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Current practice of the Hungarian Repeat station surveys: measurement, data processing, interpretation |
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Kovács, P. (1), Csontos, A. (1), Vadasz, G. (2), Heilig, B. (1) |
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(1) Mining and Geological Survey of Hungary, Budapest, Hungary, (2) Statistical and Biological Physics Research Group of Eotvos Lorand University, Budapest, Hungary |
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In Hungary, the geomagnetic survey campaigns possess a long tradition, dating back to the middle of the nineteenth century. Since 1950 onwards, until 1995, Hungary’s vector magnetic components have been surveyed periodically, every 15 years, on the so-called country survey (CS) network comprising 300 stations. In 1965, a repeat-station (RS) network comprising 15 non-anomalous stations was also installed in order to monitor the spatial distribution of the secular change of the magnetic field and to regularly update the field measured in the dense country network. The RS network stations are occupied in 2-3 years of periodicity. In the paper, we present the RS network of Hungary, the procedure of the temporal reduction of the RS vector observations, as well as the spatial adjustment of the reduced RS data. Traditionally, the normal field models of Hungary are constructed by the first- or second-order polynomial of the geographic coordinates. The polynomial fitting (PF) is carried out separately for each of the vector component, thus this solution ignores the Laplace’s condition that should be valid for the internal geomagnetic field. Moreover, PF doesn’t take in account the radial change of the field, and disregard the curvature of the modelled area. To avoid these shortcomings, recently, we have developed a Matlab code for the application of the adjusted spherical harmonic analysis (ASHA), introduced by De Santis (1992) for the modelling of the geomagnetic field for a domain extending to a spherical cap. We also apply the revised spherical harmonic analysis (R-SCHA) pioneered by Thebault et al. (2006) that is able to exemplify the geomagnetic field model in a conical domain by involving geomagnetic observations from different altitudes (ground, airborne, spacecraft). In the paper we compare the geomagnetic models obtained by the different methods on the basis of their accuracies and physical relevancies. The temporal reduction of the Hungarian RS data is carried out by the use of the variometer records of the Tihany observatory. However, it is also considered that in stations located far from our reference observatory, the accuracy of the reduction can be eventually increased by the installation of an on-site variometer. The site of the variometer station must be carefully selected in order to ensure low level of magnetic and mechanical noise, as well as temperature stability. During the last three repeat-station campaigns of Hungary carried out in 2012, 2014 and 2016, a three-component DIDD magnetometer was installed in the Baradla cave, near to our Aggtelek repeat station. The paper presents the variometer site, the installation of the DIDD variometer and the results of the recordings. The improvement of the reduction accuracy is also shown by comparing the reduced RS magnetic components obtained with and without the use of the DIDD variometer records. |
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Measurements |
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no preference |
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