Current practice

of the Hungarian Repeat station surveys: measurement, data processing,


Kovács, P. (1),

Csontos, A. (1), Vadasz, G. (2), Heilig, B. (1)

(1) Mining and Geological Survey of Hungary,

Budapest, Hungary, (2) Statistical and Biological Physics Research

Group of Eotvos Lorand University, Budapest,



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.