Gravitacijos lauko parametrų Lietuvoje tikslinimas

Abstract

Navigacijos uždavinių sprendimus, oro uostų geodeziniam aprūpinimui pagal ICAO ir kitų tarptautinių organizacijų reikalavimus būtina informacija apie Žemės gravitacijos lauką. Šį lauką charakterizuojantys parametrai - sunkio jėgos pagreitis, geopotencialo koeficientai, geoido aukščiai elipsoidiniu atžvilgiu ir kt. gali būti nustatyti klasikinės ir kosminės geodezijos metodais. VGTU Geodezijos institutas tiria gravitacijos lauką ir geoidą nusakančius parametrus Lietuvos teritorijoje. Absoliučios sunkio jėgos pagreičio tyrimuose balistiniu metodu Vilniuje, Panevėžyje, Klaipėdoje buvo pasiektas 5-7 μgal tikslumas.Taip pat 60-je gravitacijos lauko taškų sunkio jėgos pagreičiui atlikti preciziniai matavimai. Šių matavimų pagrindu ir panaudojus dar GPS matavimus, buvo suskaičiuotas geoido modelis Lietuvos teritorijai. Dabar geoido aukščiai virš elipsoido yra žinomi 2 - 3 cm tikslumu. Tai įgalina tolesnius didelio tikslumo matavimus aukščių ir nelygumų nustatymui oro uostuose ir kituose uždaviniuose.

Solutions of the navigational tasks and airports geodetic maintenance according to requirements of ICAO and other international organizations need information about the Earth gravity field. The parameters of the gravity field as a gravity force acceleration, geopotencial coefficients, geoid heights above ellipsoid and others could be defined by ordinary and satellite gravimetric and geodetic measurements. Global gravity models and detail gravimetric maps were constructed on the base of such measurements. They are used in geophysical, geodetic and navigational investigations. The measurements of gravity force acceleration were performed in Lithuania, too. Gravimetric networks were developed twenty years ago and, certainly, do not fit to the nowadays requirements. The same problem exists in the defining of the geoid surface. VGTU Geodetic institute investigates the gravity field and geoid determination in Lithuania territory. In 1994 with a help of Finnish Geodetic Institute the observations of absolute gravity force accelerations by ballistic method were performed in three points (Vilnius, Panevėžys, Klaipėda). Accuracy of 5 - 7 μgal was achieved. These points are the excellent base for the development of Lithuania state gravity network. In 1998 according to cooperation agreement between Danish and Lithuanian specialists the gravity network of 60 sites was observed. Measurements were performed by two precise gravimeters La Coste & Romberg. The standard deviations of gravity force accelerations at the sites are not bigger than 17 μgal. Such precise measurements of gravity force accelerations were performed in the GPS stations of Vilnius, Šiauliai and Karmėlava airports. On the base of new gravity and GPS measurements the geoid model of Lithuania territory was calculated. The geoid heights above ellipsoid are known with an accuracy of 2 - 3 cm. The modern geoid model enables to use the GPS method for deriving the ellipsoidal and normal heights and to solve other geodetic tasks in airports with an accuracy according to requirements of ICAO and other international organizations.