ERO change in the level of electromagnetic environmental noise following the #COVID-19 lockdown

ero analisi rumoreantropico coronavirus coil ridINGV and ERO (Etna Radio Observatory) are cooperating for observing and studying the Electromagnetic signals. They are mainly related to the solar-ionosphere interaction and we continuously check for a possible relation with seismic and volcanic activity. ERO is equipped with different antennas, sensitive to the VLF, ULF and ELF spectrum and performs a continuous recording.
We are pleased to share with you a short analysis of our Nicolosi station, in particular the signals received by the induction COIL antenna, which is an antenna sensitive to very low frequencies, close to the Hertz!
We have been inspired by an article, published on the INGVterremoti Blog, analyzing the variation of environmental seismic noise, following the lockdown due to the COVID-19 emergency.
We produced the spectrograms from February 22 to March 31 by using the Spectrum Lab free software, to analyze the data from 08- to 10 (UTC), considering that these are usually the hours showing the highest level of anthropogenic noise.
A spectrogram is a simple and useful graphic representation of the frequency content of a signal as a function of time. A spectrogram is plotted putting the time on the X-axis, so it can be read normally, scrolling it from left to right. Frequencies are plotted vertically versus the Y-axis, from lower to higher. The frequency content and distribution is instead represented by the color code, lighting more the more abundant frequencies.
The idea of understanding how the noise generated by human activities of human activities affect the quality of the electromagnetic (EM) signal received by the antenna, has aroused us a lot, so we have analyzed the data of our archives .
OBJECTIVE: to understand if the forced decrease in human activities due to the lockdown for COVID-19, has in any way influenced the quality of the EM signal received by the station and how.
ANALYSIS: we show here the spectrograms of the data recorded by the induction COIL antenna in a vertical sequence from February 22 to March 31 (from top to bottom), in the hours between 08-10 am, considering that this daily time window is generally the one with the highest level of anthropic noise.
RESULTS: There is a certain correlation, evident from Saturday 21 March. In the previous days, we can see such a noise reduction only on Saturday and Sunday days. The strong disturbance recorded on March 25th is due to heavy rain and very bad weather. In the lower plots, we can clearly see the noise disappearing with the stop to the activities.

ERO Fig1

Fig. 1 - Spectrogram relevant to March 3, 2020 (UTC Time)

ERO Fig2

Fig. 2 - Spectrogram, relevant to March 30, 2020 (UTC Time)

CONCLUSIONS: Anthropogenic noise is part of those "boundary conditions" which define a large part of the quality of the signals we receive daily. This noise cannot be neglected or eliminated, but now, at least, we can discriminate it from the rest and try to better understand its characteristics. In the near future, we will surely take this occasion to perform a deeper analysis of the anthropic noise in order to understand more precisely how it affects our recordings and if and how it can be, at least, filtered in the future.

ERO Fig3

Fig. 3 - In this figure, we evidenced with the boxes the noise related to human activities on March 03 (UTC Time).

ERO website link: http://www.etna-ero.it
Link to seismic noise article: https://ingvterremoti.com/2020/04/01/variazione-del-le-le-diore-ambientale-in-seguito-ai-decreti-per-lemergenza-covid-19/