Tallinn, Estonia
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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.

Oja T.,Estonian Land Board | Turk K.,Estonian University of Life Sciences | Ellmann A.,Tallinn University of Technology | Gruno A.,Estonian Land Board | And 2 more authors.
8th International Conference on Environmental Engineering, ICEE 2011 | Year: 2011

Recently the Estonian gravity datasets have been thoroughly revised by the joint research group. The purpose of this study was on assessing the quality of historic gravity data observed on the bottom of the Gulf of Riga from 1966 to 1967 and on the frozen Lakes Võrtsjärv and Peipsi from 1986 to 1987. For the evaluation of historic gravity datasets, new gravity campaigns were carried out on large ice-covered Lakes Peipsi and Võrtsjärv in winter 2009 and on the ice of sea along the Gulf of Riga coast in winter 2010. Scintrex CG5 and LaCoste&Romberg (LCR) G relative gravimeters in combination with GPS RTK positioning were used for determining gravity values and position of the survey sites. The measuring conditions in an open ice field are generally unfavorable for precise gravity surveys, since the determination of the mass sensor position of relative gravimeter is a challenge on top of the oscillating surface of ice sheet. Therefore special equipment and methodology need to be chosen to assure correctness of measurements and data processing. Gravimeters LCR G191 with variable-damping screw at the bottom and Scintrex CG5 (No 36 or 10092) with 6 Hz digital data recording system were used during these ice field campaigns. The recorded 6 Hz "raw" readings of CG5 proved to be particularly helpful for studying the effect of oscillating elastic ice sheet. The plot of these readings showed peak-to-peak amplitudes up to 160 mGal and the spectrum of the same data revealed that oscillations occurred mainly at frequencies from 0.05 to 0.35 Hz. Despite harsh environment, the uncertainty of gravity values about ±0.15 mGal (1.5·10-6 m/s2) was achieved from the least squares adjustment of observation data. The evaluation of historic data on the basis of accurate control points from the new surveys revealed some larger discrepancies in the Gulf of Riga. However, no systematic biases were found in the study areas. © Vilnius Gediminas Technical University, 2011.

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.

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.

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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