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Gravimetric Network

Gravity frame EG2000

The Estonian gravity frame EG2000 assures accurate gravity values throughout the country. The nationwide network is divided into I, II and III order points according to the stability, accessibility of the point and the accuracy of the gravity value determined on the point.

The gravity frame is fixed by absolute gravity determinations at seven I order points by using free-fall JILAg and contemporary FG5 absolute gravimeters. The uncertainty of gravity at I order points is equal or better than 100 nm/s². Hundreds of II and III order points have been connected to the I order network by applying relative LCR G and Scintrex CG5 gravimeters. The scale of relative gravimeters has been checked along a special gravity calibration line connecting absolute gravity sites. Observation data were processed according to the International Absolute Gravimeter Basestation Network (IAGBN) standards. The epoch 2000 has been used to reduce the postglacial rebound effect on gravity.

Figure 1. Estonian gravity network to maintain the national gravity reference frame EG2000. Absolute gravimeters have been used to determine gravity at I order points which have been connected to the II and III order points by using relative gravimeters (blue and red lines, respectively).

Gravity anomaly model

The historic (1949-1991) and new (1992-2017) gravity data, altogether about 144 000 gravity survey points, were used to compute the residual terrain model anomalies (RTMA). Based on the RTMA values of gravity points the grid surface model was compiled by using geostatistical prediction method (the least squares collocation). The RTMA surface model can easily be converted to the free-air, Bouguer anomaly models, or the gravity model on land and water surfaces (Fig. 2).

The gravity data from neighbouring countries (Finland, Latvia, Lithuania and Sweden) were obtained through international cooperation in the working groups of the Nordic Geodetic Commission (NKG). The new marine gravity data were acquired from the international FAMOS (Finalising Surveys for the Baltic Motorways of the Sea) project.

Figure 2. The gravity acceleration on land and water surfaces within the Estonian land and maritime borders derived from the gravity anomaly (RTMA) model. The mean value of gravity is 9.81796 m/s² (981796 mGal) and the change from south to north is about 0.0022 m/s² (220 mGal).

Contact

Karin Kollo


Last update: 02.12.2019 15:17
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