Some issues of the national gravimetric network development in Lithuania

The gravity height systems adoption is crucial in development of national geodetic reference. Successful solution of this questions guarantees the reliable determination of geopotential heights, usage of modern geodetic space techniques, maintenance of the navigation, geodetic and cartographic works, solution of geodynamic tasks, support the relations between the similar systems of other countries, participation in the international projects. The gravity and height systems should be related with the geocentric geodetic coordinate system. In Lithuania such a system was adopted in 1994 as a Lithuanian Coordinate System (LKS 94). It is consist with European Terrestrial Reference System 1989 (ETRS 89). With adoption of LKS 94 the normal gravity field GRS 80 was introduced. It was recommend by the International Association of Geodesy (IAG). To introduce the new gravity system instead of Potsdam system the absolute gravity measurements were carried out in 1994. Such measurements were carried out by Jaakko Makinen (Finish Geodetic Institute). Measurements were performed by ballistic gravimeter JILAg-5 in the points VILNIUS, KLAIPEDA and PANEVEZYS. Absolute gravity measurements were repeated in 2002. The 5 µGal precision of the gravity acceleration was derived. Some issues of development of the National gravimetric network are discussed. The main stress is given to the analysis of the precision of the gravity acceleration at the points of the gravimetric network. The calibration of the gravimeters was carried out before and after field survey. The difference of the gravity acceleration of the calibration bases is 202 mGal, and two zero order and two first order points are in it. The standard deviation of the linear scale coefficients of 0.00006 was received. The maximal change of the linear scale coefficients during all time of field campaign was 0.000159 (gravimeter No 183). During the three months of period of investigations the zero drift of the gravimeters was changed from 17 till 197 µGal/day. The National gravimetric network was adjusted using software package GRAVSOFT. Total number of observations is 33777. The three absolute gravity stations were chosen as initial points. Standard deviation of the single observation equal to 5 µGal, and standard deviation of gravity acceleration of the single points equal to 3 µGal were received