EUREF Permanent Network Stations Research Articles

Quasi-4-dimension ionospheric modeling and its application in PPP

Ionospheric delay modeling is not only important for Global Navigation Satellite System (GNSS) based space weather study and monitoring, but also an efficient tool to speed up the convergence time of Precise Point Positioning (PPP). In this study, a novel model, denoted as Quasi-4-Dimension Ionospheric Modeling (Q4DIM) is proposed for wide-area high precision ionospheric delay correction. In Q4DIM, the Line Of Sight (LOS) ionospheric delays from a GNSS station network are divided into different clusters according to not only the location of latitude and longitude, but also satellite elevation and azimuth. Both Global Ionosphere Map (GIM) and Slant Ionospheric Delay (SID) models that are traditionally used for wide-area and regional ionospheric delay modeling, respectively, can be regarded as the special cases of Q4DIM by defining proper grids in latitude, longitude, elevation, and azimuth. Thus, Q4DIM presents a resilient model that is capable for both wide-area coverage and high precision. Four different sets of clusters are defined to illustrate the properties of Q4DIM based on 200 EUREF Permanent Network (EPN) stations. The results indicate that Q4DIM is compatible with the GIM products. Moreover, it is proved that by inducting the elevation and azimuth angle dependent residuals, the precision of the 2-dimensional GIM-like model, i.e., Q4DIM 2-Dimensional (Q4DIM-2D), is improved from around 1.5 Total Electron Content Units (TECU) to better than 0.5 TECU. In addition, treating Q4DIM as a 4-dimensional matrix in latitude, longitude, elevation, and azimuth, whose sparsity is less than 5%, can result in its feasibility in a bandwidth-sensitive applications, e.g., satellite-based Precising Point Positioning Real-Time Kinematic (PPP-RTK) service. Finally, the advantages of Q4DIM in PPP over the 2-dimensional models are demonstrated with the one month's data from 30 EPN stations in both high solar activity year 2014 and low solar activity year 2020.

Offsets in the EPN station position time series resulting from antenna/radome changes: PCC type-dependent model analyses

The EUREF Permanent Network (EPN) currently consists of more than 300 evenly distributed continuously operating Global Navigation Satellite System (GNSS) reference stations. As a result of the continuous modernization of GNSS systems, the equipment of reference stations is subject to changes and upgrades. Changes relating to GNSS receiver antenna replacement are considered the main reason for discontinuities noticed in station position time series. It is assumed that resulting offsets are primarily caused by changes in carrier phase multipath effects after antenna replacement. However, the observed position shifts may also indicate the deficiency in the antenna phase center corrections (PCC) models. In this paper, we identified and interpreted the coordinate shifts caused by antenna/radome changes at selected EPN stations. The main objective was to investigate the correlation between the offset occurrence and PCC model type (type mean, individual robot-derived, individual chamber-derived) as well as multipath changes after antenna replacement. For the study, GNSS data from 12 EPN stations covering the years 2017–2019 were analyzed. The results proved that the antenna replacement is critical in the context of station coordinates stability and, in most cases, results in visible shifts in the position component time series. For GPS-only solutions, the most stable results were achieved using robot-derived individual PCC models. On the other hand, in the case of GPS + Galileo processing, the most stable results were obtained using chamber-derived individual PCC models. Furthermore, discontinuities due to the antenna change were noticed in the position time series in 75% of GPS + Galileo solutions. On the other hand, multipath changes arising as the result of antenna replacement were responsible, depending on solution type, for 21–42% of variations in the coordinates.

GNSS metadata and data validation in the EUREF Permanent Network

The EUREF Permanent Network (EPN) is a network of continuously operating GNSS stations installed throughout the European continent. The EPN Central Bureau (CB) performs the day-to-day EPN coordination, acts as liaison between station operators, data centers, and analysis centers, and maintains the EPN Information System. Over the last years, the EPN CB has accommodated the enhancements required by the new EU General Data Protection Regulation, new multi-GNSS signals, new RINEX formats, increased usage of real-time GNSS data, and the new GeodesyML metadata exchange format. We will discuss how the EPN CB validates and provides access to EPN station metadata and monitors EPN data sets in terms of availability, latency, and quality to ensure they meet the user requirements. The analysis of 23 years of EPN GNSS data quality checks demonstrates some of the most frequently encountered tracking problems affecting EPN stations, and specific GNSS receiver types, throughout the years.

Periodic signals in a pseudo-kinematic GPS coordinate time series depending on the antenna phase centre model – TRM55971.00 TZGD antenna case study

This study investigates the differences between position estimates obtained using individual and type-mean (igs08.atx) antenna calibration models in GPS pseudo-kinematic processing. We used 15-min observation windows to study the short-period oscillations. Continuous GPS observations from eight selected Polish EUREF Permanent Network stations with the same TRM55971.00 TZGD antenna were used. The results showed that the differences in the calibration models, directly propagate into the position domain, affecting sub-daily results and influencing periodic variations. The sub-daily variations have periods close to half a sidereal day with amplitudes of up to 10 mm in position components. It could also be demonstrated that the mean position offsets, resulting from the use of individual calibrations instead of type-mean igs08.atx calibrations, can reach up to 5 mm in the up component, while the offsets in the horizontal components generally remain below 1 mm.

GEOSUD/SUDETEN network GPS data reprocessing and site velocity estimations

The geodynamic network of the Sudety Mts. (GEOSUD) was established in Poland in 1996. Simultaneously, the geodynamic network EAST SUDETEN was built on the Czech side in 1997 and, in 2001, it was extended for sites towards west (the WEST SUDETEN network). Since 1997 annual GPS campaign measurements have been performed on GEOSUD and EAST SUDETEN networks. Satellite observations were processed several times using the Bernese GPS Software, versions 4.0, 4.2 and 5.0. Different observation periods were processed applying different models for Earth's rotation, satellite ephemeris, pole motions, ocean loadings and antennas calibrations. This paper describes the result of uniform reprocessing of all measurements carried out in the period 1997-2012. The Bernese GPS Software V5.0 supported by the IGS Final product and absolute antenna phase centre model (IGS Final from 1409 GPS week (REPRO1 from 920 to 1408)) was used for the homogeneous reprocessing. The solution was referenced to the ITRF2008 datum using data from class A stations of the EUREF Permanent Network (EPN). The GEOSUD network was processed at IGG and the EAST and WEST SUDETEN networks at IRSM applying common processing strategy and the same reference EPN stations. Horizontal site velocities were estimated in a minimum constrained solution using ADDNEQ2 module of the Bernese GPS Software V5.0. The ITRF2008 a priori coordinates and velocities were introduced for fiducial stations belonging to EPN network. Estimated ITRF2008 velocities quality assessment was also performed by the comparison with reference EPN and ASG-EUPOS velocities. Final velocities were transformed to the ETRF2000(R08) applying the ITRF2008 plate-motion model. Paper summarizes the horizontal velocity estimations of the GEOSUD, EAST and WEST SUDETEN geodynamic network sites that cover the Sudety area and their tectonic foreland. ARTICLE INFO

Regional densification of the IGS in europe using the EUREF permanent GPS network (EPN)

In 1995 EUREF took the initiative to coordinate the activities related to existing permanent GPS stations in Europe and created the EUREF Permanent Network (EPN) for the maintenance of the European Terrestrial Reference System (ETRS89).Presently, the data from most of the EPN stations is available within a 24-hour delay and additionally one third of the stations provides hourly data. The performance evaluation of the EPN data flow indicates that the reliability of the hourly data flow and the development of fallback procedures in case of unreachable data centres are requiring further improvements. Half of the EPN stations belong to the IGS network and as a consequence, improvements of latency, availability and reliability within EUREF will benefit the IGS too.Each of the twelve analysis centres process part of the EPN and obtain weekly estimated coordinates and their covariance info. The combination of these individual solutions constitutes the EPN weekly combination. The quality of this solution is in average 1.6, 1.7 and 4.9 mm for the North, East and up components, respectively.A multi-year combination of the weekly EPN solutions was submitted to IERS for inclusion into the ITRF2000. As a first accuracy assessment this solution was compared to the ITRF2000 contribution of CODE and showed to be consistent with the internal precision of the weekly solutions.The establishment of an EPN Coordination Group, in June 2000, allows the continuation of an efficient management of the expanding GPS tracking network and the growing array of related multi-disciplinary projects.