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| Titel |
Improving the terrestial gravity dataset in South-Estonia |
| VerfasserIn |
T. Oja, A. Gruno, A. Bloom, E. Mäekivi, A. Ellmann, T. All, H. Jürgenson, M. Michelson |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028936
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| Zusammenfassung |
| The only available gravity dataset covering the whole of Estonia has been observed
from 1949 to 1958. This historic dataset has been used as a main input source for
many applications including the geoid determination, the realization of the height
system, the geological mapping. However, some recent studies have been indicated
remarkable systematic biases in the dataset. For instance, a comparison of modern
gravity control points with the historic data revealed unreasonable discrepancies in a
large region in South-Estonia. However, the distribution of the gravity control was
scarce, which did not allow to fully assess the quality of the historic data in the study
area.
In 2008 a pilot project was called out as a cooperation between Estonian Land
Board, Geological Survey of Estonia, Tallinn University of Technology and Estonian
University of Life Sciences to densify the detected problematic area (about 2000
km2) with new and reliable gravity data. Field work was carried out in October and
November 2008, whereas GPS RTK and relative Scintrex gravimeter CG5 were used for
precise positioning and gravity determinations, respectively. Altogether more than
140 new points were determined along the roads. Despite bad weather conditions
and unstable observation base of the gravimeter (mostly on the bank of the road),
uncertainty better than ±0.1 mGal (1 mGal = 10-5 m/s2) was estimated from the
adjustment of gravimeter’s readings. The separate gravity dataset of the Estonian
Geological Survey were also incorporated into the gravity database of the project
for further analysis. Those data were collected within several geological mapping
projects in 1981–2007 and contain the data with uncertainty better than ±0.25
mGal.
After the collection of new gravity data, a Kriging with proper variogram modeling was
applied to form the Bouguer anomaly grids of the historic and the new datasets. The
comparison of the resulting grids revealed biases up to -4 mGal at certain regions. Therefore
it is strongly recommended to replace the historic gravity dataset with new one for
forthcoming gravity field and geoid modelling works. |
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