ELF receiver for EM waves beyond 46 Hz |
Čop, R. |
Institute Sv. Peter, Sv. Peter 115, 6320 Sečovlje, Slovenia |
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The preliminary measurements on the territory of Slovenia showed that, on this part of Europe, the great value of noise is presented in the geomagnetic field. In order to meet international recommendations we chose only the magnetometers for one-second results of measurements for our geomagnetic observatory PIA (Piran, Slovenia).
For better registration of geomagnetic pulsations, natural resonant frequencies of the Earth and conditions in ionosphere we constructed a broadband ULF/ELF (Ultra Low Frequency / Extremely Low Frequency) receiver (Earth Receiver). It receives the frequency range from 1 mHz to 46 Hz. The frequency range of measurements is in the transition from the Earth’s magnetic field, which arises within the interior of our planet, into the measurement of the electric field, which arises primarily in the Earth’s atmosphere. It covers the wavelength Gm (length ~ 109 m), which are waves of magnetic pulsations, and the wavelength of Mm (lenght ~ 109 m), which are the waves of natural resonance of the Earth. The natural resonant frequencies originating from electric resonators of the Earth have been explored since the middle of the past century and are relatively poorly known. Geomagnetic pulsations, which originated from space and magnetosphere, have been studied more than two hundred years. The frequencies of geomagnetic pulsation are mainly influenced by changes in the orientation of the interplanetary magnetic field and change in the speed of solar wind. Due to interference, these waves appear on the Earth’s surface as sudden changes in the magnetic field of different frequencies, amplitudes, phases and polarizations. Because they do not depend only from solar wind but also from geological conditions at the site of measurement, they are also good detector of internal structure of lithosphere of the Earth and hydrological researches.
We adopted the construction of our Earth Receiver to the specific conditions of our territory. There is the highest density of electric discharges in atmosphere in Europe and also seismic active area. For the same reason we adopted also its installation on our observatory. Measurements from Earth Receiver at the observatory beyond the frequency of 1 Hz are parallel measurements of magnetometers. We initially studied the conditions with antenna of receiver orientated vertically. The frequency range from 5 Hz to 50 Hz has great content of electromagnetic noise of artificial source. Except for controlling the EM pollution of our environment, ULF/ELF receiver is also suitable for: a) monitoring of atmospheric discharges and cores of storms; b) electric discharges into the ionosphere; c) earthquake monitoring; d) determination of the influence of magnetic pulsation on biosphere and; e) monitoring of climate changes. The Earth Receiver is the only measuring instrument for monitoring seismic events, which is placed directly in the origin of earthquake disorders.
The global ULF wave power index is calculated from the measurement data of magnetometers on the Earth's surface and on geostationary and interplanetary satellites. It is in direct correlation with the speed of the solar wind and therefore is very suitable for the presentation of the situation in the space in vicinity of the Earth (Space Weather). But it is in very poor correlation with geomagnetic indices and should therefore be appropriately adapted to monitor the phenomena in the Earth's surface and lithosphere. |
Measurements |
oral |
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