Abstract
In this paper, the amplitude probability density (APD) of the wideband extremely low frequency (ELF) and very low frequency (VLF) atmospheric noise is studied. The electromagnetic signals from the atmosphere, referred to herein as atmospheric noise, was recorded by a mobile low-temperature superconducting quantum interference device (SQUID) receiver under magnetically unshielded conditions. In order to eliminate the adverse effect brought by the geomagnetic activities and powerline, the measured field data was preprocessed to suppress the baseline wandering and harmonics by symmetric wavelet transform and least square methods firstly. Then statistical analysis was performed for the atmospheric noise on different time and frequency scales. Finally, the wideband ELF/VLF atmospheric noise was analyzed and modeled separately. Experimental results show that, Gaussian model is appropriate to depict preprocessed ELF atmospheric noise by a hole puncher operator. While for VLF atmospheric noise, symmetric α-stable (SαS) distribution is more accurate to fit the heavy-tail of the envelope probability density function (pdf).
Highlights
Low frequency (ELF, defined here as 300–3000 Hz) and very low frequency (VLF, defined here as 3–30 kHz) radio waves have efficient long-range propagation in the so-called earth-ionosphere waveguide [1] and comparatively deep penetration into conducting medium such asEarth and seawater
Statistical and fitting experiments are performed for the processed data to investigate the wideband model of the extremely low frequency (ELF)/VLF noise and initial results are derived in this paper
It can be seen that the low frequency components caused by baseline wandering are suppressed efficiently by wavelet denoising and the harmonics are further suppressed after least square (LS) estimation, which validates the effectiveness of the proposed method
Summary
Low frequency (ELF, defined here as 300–3000 Hz) and very low frequency (VLF, defined here as 3–30 kHz) radio waves have efficient long-range propagation (attenuation rates typically a few dB/Mm at VLF and much smaller, of the order of a few tenths dB/Mm at ELF) in the so-called earth-ionosphere waveguide [1] and comparatively deep penetration into conducting medium such as. Traditional analysis and modeling for ELF/VLF noise are concentrated on narrow-band characteristics (typical bandwidth is 5% of the center frequency). Magnetic field sensors are preferred for receiver instead of electric field sensors because they can provide superior noise response at the low end of the frequency range [8]. The noise floor of the receiver with the same bandwidth over the ELF/VLF range of interest (1.5∼4.5 kHz) will increase significantly. The SQUID based optimal receiver cannot be derived for the wideband communication using ionosphere heating. We adopted a low-temperature SQUID receiver to observe ELF/VLF atmospheric noise during seven days. Statistical and fitting experiments are performed for the processed data to investigate the wideband model of the ELF/VLF noise and initial results are derived in this paper
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