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EPOS-GNSS double-difference processing
Context
EPOS
EPOS (European Plate Observing System) is a multidisciplinary research infrastructure that delivers data and services to the Earth Sciences community.
EPOS-GNSS
The "GNSS data and products" group brings together eight European partners. Its goal is to record and distribute GNSS data from permanent stations throughout Europe (Rinex files) and related products (daily solutions, position time series, velocity and deformation fields). OSUG/ISTerre hosts one of the two EPOS-GNSS data processing centers.
EPOS-Implementation Phase, then EPOS Pilot Operational Phase
EPOS started with an Implementation Phase (2015 - 2018). As part of EPOS-IP, a prototype solution was produced by OSUG/ISTerre.
EPOS has entered the Pilot Operational Phase in 2019, that will continue until 2022.
Description of the current solution
The interactive map below shows the permanent GNSS stations currently included in the OSUG/ISTerre solution. It consists of 615 stations throughout Europe and includes all data over a 22-year period (2000-2021). The database is composed of all stations which have their data currently distributed through the EPOS-GNSS data gateway :
– EPN and IGS stations
– stations from 43 local networks across 26 European countries.
Interactive map with time series data sets
Maps of horizontal and vertical velocities
Horizontal velocities with regard to the Eurasian plate. This velocity field is composed of the 576 stations which fulfill the quality criteria defined in the text below.
Maps of vertical velocities
Maps of vertical velocities (focus on the Alps and Apennines)
The massive processing implementation requires innovative strategies in order to satisfy the efficiency, robustness and automation criteria for the computation of another usual GNSS product: the velocity field.
After a technical validation, MIDAS software appeared to be the most appropriate tool. This software includes an automatic estimator of time-series trend (Blewitt at al., 2016). By using a statistical method based on a set of position pairs separated by one year, it produces GNSS velocities with very low sensitivity to outliers, steps and seasonality.
Three robustness categories on MIDAS velocities have been defined. The robustness quantification is done through two MIDAS breakdown points:
– the maximum number of large outliers that can be tolerated.
– the threshold of large steps as a function of the time span to maintain a reliable velocity estimate.
(To know more about MIDAS and the two MIDAS breakdown points, see Blewitt et al., 2016).
We eliminate from our analysis the stations for which the breakdown criteria were not satisfied. In addition, we eliminate the stations for which the error estimated by MIDAS is superior to the following error values:
– horizontal error > 0.5 mm/yr
– vertical error > 1.5 mm/yr
As a result, the maps above show velocities for 576 stations, while 39 stations were excluded.
Solutions files
Solutions (position time series and velocity field) are available through the EPOS-GNSS products portal.
For the RENAG (National GNSS network of French research laboratories) stations, the solutions are also available on the RENAG website.
European partners
UBI (Portugal), ROB (Belgium), NOA (Greece), GOP (Czech Republic), CNRS (France), INGV (Italy), IMO (Iceland), LTK (Hungary), KOERI (Turkey), INCDPM RA (Romania), LM (Sweden), BAS (Bulgaria), BKG (Germany)
ISTerre-OSUG team
Anne SOCQUET, OSUG physicist
Andrea WALPERSDORF, OSUG physicist
Gaël JANEX, Research engineer
Contact
Anne SOCQUET
Funding
EPOS European Research Infrastructure