This paper considers the origin of Latvian Coordinate System LKS-92 definition which was based on two GNSS campaigns in 1992 and 2003. There are two continuously operating reference networks in Latvia: LatPos and EUPOS ®-Riga. GNSS stations of these networks have fixed coordinate values in LKS-92. At the Institute of Geodesy and Geoinformatics of the University of Latvia both LatPos and EUPOS ®-Riga station daily coordinate values are calculated. The coordinate differences between epochs 1989.0 and 2018.5 were obtained for LatPos and EUPOS ®-Riga stations, expressed in ITRF14. ITRF reflects the motion of Eurasian plate in global frame of the Earth and ETRF89 system reflects the intraplate motion. Mean yearly coordinate components in ETRF89 were analysed. Comparison of LatPos and EUPOS ®-Riga station coordinate components in ETRF89, LKS-92 and ETRF2000 coordinate systems was performed. Future of Latvian coordinate system LKS-92 is discussed.

Abstract. The GPS observations of both Latvian permanent GNSS networks -EUPOS® -Riga and LatPos, have been collected for a period of 8 years -from 2007 to 2014. Local surface displacements have been derived from the obtained coordinate time series eliminating different impact sources. The Bernese software is used for data processing. The EUREF Permanent Network (EPN) stations in the surroundings of Latvia are selected as fiducial stations. The results have shown a positive tendency of vertical displacements in the western part of Latviastation heights are increasing, and negative velocities are observed in the central and eastern parts. Station vertical velocities are ranging in diapason of 4 mm/year. In the case of horizontal displacements, site velocities are up to 1 mm/year and mostly oriented to the south. The comparison of the obtained results with data from the deformation model NKG_RF03vel has been made. Additionally, the purpose of this study is to analyse GPS time series obtained using two different data processing strategies: Precise Point Positioning (PPP) and estimation of station coordinates relatively to the positions of fiducial stations also known as Differential GNSS.

Abstract. The objective of this paper is to analyse water level variations of the Baltic Sea on the Latvian coast. This is important because the Baltic Sea exhibits a number of remarkable phenomena. One of them is the sea level variations due to winds, complicated by the shape of the gulfs and islands. Under this influence the range of the sea level variations can reach 3 m on the coasts of gulfs. However, the tidal variations of the Baltic Sea range in the order of centimetres only. In the frame of this study, using hourly time series of the sea level records from 7 Latvian coastal hydrologic stations and employing spectral analysis, it has become feasible to identify diurnal and semi-diurnal tide existence both in the Gulf of Riga and in the Baltic Sea at the Latvian coast. Totally 4 main tidal constituents (O 1 , K 1 , M 2 , S 2 ) have been identified. Additionally, nontidal frequency of 5 cycles per day has been detected in the sea level time series of the stations located in the Gulf of Riga.

The determination of parameters for identifying stars sensed by charge-coupled device (CCD) is discussed. Numerical experiments are summarized which support the parameter space bound estimation practicality of the proposed star pattern recognition and identification by matching with coordinate list in star catalogue. The parameter analysis performed to apply them for proper identification algorithm which is developed and used at the Institute of Geodesy and Geoinformatics. This algorithm is applied for identification of large volume star sets.