX_YYYYDDD0000_01D_01D.SUM.YML
• Weekly coordinate solutions (SINEX):
  EUR0E03SNX_YYYYDDD0000_07D_07D.SOL.SNX
• Weekly summary reports (SINEX):
  EUR0E03SNX_YYYYDDD0000_07D_07D.SUM.SUM

These files contain station positions and covariances, information about excluded stations, RMS statistics, metadata checks, and details of the combination strategy.

Data Availability

The products are made openly available at the official EPN data centres:

• BKG GNSS Data Centre (Germany)
  https://igs.bkg.bund.de/root_ftp/EUREF/products/
• BEV GNSS Data Centre (Austria)
  https://gnss.bev.gv.at/at.gv.bev.dc/data/products/

These repositories host the complete set of daily and weekly EPN-Repro3 solutions from 1996 to 2022, along with accompanying documentation.