EPOS-GNSS, precise point positioning processing

Context

EPOS
EPOS (European Plate Observing System) is a multidisciplinary research infrastructure that produces data and services for the Earth Science research community.

EPOS-GNSS
The EPOS-GNSS or ‘GNSS Data and Products’ group is an EPOS component that brings together 12 partners across Europe and aims to archive and disseminate GNSS (Global Navigation Satellite System) data from permanent stations throughout Europe (using the RINEX international exchange format), software tools, as well as derived products (daily solutions, position time series, velocity fields, and deformation fields).

EPOS in Operational Phase
EPOS began with an Implementation Phase (EPOS-IP, 2015–2018). At that time, a prototype solution was produced by OSUG/ISTerre. After a Pilot Operational Phase, EPOS entered its Operational Phase in 2023.

GNSS Products over Europe

Description of the UGA / ISTerre solution
The OSUG/ISTerre processing centre first generates position time series using the JPL (Jet Propulsion Laboratory) GipsyX tool. The solutions are calculated using the precise-point-positioning approach. A complete processing was carried out in 2025-2026, and daily automatic processing is performed to keep the time series up to date.

Next, the time series are analysed to estimate position offsets (position changes due to a change in the instruments used or a high-magnitude earthquake close to the site). These offsets are available on the EPOS-GNSS product portal, in Data Controls / Offsets.

Finally, the time series are analysed to estimate secular GNSS velocities.

GipsyX PPP processing at UGA

The GipsyX processing tool analyses signals emitted by satellites orbitting the Earth (GPS and Galileo constellations), using numerous data/models as input, such as atmospheric corrections (tropospheric and ionospheric delays) and satellite orbits (final when available, rapid for daily calculations). The process therefore requires the application of sophisticated mathematical models to achieve a final position with millimeter accuracy. The parameters used for this processing are listed in the table below :

Table 1 : Processing parameters

The first solution published at the end of March 2026 comprises 1,805 stations across Europe and includes data covering a 26-year period (2000-2025 included). The database consists of all stations with data distributed via the EPOS-GNSS data portal : the stations are located in over 50 countries.

Returning to the estimation of velocities, following technical validation, the MIDAS software emerged as an effective, rapid and appropriate method. This software is an automatic estimator of time series trends (Blewitt et al., 2016). Using a statistical method based on a set of pairs of positions separated by one year, it provides GNSS velocities that are relatively insensitive to outliers, jumps and seasonal signals.

Maps of horizontal and vertical velocities

Three categories of robustness for MIDAS velocities have been defined. Robustness is quantified using two MIDAS control points :
– the maximum number of outliers that can be tolerated.
– the number of offsets (changes in position from one day to the next, mainly due to changes in instruments) depending on the duration required to maintain a reliable velocity estimate.
(For more information on MIDAS and the two MIDAS control points, see Blewitt et al., 2016).

We eliminate stations from our analysis for which MIDAS control points are not satisfied. In addition, we eliminate stations for which the error estimated by MIDAS exceeds the following values :
– horizontal error > 0.5 mm/yr
– vertical error > 1.5 mm/yr
This sorting mainly concerns sites for which the time series is too short to properly constrain the velocity estimate.

Obtaining the solutions (i.e. time series and velocity field)
All the products generated by the analysis centre (time series of positions, offsets and velocity field) will soon be available via the EPOS-GNSS product portal.
The time series will also be available on the FormaTerre ‘Geodesy Plotter’ portal (solution UGA_Epos-Fr_PPP).

European partners
UBI (Portugal), ROB (Belgium), OCA (France), CNRS (France), INGV (Italy), SGO (Hungary), BKG (Germany), LM (Sweden), WUT (Poland), LRU (France), NOA (Greece), OGS (Italy).

ISTerre-OSUG team
Anne SOCQUET, Observatory Physicist
Andrea WALPERSDORF, Observatory Physicist
Gaël JANEX, Research Engineer

Contact
Anne SOCQUET

Funding
European Research Infrastructure EPOS

Links
EPOS
EPOS-France
RENAG