Secular variation on the territory of the Czech Republic and reduction of the magnetic survey to the epoch 2008.5

Paper type: 
Oral presentation

Secular variation on the territory of the Czech Republic and reduction of the magnetic survey to the epoch 2008.5

 

Pavel Hejda, Josef Horacek and Tomas Bayer

 

Instituteof Geophysics of the ASCR, Prague, Czech Republic

 

A recent stage of the magnetic surveying activities in the Czech Republic was started in the fifties by setting up a fundamental network of the first order. It consists of 199 points, which have been stabilized by means of granite boundary stones.

Measurements of the vertical and horizontal components were carried out in 1957-58 and supplemented by reduced values of declination obtained at a former campaign. The network was re-occupied in 1976-1978 when three components D (by Matting & Wiesenberg theodolite), H (QHM) and Z (BMZ) were completed by the measurements of the total field F (by PPM). The latter enabled to correct random errors. The last magnetic survey in 1994-96 was carried out by a fluxgate theodolite and a proton precession magnetometer. All values were reduced to the epoch 1995.5

Since 1970 six selected point have been reoccupied approximately every 2 years. Five of them are situated close to the Czech boundaries, the last one in Eastern Bohemia. The repeat station network was completed by station Myto (Western Bohemia) in 2003. Eight series of measurements are carried out at every station. All measurements are reduced to annual means centered to the middle of the year in which the station was measured using data from geomagnetic observatory Budkov. No on-site variometer is used. The measurements were usually carried out in odd years (1999, 2001, 2003). According to the recommendation of the first Workshop on European Repeat Station Measurements held in Niemegk in 2003, the term was changed to even years, starting from 2004.

The repeat station measurements, together with the data from neighboring observatories, were now used to reduce the data from the last magnetic survey to the epoch 2008.5 and new magnetic charts were drawn.

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