Wpływ miast i terenów zurbanizowanych na jakość pomiarów naturalnych pól magnetycznych
The impact of cities and urban areas on the quality of natural magnetic field measurements

Summary/Abstract: An increase in electromagnetic radiation, across all frequency bands, has been one of multiple effectsof recent developments in the power supply to rapidly growing urban areas in Poland. This hasimpacted measurements in a range of scientific disciplines, such as astronomy, geophysics, physics ofthe atmosphere and meteorology, which use electromagnetic observations as research tools.The paper introduces a methodology used by the Krakow-based ELF group since 1992 to measurethe magnetic component of the ELF (below 3000 Hz) (http://www.oa.uj.edu.pl/elf/ index.html). Theefforts began with expedition measurements that have identified the best location for a fixed measurement station. It was established in 2005, near Zatwarnica in the Bieszczady Mountains, and named afterits location in the Hylaty stream valley. The methodology of analysis is also discussed with the signalspectrum being the main tool used to determine data quality and thus providing a quantitative way of assessing the contribution of human-originated electromagnetic contamination in the ELF band, namelylarge urban areas, power grids and electric railway lines. The paper analyses the quality of the data collected using the results of measurements taken at Hylatyin 2004–2015. Examples of dynamic spectra are also shown featuring signatures from phenomenaand processes in the atmosphere, ionosphere and magnetosphere. Atmospheric discharges, which occurat a rate of 44 per second on a global scale, are the dominant natural source of electromagnetic waves inthe atmosphere. This activity induces the spherical Earth-ionosphere resonator and, as a result, the EM wave spectrum reveals characteristic peaks known as the Schumann resonance (with the first peak of~8.0 Hz). Another highly characteristic, but rarely observed signature is provided by peaks from theinduction of the Ionospheric Alven Resonator (IAR) cavity. These peaks have a frequency between 1 and5 Hz. The resonator consists of two layers of the ionosphere with a high electron density gradient. TheIAR can only be observed in the evening and at night and only during certain phases of solar activity.The magnetosphere contributes ELF signals from so-called magnetic storms. They are triggered bychanges in the solar wind, which cause distortions in the Earth’s magnetic fields resulting in a broadbandincrease in the registered signal across the 1–3 Hz frequency.The study concludes that contamination from cities and other urban areas makes their spatial locationkey in the search for electromagnetically pure areas. The authors identified such potential areas to belocated in the central sections of the Pomeranian and Masurian lake districts and along sections of theeastern Polish border.

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