In 2003 the EUREF Technical Working Group (TWG) has launched the EUVN Densification Action to establish a continental homogeneous GPS / levelling database consistent with ETRS89 and the EVRS.
EUVN-DA and the related database is designed to
- help identifying the geoid, GPS or levelling errors
- provide an improved continental reference for height determination with GPS
- help understanding of the gravimetric and GPS / levelling geoid differences
- serve datum information to the European geoid determination
- support the future realization(s) of the continental height reference surface.
The National Mapping Agencies were generously supported the project, they provided existing, updated or newly measured data sets. As of Winter 2009, 25 countries participate, and the database contained more than 1400 GPS / levelling points.
EUVN-DA has been closed in 2009, however the maintenance of the EUVN-DA database is planned in the frame of the EVRS, and occasional upgrades may be published when significant new input data become available.
The EUVN-DA final report (EUVN-DA final report (PDF, 2MB)) gives a general overview and summarizes the results achieved.
EUVN as starting point
The final product of the EUVN project was an open database, where all benchmarks were associated with cm-accuracy 3D coordinates in ETRS89 (ETRF96 epoch 1997.4) and geopotential numbers related to EVRS2000 zero level, which were used to derive normal heights. Detailed description of the project and the results can be found in (Ihde et al, 2000). To get an independent measure of quality the authors compared the available ellipsoidal and normal heights with the EGG97 continental quasigeoid solution. Generally, the EGG97 and EUVN height anomalies agreed within 2 dm (see Figure1), where some points are suspected as outlier. There are regions (Alps, South-East-Europe, Baltic, Central Scandinavia, Atlantic coastline), where systematic, large scale trends and / or biases are clearly observable. As EUVN is a sparse network the modeling and separation of the large scale biases was hardly possible. The general conclusion was that a more accurate continental geoid solution and a denser GPS / levelling network is required.
In 2003 the former IAG European Subcommission IGGC (International Gravity and Geoid Commission) in cooperation with EUREF initiated the EUVN densification project. A parallel development was started targeting the establishment of a homogeneous, cm-accuracy continental GPS / levelling database and a new improved European quasigeoid solution.
The main task of EUVN-DA is the creation and maintenance of an accurate standardized, dense continental GPS / levelling database. EUREF closely cooperates with EGGP in the creation of an accurate continental height reference surface, consistent with ETRS89 and the EVRS. EUVN-DA not considered as a direct continuation of the EUVN project. The EUVN-DA activities are more practice-oriented, the tasks, already successfully completed in EUVN (levelling network connections, height datum establishment, tide gauge investigations) are out of scope.
Due to the expected large number EUVN-DA benchmarks (over 1200 points) a coordinated GPS campaign was not feasible due to financial and logistical constrains. Each participating country was asked to establish the national contribution independently, along pre-defined quality standards. Existing GPS / levelling data, corresponding to the standards was also accepted.
Although the established set of quality measures would allow to achive the 1 cm accuracy both for the GPS and levelling data on the local level, the full homogeneity for the whole network cannot be reached, due to the variable reference epochs of the measurements. The Nordic countries are exceptional, they agreed on a commonly accepted Land Uplift model (NKG2005LU), which is used to transform the measurements performed in different epochs to epoch 2000.0.
The homogeneity of the levelling data - in terms of reference frame - was ensured, as most of the EUVN-DA benchmarks are connected to a nearest UELN marker. Such EUVN-DA points are becoming part of UELN and they will be included into the future UELN adjustments.
Related EUREF Resolutions
Resolution No. 3
of the EUREF Symposium in Tromsø 22 –24 June 2000
The IAG Subcommission for Europe (EUREF)
noting Resolution No.3 of the EUREF Symposium 1998 in Bad Neuenahr-Ahrweiler,
recognizing the completion of the EUVN height solution, which includes GPS / levelling geoid heights,
thanks the National Mapping Agencies for their support in supplying data,
recommends that the GPS / levelling heights of the EUVN solution should be used as fiducial control for the future European geoid determinations,
asks the relevant authorities
- to provide the necessary information for tide gauge connections,
- to densify the network of EUVN GPS / levelling geoid heights,
to complete and extend the EUVN project.
Resolution No. 4
of the EUREF Symposium in Dubrovnik, 16-18 May 2001
The IAG Subcommission for Europe (EUREF)
- the European Vertical Reference Network (EUVN) with its GPS-derived ellipsoidal heights and leveled connections to UELN,
- the definition of the European Vertical Reference System EVRS with its first realization UELN 95/98, called EVRF2000,
- this implicit pointwise realization of a European geoid consistent with both ETRS89 and EVRS,
- the existence of a large number of regional and local geoids in Europe,
- the urgent need by the navigation community for a height reference surface,
its Technical Working Group and the European Subcommission of the IAG IGGC (International Gravity and Geoid Commission) to take all necessary steps to generate a European geoid model of decimetre accuracy consistent with ETRS89 and EVRS.
Resolution No. 4
of the EUREF Symposium in Florence, 16-18 May 2009
The IAG Reference Frame Sub-commission for Europe (EUREF)
- the advantage of combining gravity field parameters with geometric observations to stabilize geodetic reference systems
- the availability of the new realisation of the European Vertical Reference System EVRF2007 and the advanced status of the EUVN-DA project
- and the continuation of the EUREF project "European Combined Geodetic Network" (ECGN)
asks the TWG to contact the European Geoid Project in order to develop a combined European geoid to link ETRS89 and the EVRS.