Estonian Land Board

Tallinn, Estonia

Estonian Land Board

Tallinn, Estonia
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Mardla S.,Tallinn University of Technology | Agren J.,Lantmateriet | Strykowski G.,Technical University of Denmark | Oja T.,Estonian Land Board | And 7 more authors.
Marine Geodesy | Year: 2017

The deduction of a regularly spaced gravity anomaly grid from scattered survey data is studied, addressing mainly two aspects: reduction of gravity to anomalies and subsequent interpolation by various methods. The problem is illustrated in a heterogeneous study area and contrasting test areas including mountains, low terrains, and a marine area. Provided with realistic error estimates, Least Squares Collocation interpolation of Residual Terrain Model anomalies yields the highest quality gravity grid. In most cases, the Bouguer reduction and other interpolation methods tested are equally viable. However, spline-based interpolation should be avoided in marine areas with trackwise survey data. © 2017 Taylor & Francis Group, LLC

Varbla S.,Tallinn University of Technology | Ellmann A.,Tallinn University of Technology | Mardla S.,Tallinn University of Technology | Gruno A.,Estonian Land Board
Geodesy and Cartography | Year: 2017

Even though the entire Baltic Sea is included in previous geoid modelling projects such as the NKG2015 and EGG07, the accuracy of contemporary geoid models over marine areas remains unknown, presumably being offshore around 15–20 cm. An important part of the international cooperation project FAMOS (Finalising Surveys for the Baltic Motorways of the Sea) efforts is conducting new marine gravity observations for improving gravimetric quasigeoid modelling. New data is essential to the project as the existing gravimetric data over some regions of the Baltic Sea may be inaccurate and insufficiently scarce for the purpose of 5 cm accuracy geoid modelling. Therefore, it is important to evaluate geoid modelling outcome by independent data, for instance by shipborne GNSS measurements. Accordingly, this study presents results of the ship-borne marine gravity and GNSS campaign held on board the Estonian Maritime Administration survey vessel “Jakob Prei” in West-Estonian archipelago in June/July 2016. Emphasis of the study is on principles of using the GNSS profiles for validation of existing geoid models, post-processing of GNSS raw data and low-pass filtering of the GNSS results. Improvements in geoid modelling using new gravimetric data are also discussed. For example, accuracy of geoid models including the new marine gravity data increased 11 mm as assessed from GNSS profiles. It is concluded that the marine GNSS profiles have a potential in providing complementary constraints in problematic geoid modelling areas. © 2017 Vilnius Gediminas Technical University (VGTU) Press.

Gruno A.,Tallinn University of Technology | Liibusk A.,Estonian University of Life Sciences | Ellmann A.,Tallinn University of Technology | Oja T.,Estonian Land Board | And 3 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

Small footprint airborne laser scanning (ALS) is widely used to collect topographic data over large areas. ALS point clouds provide high resolution datasets for variety of scientific and engineering applications, e.g. geomorphology, geodynamics and forestry. ALS can also be used for monitoring coastal processes. For many marine applications, however, the sea surface heights (SSH) are often requested. Satellite altimetry (SA) has been used to monitor SSH globally. But in regional scale, especially in the coastal areas and enclosed water bodies, the usability of SA is limited due to poor accuracy. Alternatively, our experiments have demonstrated that the water surface in the nadir range can be registered using small footprint ALS. Therefore, a special case study was carried out to analyze SSH determination from ALS measurements. Three profile-wise ALS measurements were carried out in the eastern shores of the Baltic Sea. Along flight trajectories 100 m wide corridors of ALS points were formed. Shorter wavelength signals, like sea wave oscillation, were removed by a low-pass averaging filter. The achieved SSH were verified against a high resolution regional geoid model and also with high-frequency tide gauge observations. Comparisons revealed that the ALS-based sea level-corrected SSH agree with the regional geoid model with standard deviation as of ±1-±2 cm. Thus, small footprint ALS measurements could be applied to determine SSH in regions where SA has limited quality, e.g. in coastal areas and enclosed water bodies. © 2013 SPIE.

Mardla S.,Tallinn University of Technology | Oja T.,Estonian Land Board | Ellmann A.,Tallinn University of Technology | Jurgenson H.,Estonian University of Life Sciences
International Association of Geodesy Symposia | Year: 2016

For accurate regional gravity field modelling it is vital to have dense and high quality data coverage. Ice gravimetry is a viable alternative to ship- and airborne gravimetry to help fill gaps over marine areas. A number of factors affect the accuracy of gravimetry on ice, thus special survey and data processing methods are needed. Nevertheless with appropriate methods an accuracy of ±0.16 mGal was achieved on coastal ice. An efficient method for positioning of survey points is RTK GNSS which takes no more than a few minutes on each point and the accuracy achieved is at least ±0.15 cm, while 10min static surveys also yield acceptable results. This study reports ice gravity surveys proceeded on shore-fast ice in the Väinameri Basin, Estonia. Acquired gravity data agree with existing airborne data while covering a larger area. As a result of the survey it was possible to confirm and specify the extents of an area of positive anomalies. An effort to determine the geoid heights over Väinameri Basin directly via using the GNSS data gathered during gravity surveys on ice was made. For now it proved to be less reliable than classical geoid determination from gravity data. © Springer International Publishing Switzerland 2015.

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.

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.

Kall T.,Estonian University of Life Sciences | Oja T.,Estonian Land Board | Tanavsuu K.,Estonian University of Life Sciences
Tectonophysics | Year: 2014

The vertical velocities of the fundamental benchmarks of Estonian 1st order leveling network were estimated, based on the four precise leveling campaigns from 1933 to 2010. The kinematic least squares adjustment of the network was used, where heights and velocities were introduced as unknown parameters. For detection of outliers, Baarda's data snooping method was applied. Estimation of variance components by the Helmert's and the IAUE methods provided realistic weights in the network adjustment and revealed also that the observation errors of the first three levelings are up to 3 times larger than was assumed a priori. To obtain apparent uplift rates and fix velocity in kinematic adjustment, the velocity value +. 2.1. mm/yr of the Ristna tide gauge on island Hiiumaa was transferred to the nearest stable benchmark by using precise levelings from tide gauge to the national height network. Average standard deviation of velocities at benchmarks was estimated to be ± 0.5. mm/yr. Based on apparent vertical velocities of the benchmarks, an interpolated land uplift surface was created using "kriging" and "minimum curvature" gridding methods. Although the two methods gave similar surfaces (RMS of differences was below ± 0.1. mm/yr), the kriging solution was used in comparison with the results of the earlier studies. The uncertainty of new velocity surface was estimated to be ± 0.5 to ± 0.7. mm/yr. The new land uplift model fits well with the Fennoscandian land uplift model NKG2005LU. The RMS of the differences was ± 0.2. mm/yr. Good agreement was also confirmed with the earlier land uplift maps of Estonia (RMS of differences ± 0.6. mm/yr). However, clear disagreement was noticed when tide gauge observations from several studies were used in comparison (RMS of differences up to ± 1.0. mm/yr). Apparently, different velocity solutions of Estonian tide gauges are systematically biased; the reasons for these biases need further investigation. © 2014 Elsevier B.V.

Kollo K.,Estonian Land Board | Kollo K.,Aalto University | Vermeer M.,Estonian Land Board
Geodesy and Cartography | Year: 2011

The article describes a method for deriving the precision of a predicted land uplift value at an arbitrary terrain point which is assumed connected in height to a levelling benchmark using GNSS and a precise geoid model. We derive a statistical model for predicting the uplift rate from the existing point rates along with its empirical signal covariance function. One of our aims is a study on how a land uplift rate model and its empirical covariance function can be determined and then used for calculating changes in height over the time interval between precise levellings or GNSS heightings. © 2011 Vilnius Gediminas Technical University (VGTU) Press Technika.

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.

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