Quality of Lithuanian national gravimetric network

Abstract

In 1994 the absolute gravity measurements were carried out by J. Mäkinen (Finish Geodetic Institute) at three stations of Lithuania. Measurements were performed by ballistic gravimeter JILAg-5. Absolute gravity measurements were repeated in 2002. The 5 µGal precision of the gravity acceleration was derived. The differences between the gravity acceleration values, obtained in 1994 and 2002 fall into the limits of the accuracy of measurements. These three stations form the National zero order gravimetric network – the basis of the new gravity system and further densification of the gravimetric network. From 1998 to 2001 the National first order gravimetric network was observed. There are 51 gravimetric points in the National first order gravimetric network, evenly distributed in the territory of country. Measurements were carried out by LaCoster & Romberg gravimeters. Each gravity difference of the network was measured at least three times with 3 or even 6 gravimeters. Accuracy of adjusted gravity acceleration values of 3–4 µGal was received, and the standard deviation of the single gravity difference observation of 14 µGal was derived. In July of 2006 some points were re-observed by 2 pairs of SCINTREX CG-5 gravimeters. Accuracy of adjusted gravity acceleration values of 3–7 µGal was received, and the standard deviation of the single gravity difference observation of 17 µGal was derived. Comparison of computed gravity acceleration values shows, that differences are bigger, than it was expected. It can be concluded that further studies of the stability of the gravimeters performance and the uncertainties in relative measurements is still required.