Reference frame densifications for Nordic and Baltic countries - From local analysis to common and consistent GNSS solutions

Sonja Lahtinen

Research output: ThesisDoctoral ThesisCollection of Articles


Terrestrial, Earth-fixed, reference frames are fundamental, but often unnoticeable, components for modern societies. Today, regional terrestrial reference frames are created and maintained by the measurement of continuously operating Global Navigation Satellite System (GNSS) reference stations. In Fennoscandia, glacial isostatic adjustment (GIA) causes deformation, also known as postglacial rebound, decreasing the accuracy of national static reference frames referring to the European Terrestrial Reference System 1989 (ETRS89). Considering the deformation is thus a necessity to accurately transform coordinates from the International Terrestrial Reference Frame (ITRF) to national ETRS89 realisations such as EUREF-FIN in Finland. This dissertation focused on estimating densified reference frame realisations in the global reference frames for the Nordic and Baltic countries. The work was carried out in the GNSS Analysis Centre project of the Nordic Geodetic Commission (NKG). It builds on eight local analysis centres, one in each country, processing its sub-net. The emphasis of the dissertation was on developing methods for combination of the sub-nets, analysis of the time series, and estimating a multi-year position and velocity solution, including uncertainties of the station velocities. The results showed that the sub-net solutions were consistent with the combined solution within 1–2 mm. The distribution of the GNSS processing into local sub-nets thus strengthened the daily solutions due to the redundantly processed reference stations. The station-wise position time series were analysed for offsets both manually and with the developed automatic approach with a 74 % success rate in respect to the manual interpretation. Station velocities were estimated for approximately 270 stations from daily position solutions. The lengths of time series varied between 3 and 20 years. Uncertainty levels of 0.10, 0.10, and 0.25 mm/y for the north, east, and up components respectively were reached with 10 years of data for more than 90 % of stations. The detailed understanding of the GNSS time series in the Nordic and Baltic countries will enhance the quality of the European and global terrestrial reference frame realisations, because some of the stations contribute with the same data to those solutions. The densified reference frame solutions will be utilised in the maintenance of the national geodetic reference frames, including deformation modelling and the development of the accurate coordinate transformations. This will ultimately extend the lifetime of the national reference frames like EUREF-FIN.
Translated title of the contributionVertauskehysten tihennyksiä Pohjoismaiden ja Baltian alueelle
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Nordman, Maaria, Supervising Professor
  • Koivula, Hannu, Thesis Advisor
Print ISBNs978-952-64-0770-8, 978-951-48-0280-5
Electronic ISBNs978-952-64-0771-5, 978-951-48-0279-9
Publication statusPublished - 2022
MoE publication typeG5 Doctoral dissertation (article)


  • GNSS
  • terrestrial reference frames
  • GNSS time series
  • GNSS velocities
  • ITRF


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