engleski

Geomagnetic field in Croatia-the new results

After more than 50 years the measurements of the geomagnetic field in Croatia have been renewed. During the time interval 2003-2005 a ground survey of total magnetic field intensity in the middle northern part of Croatia has been performed. We analysed in detail these data by carefully undertaken data reduction using the following observatories: AQU, FUR, NCK and THY, which are placed relatively close to the investigated region. The measurements were reduced to the epoch 2004.5 using the one-minute observatories data. We follow an approach of comparison between the two or more observatory time sequences, when one of the observatories is used as a reference one, with known annual mean values of the total field at all observatories. For the secular variation over the investigated area we have used the first order Taylor polynomial over geographic coordinates, and the secular variations at observatories were calculated by using the monthly mean values. The normal geomagnetic field which is the combination of the main field, remanent and induced crustal field has also been estimated by means of first-order Taylor polynomial as function of the geographic coordinates. It filters out the small scale field variations produced by the near-surface magnetic rocks (see [1], [2]). The polynomial coefficients were calculated by regression with three methods of adjustment: simple and weighted least squares fit and adjustment according to the most frequent value. Each adjustment was tested using the Monte Carlo-type stability tests. In order to obtain the distribution of the anomaly field, the core contributions as predicted by the global model were subtracted from the reduced field values.

ground survey; data reduction; normal field; magnetic anomalies

nije evidentirano