No abstract

Activities of Lithuanian National Geodetic Vertical Reference Network (NGVRN) establishment are going on since 1998. The goal of NGVRN establishment is a creation of new Lithuanian height reference suitable for present period practical and scientific needs. The Lithuanian Geodetic Vertical First Order Network consists of five polygons. Perimeter of the network is ca. 1900 km. Its development was finished in 2006. Connections of the first order vertical network with the vertical networks of neighbouring countries were established. All this creates good preconditions for determination of relations between height systems and for introduction of a new Lithuanian geodetic vertical (height) system. But this network is not dense enough to transfer the geodetic vertical system to the all territory of Lithuania and to improve the geoid model. It is necessary to dense available First Order Geodetic Vertical Network by developing the Second Order Geodetic Vertical Network. The territory of Lithuania is divided into five regions. Borders of the regions are First Order Network levelling lines and lines connecting Lithuanian national Vertical Network to the corresponding networks of the neighbouring countries. The regions are called: South, East, North, West and Centre. The design of the Second Order Geodetic Vertical Network is presented. The necessary density, accuracy of the geopotential numbers and ellipsoidal heights are discussed. Some results of the geodetic measurements are presented too.

The laboratory and field investigations of the several automatic gravimeters Scintrex CG_5 with a quartz elastic system used for the determining of gravity acceleration were performed. Research on characteristics of four gravimeters includes a five-year period. The data consists of gravimetric observations at a laboratory, on the gravimetric testline and at the points of the Lithuanian gravimetric network. The evaluation of the phenomena of the spring systems of the gravimeters was made. The stress on the estimation of the zero drift at a laboratory and field investigations was done. It was detected that zero drift does not exceed 500 μGal per day with a diapason of 200 μGal. The zero drifts per hour do not exceed 25 μGal, mostly they are under 10 μGal. According to the annual calibration results the character of the changes of the linear scale coefficients of the gravimeters were analysed too. The calibration base of 270 km length in Lithuania where the difference of the gravity acceleration of the end points is 201 mGal was used for investigations. The research showed that the biggest deviation from the unit of the linear scale coefficients does not exceed 0.013. It was noted, that the values of the linear scale coefficients of the gravimeters have a tendency to decrease. Also was noted, that the values of the linear scale coefficients have a tendency to decrease in the period between field works, and to increase - in the field works period. So the calibration of the gravimeters should be carried out before and after the field works. Based on measurements carried out during development of the Lithuanian gravimetric network, which consists of 686 gravimetric points, accuracy of gravity acceleration increments was assessed. The comparison of the observations results against the results, obtained by the LaCoste and Romberg gravimeters with metal elastic system, is presented too. The total number of common points is 51. It was stated, that the differences of the gravity accelerations measured by the different types of gravimeters at gravimetric points do not differ more than 10 μGal, therefore maximum difference of 25 μGal was received. The standard deviations of the gravity accelerations of the gravimetric points do not exceed 7 μGal. Such results show the good performance of the SCINTREX CG_5 gravimeters.

No abstract

The authors of the paper present analysis of the baseline calibration results that they have performed. The Kyvišk_ es Calibration Baseline (1320 m) is the longest calibration baseline in Lithuania.