Common Studies of National Height System in Latvia and Lithuania

Abstract

Already after our independence in the nineties of the twentieth century, we used common height system-Baltic Normal height system 1977 (BHS 1977). Latter we have made big job for verification and modernization of our geodetic network in the frames of different international campaigns. There we always cooperating with Nordic countries in frames of Nordic Geodetic Commission (NKG). Also we have had sector programme between Denmark and Baltic countries about modernization of geodetic network. Already in that time we carried out common work in the field of gravity survey, levelling and GNSS observation. As European Union member states-Latvia and Lithuania have changed their national height systems to European Vertical Reference System realizations. Latest product of such efforts, we have freely available latest Nordic quasi-geoid model NKG2015, too. For studies of height network consistency in regional and international level we carry out GNSS observation campaigns and making comparison of the obtained survey results and computed ones from different geoid models, for example LV98, NKG2015, EGG2015 etc. In such way, we are making conclusions about quality of geodetic network and giving recommendation for the future work. The aim of the research is using GNSS measurements gain insight for methodology development of geodetic point height testing. To achieve the aim following tasks were set: 1) perform GNSS measurements of first order levelling network points in Latvia and Lithuania; 2) to do data processing to get station coordinates; 3) to compare point elevations. For GNSS measurements use for height determination it is very significantly to use advanced measuring technologies and verified data processing methodology. RMS errors describe high accuracy of performed measurements.