Low-frequency Atmospheric Noise Research Articles

Statistical Analysis of Very Low Frequency Atmospheric Noise Caused by the Global Lightning Using Ground‐Based Observations in China

AbstractBased on the very low frequency (VLF) signals observed on the ground in mid‐latitude areas of China from February 2016 to February 2019, atmospheric noise in the 3–30 kHz band is investigated in detail. The statistical analysis indicates that the seasonal variations of the atmospheric noise of different bands are similar in the general trend but different in magnitude, the largest of which can reach 10 dB. According to the accuracy analysis of the atmospheric noise model by the Consultative Committee of International Radio (CCIR), despite the valid long‐term variation of the atmospheric noise provided by the CCIR at the observation station, it overestimates the atmospheric noise level and thus, is unable to show the detailed characteristics of the short‐term variation of the atmospheric noise. Combined with the global lightning observation, the correlation between atmospheric noise and global lightning activities is analyzed to find that the lightning within a range of 3,500 km can dominate the atmospheric noise at the observation site, along with distant lightning playing a minor role. Not only do the results deepen our understanding of the distribution of atmospheric noise in mid‐latitudes in China, but they also reveal the correlation between atmospheric noise and global lightning, thereby benefiting the study of VLF signal propagation and its communication application.

FPGA implementation of hardware efficient adaptive filter robust to impulsive noise

Adaptive filters are prevalent in many real-time signal processing applications. Many adaptive algorithms already exist, but most of them assume white Gaussian noise as disturbance. However, for many applications such as electrocardiogram, foetus heart rate measurement, low frequency atmospheric noise, underwater acoustic noise and signal measurement in instrumentation, the impulsive noise is more common. This study presents a modified robust mixed norm (MRMN) adaptive filter algorithm robust to impulsive noise with higher convergence rate and lower steady state error (SSE). MRMN adaptive filter algorithm has been simulated using Matlab and Xilinx system generator high level synthesis tool and a significant improvement in SSE and convergence speed is obtained compared with the existing adaptive filter algorithms for similar specifications. The proposed algorithm is also described using VHDL and synthesised using Xilinx synthesiser tool in order to implement on field-programmable gate array (FPGA). The FPGA post route and place implementation results show nearly 90% reduction in resource utilisation and nearly 2.6 times improvement in clock frequency as compared with the existing FPGA based implementation for similar specifications.

Statistical Characters Analysis of LF Atmospheric Noise

In low frequency (LF) communication, the main factor of affecting property of LF communication system is the atmospheric noise caused by lightning phenomenon. Amplitude probability distribution of this atmospheric noise is with non-Gaussian characters seriously. Due to influence of various factors, such as occurrence time, physical location and seasons, making analysis of LF atmospheric noise on the receiver communication performance becomes more complex. Therefore, the study of characteristics of atmospheric noise amplitude probability distribution is necessary. In this paper, Firstly, we are on the assumption that the amplitude probability distribution characteristics of atmospheric noise obey Alpha stable distribution; then introduce the Alpha stable distribution model; Finally, we use probability distribution function (pdf) and Quantile-Quantile (Q-Q) plot fitting for Alpha stable distribution according to real LF channel noise data acquired by a high sensitive superconducting quantum interference device (SQUID). Simulation results show the assumption is correct.

The effective antenna noise figure Fa for a vertical loop antenna and its application to extremely low frequency/very low frequency atmospheric noise

Expressions tabulated for the effective antenna noise figure Fa usually assume an electric field antenna, since most measurements of radio noise are made on the electric field of the noise. Furthermore, the International Radio Consultative Committee (CCIR) noise model predictions for Fa are made only for electrically short grounded vertical monopoles over a perfect ground. However, at frequencies lower than those traditionally used for communications, i.e., at extremely low frequencies (ELF; frequencies in the range 3 Hz to 3 kHz) and very low frequencies (VLF; frequencies in the range 3–30 kHz), it is common for magnetic field loop antennas to be used, and the tabulated expressions for Fa do not apply. This communication reports the derivation of an expression for Fa as measured by a small vertical magnetic loop antenna and its subsequent application to ELF/VLF radio noise measurements made at a variety of locations around the world. There is good agreement between the measured Fa values and estimates of maximum and minimum Fa values for the ELF/VLF range published by Spaulding and Hagn in 1978, but an improved fit to the measurements can be obtained by making moderate adjustments to the maximum and minimum values at both the low (10–100 Hz) and high (8–32 kHz) frequency limits.

Search for Primordial Perturbations of the Universe: Observations with Ratan-600 Radio Telescope

All kinds of primeval perturbations of the Universe should result in fluctuations of the microwave background radio emission. Here we report our latest upper limits to these fluctuations on scales 5′ to 3°. Using the new 600-m Soviet Radio Telescope we obtained a mean temperature profile of the region from 08h to 15h in R.A., centred at the declination of the Coma Cluster. 20 good records of this region were used in the final reduction of the data. After “normalization” of these data by filtering out low-frequency atmospheric noise and “bursts” which exceed the 4σ level we calculated an upper limit to the fluctuations of the microwave background radiation.

Solar flares and atmospheric noise

In this paper, the effects of solar flares on low-frequency atmospheric noise are examined. Relations between the rise of noise, and the area of the flares its intensity, location on the sun, and time of day are studied. Noise levels preceding flares are also examined to determine whether there are any phenomena which may be used for the prediction of high-frequency fade-outs.

Sudden Decrease in Low-frequency Atmospheric Noise during the Cosmic-Radiation Storm of February 23

AT Churchill, Manitoba (lat. 58.8° N., long. 94.2° W.), an unusual event occurred on the 100-kc./s. atmospheric noise recordings on the morning of February 23. Churchill is situated near the region of maximum intensity of the auroral zone.