No abstract

Gravity anomalies provide valuable information about the Earth‘s gravity field. They are used for solving various geophysical and geodetic tasks, mineral and oil exploration, geoid and quasi-geoid determination, geodynamic processes of Earth, determination of the orbits of various objects, moving in space around the Earth etc. The increasing accuracy of solving the above mentioned problems poses new requirements for the accuracy of the gravity anomalies. Increasing the accuracy of gravity anomalies can be achieved by gaining the accuracy of the gravimetric and geodetic measurements, and by improving the methodology of the anomalies detection. The modern gravimetric devices allow to measure the gravity with an accuracy of several microgals. Space geodetic systems allow to define the geodetic coordinates and ellipsoidal heights of gravimetric points within a centimeter accuracy. This opens up the new opportunities to calculate in practice both hybrid and pure gravity anomalies and to improve their accuracy. In this context, it is important to analyse the possibilities of detecting various gravity anomalies and to improve the methodology for detecting gravity anomalies. Also it is important the correct selection of the gravity anomalies for different geodetic, geophysical and environmental engineering tasks. The modern gravity field data of the territory of Lithuania are used for the research.

Sunkio laukui nustatyti Lietuvos teritorijoje svarbu turėti didelio tikslumo ir tankumo gravimetrinius duomenis. Siekiant sumodeliuoti gravitacijos lauką teritorijoje, būtina įtraukti ir ežeringas teritorijas. Dideli ežerai, marios ar kiti didelio ploto vandens telkiniai visada buvo problema regioninėms sunkio lauko duomenų bazėms. Didžiausių sunkumų kyla dėl duomenų tuštumų ar per didelio atstumo tarp matuojamųjų punktų. Palydovinė, skrydžio ar laivais atliekami gra-vimetriniai matavimai taikomi jūrų, vandenynų sunkio laukui nustatyti, tačiau ežerų ar kitų regioninių vandens telkinių gravimetriniams matavimas jie yra nepraktiški dėl savo kainos ar skiriamosios gebos (tikslumo). Šiame straipsnyje anali-zuojamas antžeminis sunkio lauko nustatymo metodas ant užšalusio ežero, kuriame ledas juda dėl vėjuotų sąlygų. Per pastaruosius trejus metus Lietuvoje buvo atliktos kelios gravimetrinių matavimų kampanijos ant ledu padengtų ežerų, marių ir tvenkinių. Šių matavimų užduotis – užpildyti sunkio lauko duomenų spragas Lietuvos teritorijoje. Aliekant mata-vimus buvo stebėtas vėjo greitis matavimų metu, įvertintas ledo storis, vandens gylis ir specialia įranga stebėtas ledo vib-ravimas. Daugybė veiksnių turi įtakos gravimetriniams matavimams ant ledu padengtų vandens telkinių, Juos būtina kuo tiksliau įvertinti, eliminuoti matavimų klaidas, sudaryti tikslesnių gravimetrinių matavimų metodiką.

New research of Lithuanian territory gravity field was started in 2016 with aim to improve accuracy of quasigeoid as well as accuracy of normal heights determined by methods of satellite geodesy. Obtained data could be used in the research of geophysics, geodynamics as well as in performing the precise navigation. Quartz automatic gravimeters Scintrex CG-5 are planned to be used for the survey consisting of 30000 points. Method of gravity measurements was worked out. RMS error of gravity determined with this method does not exceed 60 @Gal. Coordinates and heights of measured points are determined with GNSS using LitPOS network and LIT15G quasigeoid model. RMS error of coordinate determination does not exceed 0,20 m, for normal heights – 0,15 m. Method of gravity anomalies determination and their accuracy estimation was prepared.

Abstract. Lithuania is successfully integrated in the European geomagnetic field research activities. Six secular variation research stations were established in 1999 and precise geomagnetic field measurements were performed there in 1999, 2001, 2004, 2007 and 2016. Obtained diurnal magnetic field variations at measuring station and neighbouring observatories were analysed. All measurements are reduced to the mean of the year using data from geomagnetic observatory of Belsk. Based on the measured data the analysis of geomagnetic field parameter secular changes was performed. Results of the presented research are useful for updating the old geomagnetic data as well as for estimation of accuracy of declination model.