Determining the Amplitude Transfer Function of the Permanent Magnetic ELF Measurements of the Széchenyi István Geophysical Observatory

In July 2020, a detailed ELF/VLF noise test was carried out in the Széchenyi István Geophysical Observatory. This test included the temporary installation of a pair of LEMI-type induction coil magnetometers that run from a battery during the test period (9 July 2020) when the power supply of the observatory was gradually shut down. As the temporary coils were installed two days before the test day (7 July) and continued to operate until the 13rd of July, there were several days when both the permanent and temporary systems were in operation. In this study, we use this overlapping period to further investigate electromagnetic noises present in the observatory and to determine the amplitude transfer function of the permanent ELF-band recording system based on the calibrated temporary measurements.