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Tallinn, Estonia

Oja T.,Estonian Land Board
International Association of Geodesy Symposia | Year: 2012

Preparations to establish a new accurate gravity network in Estonia were initiated in 2001. Since then several LCR (LaCoste&Romberg) G-type and Scintrex CG-5 relative gravimeters have been used to determine gravity differences precisely. The calibration functions of those relative instruments have been repeatedly checked at the calibration lines in Estonia and in Finland. Since the beginning of the 1990s absolute gravity values have been determined three times in Estonia: in 1995 at three stations with JILAg-5 by the Finnish Geodetic Institute (FGI), in 2007 at two stations with FG5-220 by the Institut für Erdmessung (IfE), University of Hannover, and a year later at seven stations with FG5-221 again by FGI. On the ground of collected absolute and relative gravity data, a new realization (network GV-EST) of the Estonian gravity system (EGS) is currently being established. However, before the completion of the network, several issues should be solved, including the calibration of relative gravimeters, the corrections of readings and setup of the functional model, the weighting of observation data and selection of statistical tests, the short and long term changes of the gravity field, the choice of the epoch. In the current paper I introduced the concept of EGS as well as the methodology to solve the afore-mentioned issues. Since the estimated uncertainties of gravity values from network adjustment stayed below ±10 μGal (1 μGal = 10-8 m/s2) it was concluded that the selected methods had been efficient. © Springer-Verlag Berlin Heidelberg 2012.

Turk K.,Estonian University of Life Sciences | Sulaoja M.,Estonian University of Life Sciences | Oja T.,Estonian Land Board | Ellmann A.,Tallinn University of Technology | Jurgenson H.,Estonian University of Life Sciences
8th International Conference on Environmental Engineering, ICEE 2011 | Year: 2011

In 2009 and 2010 two gravity campaigns were carried out in Southeast Estonia. A relative La-Coste&Romberg (LCR) gravimeter in combination with RTK GPS/GNSS positioning device were used for determining gravity values and positioning of the survey sites. The points of modern national gravity network were taken as initial for measurements. Altogether 344 new points were observed during the field campaigns, the achieved accuracy varied from ±0.07 to ±0.1 mGal. The survey points were mainly located alongside roads, whereas the distance between neighboring survey points varied from 3 to 5 km. Crossroads and other prominent sites as well as national geodetic network points were chosen as preferred survey locations. The results were compared with two existing gravity databases: (i) the database of the Estonian Geological Survey and, (ii) a historic dataset obtained in 1949⋯ 1958. The comparison included matching the measured Bouguer gravity anomalies with predicted Bouguer anomalies (using the existing datasets) at the locations of the new survey sites. The discrepancies between the new and historic datasets up to ±3.5 mGal with standard deviation 0.9 mGal of were detected. A better match was found from the comparison with the Estonian Geological Survey dataset (biases ± 0.2 mGal). The purpose for new campaigns was to replace older systematically biased gravity data with new accurate survey points. © Vilnius Gediminas Technical University, 2011.

Motlep R.,University of Tartu | Sild T.,Estonian Land Board | Puura E.,University of Tartu | Kirsimae K.,University of Tartu
Journal of Hazardous Materials | Year: 2010

Oil shale is a primary fuel in the Estonian energy sector. After combustion 45-48% of the oil shale is left over as ash, producing about 5-7. Mt of ash, which is deposited on ash plateaus annually almost without any reuse. This study focuses on oil shale ash plateau sediment mineralogy, its hydration and diagenetic transformations, a study that has not been addressed. Oil shale ash wastes are considered as the biggest pollution sources in Estonia and thus determining the composition and properties of oil shale ash sediment are important to assess its environmental implications and also its possible reusability.A study of fresh ash and drillcore samples from ash plateau sediment was conducted by X-ray diffractometry and scanning electron microscopy. The oil shale is highly calcareous, and the ash that remains after combustion is derived from the decomposition of carbonate minerals. It is rich in lime and anhydrite that are unstable phases under hydrous conditions. These processes and the diagenetic alteration of other phases determine the composition of the plateau sediment. Dominant phases in the ash are hydration and associated transformation products: calcite, ettringite, portlandite and hydrocalumite. The prevailing mineral phases (portlandite, ettringite) cause highly alkaline leachates, pH 12-13. Neutralization of these leachates under natural conditions, by rainwater leaching/neutralization and slow transformation (e.g. carbonation) of the aforementioned unstable phases into more stable forms, takes, at best, hundreds or even hundreds of thousands of years. © 2010 Elsevier B.V.

Vain A.,Estonian Land Board | Vain A.,Estonian University of Life Sciences | Liba N.,Estonian University of Life Sciences | Sepp K.,Estonian University of Life Sciences
8th International Conference on Environmental Engineering, ICEE 2011 | Year: 2011

Airborne laser scanning (ALS) intensity data is a source of additional information describing the backscat-tering properties of the observed object. But there are several factors that affect the intensity values. This article describes these factors and their influence on the final results. Because the laser beam travels through atmosphere and back, it attenuates due to the different atmospheric conditions. The pulse energy level difference is another important factor that has to be considered when we want to compare the intensity data. Since there is not enough information about the energy levels that are used, it has been difficult to correct it. But the manufactures have understood the importance of that additional information and newer ALS systems already record the transmitted energy levels. The range and the incidence angle (angle between surface normal and incoming laser beam) is also affecting the final intensity data. This paper will also discuss the feature called Automatic Gain Control (AGC) that is used in Leica ALS50-II scanner and is also affecting the intensity values. © Vilnius Gediminas Technical University, 2011.

Plado J.,University of Tartu | Sibul I.,Estonian Land Board | Mustasaar M.,University of Tartu | Joeleht A.,University of Tartu
Estonian Journal of Earth Sciences | Year: 2011

The current case study presents results of the ground-penetrating radar (GPR) profiling at one of the Saadjärve drumlin field interstitial troughs, the Rahivere bog, eastern Estonia. The study was conducted in order to identify the bog morphology, and the thickness and geometry of the peat body. The method was also used to describe the applicability of GPR in the evaluation of the peat deposit reserve as the Rahivere bog belongs among the officially registered peat reserves. Fourteen GPR profiles, ~ 100 m apart and oriented perpendicular to the long axis of the depression, covering the bog and its surrounding areas, were acquired. In order to verify the radar image interpretation as well as to evaluate the velocity of electromagnetic waves in peat, a common source configuration was utilized and thirteen boreholes were drilled on the GPR profiles. A mean value of 0.036 m ns-1 corresponding to relative dielectric permittivity of 69.7 was used for the time-depth conversion. Radar images reveal major reflection from the peat-soil interface up to a depth of about 4 m, whereas drillings showed a maximum thickness of 4.5 m of peat. Minor reflections appear from the upper peat and mineral soil. According to the borehole data, undecomposed peat is underlain by decomposed one, but identifying them by GPR is complicated. Mineral soil consists of glaciolimnic silty sand in theperipheral areas of the trough, overlain by limnic clay in the central part. The calculated peat volumes (1 200 000 m3) were found to exceed the earlier estimation (979 000 m3) that was based solely on drilling data. Ground-penetrating radar, as a method that allows mapping horizontal continuity of the sub-peat interface in a non-destructive way, was found to provide detailed information for evaluating peat depth and extent.

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