Europos vertikaliojo tinklo plėtimas Lietuvos teritorijoje

Abstract

Within the frame of the IAG-Subcommision for Europe (EUREF) the activities of the European Vertical GPS-Reference Network (EUVN) have been carried out on the basis of Resolution No 2 of the EUREF Symposium in Helsinki, May 1995 and Resolution No 3 of the EUREF Symposium in Ankara, May 1996. The EUVN is designed to contribute to the unification of different height systems in Europe. The final objective of the EUVN is to provide a set of coordinates for all EUVN sites consisting of three-dimentional coordinates X, Y, Z , respective latitude, longitude, ellipsoidal height and the “physical” height derived from levelling and gravity measurements win respect of the UELN and/or UPLN and/or of the national height systems. The most important practical and scientific aspects are contribution to a unique European height datum, connection of European tide gauge benchmarks as the contribution to monitoring absolute sea level variation, establishing of fiducial points for the European geoid determination, preparation of a European Vertical Kinematic Network. Lithuanian geodesists hope that realisation of the EUVN project will be a background for adopting and developing the vertical reference of Lithuania. Three sites of EUVN are in Lithuanian territory: Vilnius (LT02), Šiauliai (LT01) and Molas (LT03). All of them were connected to the nearest nodal points of united Precise Levelling Network (UPLN) in summer of 1997. The GPS observations were carried out in the period from May 21 to May 29, 1997. The Ashtech Z12 receivers were used, the time interval was set to 30 seconds, the cut-off angle was 5°. The Baltic Sea Level (BSL) GPS campaign was done simultaneously with the EUVN because most of the points were common in surroundings of the Baltic Sea. Two points are in the BSL GPS network: Molas and Klaipeda. Authors would like to thank Prof. Kai Borre, Aalborg University, and Dr. Jan M. Johansson (Onsala Space Observatory) for providing necessary GPS receivers.