Lietuvos valstybinio gravimetrinio nulinės klasės tinklo sudarymas

Abstract

The establishment of Lithuanian National Zero Order Gravity Network by observing absolute gravity force on sites is described. A review of gravity observations in Lithuania is provided. It was proved that present gravity control network accuracy does not fit to nowadays requirements. Reference points of extra accurate absolute gravity observations are needed to establish a modern gravity network. Such observations after suggestion of prof. J.Kakkuri have been performed by Finnish Geodetic Institute. Technical conditions of gravity points establishment have been analysed. Mark of gravity point have been designed. Points have been established in the celars of buildings in Klaipėda, Panevėžys and Vilnius. Sites for the points have been selected under the consultance of Finnish experts as well as correlating with State Department for Surveying and Mapping, and State Service of Geology. Drills for ground water level observations have been established in the suroundings of points in Klaipėda and Vilnius. Altitudes of these points have been determined by precise levelling from first and second order leveling bench marks, in Baltic height system of 1977. Level Ni002 have been used. These activities have been performed by specialists of Institute of Geodesy, VTU. Method of balistic absolute gravity measurements, main sources of errors, instrument used (JILAg-5) have been described in short. Absolute gravity observations at points of Klaipėda, Panevėžys and Vilnius have been performed at July 14th - August 1st, 1994. Observations and data processing were carried on by Jaakko Makinen, specialist of Finnish Geodetic Institute. Performed absolute gravity observations are creating a base for future gravimetric activities in Lithuania.