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A very particular radio observatory
Rosario Catania 


Author's note: thanks to Renato Romero for his advice, his experience in the field of VLFs and the granting of some parts of text used on this page.


On the slopes of the highest volcano in Europe rises the Etna Radio Observatory (ERO), a project for the reception of radio signals of natural origin at very low frequency, born from the initiative of some independent researchers.
The research team is composed of the radio amateurs Rosario Catania (technician of the microelectronics industry, passionate in volcanology, caving and astrophysics. ), Alessandro Longo (technician of the microelectronics industry, hamateur radio since 1988, electronic hobby) and Renato Romero (started low frequency research at the end of the 1980's, as INSPIRE collaborator) who also covers the role of coordinator, supervised by the volcanologist Salvo Caffo, manager of the Etna Park that houses the station and supported by computer scientists Salvo Spina, also he staff of the Park and Luca Catania (surveyor technician). It all started in 2013 when Rosario decided to use an antenna built by amateur radio Alessandro Longo, already titled of an award for best amateur radio self-construction, to carry out an experiment never tried before, especially in the amateur field, whose main objective was the study of the signals emitted by natural radio sources, but with an "ear" addressed to a potential protagonist, Mount Etna. Opportunity arising from the fact that ERO found hospitality in the vicinity of the volcano, within the headquarters of the Regional Park of Etna. ERO therefore has an ear on the signals coming from space and one that is always alert about the activity of the volcano, which erupts and at the same time explodes (in technical terms, mixed effusive / explosive activity). For this reason ERO represents a unique research opportunity!
By creating a station so close to Etna, the team intends to analyze all the possible radio sources that an active volcano could emit, while remaining in the range of very low frequencies. The observatory therefore carries out an activity on the border between the physical measures of environmental monitoring and radio astronomy, passing through volcanology.


ERO-ETNAPARK Nicolosi site, ex Benedictine monastery (on the right paroxysm of etna)  -  credits:

As mentioned, the main research field of ERO is the very low frequency radio waves (Very Low Frequencies, VLF) which provide information on the physical events that occur on the Earth, in its atmosphere and in the surrounding magnetosphere. That of low frequencies is a theme that has always fascinated researchers, because at low frequencies correspond very long waves, able to penetrate where the normal radio transmissions stop and for the same reason it is a region of frequencies long studied in relation to seismic events. In fact, only a very low frequency signal originating from the rocks of faults under pressure, in the phases that precede a seismic event, would be able to reach the surface crossing kilometers of earth's crust! The signals received at these frequencies are therefore defined as "the voice of the Earth", a sort of window on the planet's global storm activity, on the activity of the magnetosphere that surrounds the Earth, on the effects of solar activity that interacts with the magnetosphere terrestrial, and perhaps also a possible key to understanding some geophysical events such as earthquakes and eruptions. But not just low frequencies!


ERO project today boasts three stations for the detection of natural radio signals and two of these represent an experimental laboratory for the development of new fields of investigation. The three stations are named after the locality in which they operate and are, in order of installation ERO-ETNAPARK, ERO-PENNISI, ERO-SANLEO).

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ERO site stantions -  credits: Google Earth

ERO-ETNAPARK is equipped to receive, analyze and record these radio-natural signals, with a main sensor called technically "SEARC or INDUCTION COIL", translated "Search Coil", flanked by two other devices. The first is a system consisting of two antennas that function as a kind of compass: they are a pair of orthogonal loops, such as those mounted on boats to identify the position of radio beacons and make the ship point, even in the absence of a GPS signal. The second is a vertical geophone, which is nothing more than a floor-standing microphone, but instead of capturing the sounds that travel in the air like a traditional microphone, it captures the sounds and vibrations that propagate in the ground. The vibration is transformed into a weak electrical signal which is then preamplified, analyzed and recorded by the monitoring station.
Working on frequencies of just a few Hz, the geophone is able to "hear" the earthquakes that occur within a radius of over a thousand kilometers, but it is also an ear on the volcano, ready to capture the slightest whisper or tremor unleashed by Etna in the course of eruptions (technically in these cases we speak of paroxysms). From the recorded data of paroxysmal events, it was observed that when the magma begins to rise along the eruptive ducts, even before seeing the surface, it can be detected by the location's geophone, appearing as a rhombus at the frequency of a few Hertz. However, the comparative study of these microphonic signals with electromagnetic fields detected by the SEARCH COIL has not yet detected correlations between volcanic tremors and low-frequency magnetic fields. But the events of a certain seriousness so far monitored have been few and over the years it will be possible to understand if magnetic fields and eruptions are somehow linked and if they can be used as an alert for an imminent eruptive phenomenon. For now ... it would seem not. Networking of signals is currently possible thanks to a PC equipped with a sound card, SpectrumLab acquisition-display software, and a Lan wired connection. (link ERO-ETNAPARK)


Etna summit craters -  credits:

ERO-PENNISI is equipped to receive, analyze and record these radio-natural signals, with a vertical geophone identical to that of ERO-PARK, a camera for monitoring in the volcano optic, and a microwave receiver resulting from a recent collaboration with the company RadioAstroLab srl of Senigallia. The latter, the result of a new idea by Rosario Catania, which has found fertile ground in the whole team, represents a real frontier in the study of volcanic geophysical phenomena, in fact for the first time we face the study of radiation thermal of the volcanic wall, trying to find a correlation with the eruptive episodes. In particular it is interesting to verify if the RAL10TS microwave radiometer produced by RadioAstroLab (operating at 11.2 GHz), connected to the RAL10_LNB outdoor unit positioned on the fire a TV-SAT parabolic antenna, can be used to detect volcanic eruptions. The aim is to measure, with a reasonable degree of reliability and repeatability, the increase in thermal emission due to the hot eruptive spots that occur on the volcanic wall with respect to the "resting" scenario observed by the instrument. The analysis is supported by a simulation that models the measurement system using radiometer response curves measured in the laboratory. It is hoped, despite the inevitable simplifications adopted, to frame the problem by identifying the factors that influence the measure: the results obtained could be a useful starting point for planning experimentation in the field. The remote monitoring system hypothesized for this project is of a passive nature: using a microwave radiometer you receive the natural electromagnetic radiation of the bodies (such as the ground and the atmosphere) emitted due to the temperature and energy interactions between the atoms and the molecules that make them up. The tool observes the scenario, monitoring some significant parameters in order to understand how its state changes over time and according to the environmental conditions. The thermal emission coming from the ground, for example, depends on the product of its physical temperature for the emissivity, a parameter that describes the efficiency of the object to radiate, a function of the chemical-physical characteristics of the material and of the direction of observation. In the microwave band (between millimeter and decimetric wavelengths), contrary to what happens in the infrared, the most significant differences between radiometric measurements are due to changes in the emissivity of the observed region, secondarily to temperature. A very important advantage in the use of microwave radiometer for the study of the environment is that, if well designed and built, it can work automatically for long periods of time, (almost) in all weather conditions and independently of the solar lighting, without request the presence of operators. Networking of the signals is currently possible thanks to a PC equipped with a sound card, the SpectrumLab acquisition-display software, the ARIES acquisition-visualization software and a wired LAN connection. (link ERO-PENNISI)

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Etna lava flow -  credits:

ERO-SANLEO is equipped with modern semiconductor technologies, and uses 3-axis digital accelerometers and microcontroller acquisition systems based on the Arduino and X-Nucleo platform (in collaboration with STMicroelectronics, a leading semiconductor company). Networking of signals is currently possible thanks to a PC, JAMASEIS acquisition-display software and a wi-fi connection. The networking of these data is based on IoT (Internet of Thinghs = Internet of Things). A very special geophone is being developed, a NASA-INSPIRE VLF-3 receiver is being installed, and a microwave receiver for the study of radio-astronomical sources, an SRD receiver for the study of meteorite swarm echoes (for interaction with the French radar signal GRAVES). (link ERO-SANLEO).

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Data collection during an eruption -  credits:

ERO is part of a national network, with other 5 stations, known as VLF OpenLab Observatories, which uses a unified and stable protocol over time, shares data on the network in real time, and has become a reference point also for research important scientific subjects. VLF OpenLab Observatories is the only "unofficial" structure (ie not managed by an institution) that collaborates directly with LIGO (Laser Interferometric Gravitational Observatory) researchers, providing data on the reception of very low frequency during the occurrence of gravitational events . ERO and the other 5 stations, are not able to detect gravitational waves, but are able to receive the magnetic field at the same frequency, which represents one of the boundary conditions of the entire theory on gravitational waves, and for this reason, after each gravitational event so far detected, LIGO requested the data of ERO and of the other 5 stations, to be integrated in the context of the study.


Receiver construction and setup operations -  credits:

Throughout the year 2015, ERO and the other stations on the network were involved in a research project called Opera 2015 (Permanent Observatory on Radiosism Emissions), a unique campaign of measures that saw the use of the sensor structure of the entire network in search of seismic radio precursors. In other words, there was a search for very low frequency radio tracks, concomitant or even earlier than earthquakes, based on the over 15,000 events detected by INGV during the year. The study allowed the elaboration of a calculation tool called Radiosismic Index (RI), which practically defines the possibility or not to detect radio signals before an earthquake based on two parameters: the distance from the event and the intensity of the earthquake. The results of the campaign were in line with those of most studies carried out to date: the confirmation of a very restricted area around the epicenter, in which it is possible (with great difficulty) to detect associated magnetic anomalies. This also explains why today, although many efforts have been made in this direction, an earthquake forecasting method based on very low frequency radio emissions is unfortunately far from being developed.


Radio-seismic Emission Permanent Observatory (OPERA)-  credits:

The future of ERO involves maintaining the structure, with the systematic collection of data on low-frequency electromagnetic activity 24 hours a day, of microwaves and sharing them with other researchers.
Today the ERO project boasts collaboration with professional researchers such as Alessandro Bonforte (Volcanologist and Geophysicist Researcher at National Institute of Geophysics and Volcanology - Etnean Observatory), Roberto Maugerie (MD in Geological Sciences Technologist at National Institute of Geophysics and Volcanology - Etnean Observatory), and professional technicians such as Flavio Falcinelli (Electronic, passionate about science and always an experimenter) and Federico Scremin (Aircraft avionics engineer, expert in telecommunication).


Electromagnetic wave dedicated to James Clerk Maxwell-  credits: ploufandsplash  (common wikipedia)

Some links to learn more

The ERO Team:
The ERO project:
ERO online data:
The VLF Openlab portal:
ERO's participation in the OPERA2015 project:
The OPERA2015 project
The SpectrumLab signal processing software:
The ARIES signal processing software:

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