Lietuvos gravimetrinio pagrindo tyrimas ir tobulinimas

Abstract

In this article the results of the analysis of the accuracy of the present Lithuanian gravity control are presented and recommendations for its rational development are given. A historical review of gravity observations in Lithuania is provided. It was proved that the present gravity control network accuracy does not meet nowadays requirements and that a new modem gravity network should be developed. The results of the gravity measurements in 1998 are presented and analysed. The network consists of 64 gravity points. The stations are often chosen in churches or other official buildings close to the motorway system, in order to combine lasting existence with easy access and quick transport. The gravity network is based on LaCoste&Romberg relative gravity observations, constrained by absolute gravity values. The raw gravimeter observations were converted into 'reduced readings’ by the GRREDU software prior to adjustment of the network. The gravity observations in the Lithuanian precision gravity network have been adjusted by least squares method based on reduced gravimeter readings and the adopted absolute gravity values. The adjustment has been done by the GRADJ software from the GRAVSOFT software package for physical geodesy. In the final adjustment of the 384 observations in 64 stations, a posteriori standard deviation of a single reading was estimated as 0.017 mGal. It appears that the absolute values agree very well with the relative observations, and the general accuracy level of the adjusted gravity values of network points is in the range of 7-13 µGal. The gravity measurements were used for analysing the accuracy of the gravity map of 1952-62 and the second order gravity network. The differences between gravity force accelarations were calculated. The biggest difference is :+2.159 mGal (station DRUSKININKAI 1070) and -1.746 mGal (station STULGIAI), and average value is 0.084 mGal. The standard deviation of the gravity force acceleration obtained from gravity maps is 0.68 mGal. On the basis of the presented investigations the Lithuanian First order gravity network was designed. The accuracy of its elements will be in the range of few µGal.