Tuesday 23 August 2005
G3
PT0054
Monitoring local crustal movements using high precision GPS network
Ollikainen, Matti1, Ahola, Joel1
1 Finnish Geodetic Institute, Finland
Author email: matti.ollikainen@fgi.fi
The Finnish Geodetic Institute established, in co-operation with the POSIVA Company, three high precision GPS monitoring networks in 1994-95 at the investigation areas, which were selected as candidates for the final disposal of the nuclear waste fuel in Finland. The monitoring networks include one permanent GPS station and 6-9 concrete pillars for episodic GPS observations. Each station has a 2-meter high concrete pillar for the antenna mount. The permanent stations belong the Finnish permanent GPS networkinnRef, which consists of 13 stations. The size of the local GPS networks is approximately 2x2 km. The average distance between two neighbouring stations is about 1 kilometre. The location of the pillars has been observed once or twice per year using 6-7 Ashtech Z-12 GPS-receivers equipped with Dorne Margolin-type antennas. The local GPS networks have now been measured altogether 13-19 times. The rates of the baseline lengths obtained by the least square adjustment are so small that only some of them exceed the accuracy of the determination. The theoretical evaluation of the change rate errors yield the result ±0.1 mm/y, which lead to the conclusion that at two investigation areas there are no baselines with change rates of statistically significant at the confidence level of 95%. At the third investigation area we noticed three baselines with statistically significant change rates. In order to maintain the uniform scale for the GPS measurements made in different years a baseline for electronic distance measurements (EDM) was established at the first investigation area in 2002. The baseline has been measured already six times using precise EDM instruments simultaneously with the GPS observations. The mean difference between GPS and EDM obtained from six simultaneous measurements is (0.7 ± 0.3) mm.
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