GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.1 - POSTER GNGTS 2023 A month of VLF detection at Mefite, Valle D’Ansanto, Italy G. Cianchini 1 , C. Fidani 1,2 , A. De Santis 1 , L. Perrone 1 , A. Piscini 1 , M. Soldani 1 , S. D’Arcangelo 3 , A. Nardi 1 , M. Orlando 1 , D. Sabbagh 1 1 Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy 2 Central Italy Electromagnetic Network, Fermo, Italy 3 Dept. of Physics of the Earth and Astrophysics, Faculty of Physics, UCM, Madrid, Spain The Central Italy Electromagnetic Network (CIEN), starting in 2006, implemented instruments to monitor electric fields in the atmosphere (Fidani, 2009, 2010). The simple detector was constituted by outdoor sensors and an indoor recording system. Sensors were composed of horizontally suspended electrode wires connected to wide-band amplifiers (Fidani, 2021). The recording system consisted of a standard PC audio card and the software suitable to both carry out a real-time analysis and store data. Wide-band amplifiers operated in the ELF (3-300 Hz), VLF (0.3-30 kHz), and LF (30-300 kHz) bands. Specifically, the detector demonstrated its capability to monitor many sub-ionospheric signals from different VLF and LF transmitters simultaneously and with only one device (Fidani, 2011; Siciliani et al., 2013). This was possible thanks to an amplifier working far from the resonance condition, and thanks to the Fourier manipulation by Spectrum Lab software (DL4YHF, http://www.qsl.net/dl4yhf/spectra1.html ). VLF and LF radio transmitters in the range of 10-100 kHz are typically reflected from the lowest ionospheric layer. They are useful for communication and navigation (the VLF band, Casselman et al., 1959), and time comparison purposes (the LF band, Blair et al., 1967). The lines between the transmitters and the receiver were considered electromagnetic propagation paths. It was demonstrated that when one end (or both ends) of a propagation path are at an elevated position, the uses of transmitting and receiving antenna orientations other than vertical (Pappert and Bickel, 1970) allow obtaining a high gain of the detected signal. This property was of particular importance for wave monitoring by horizontal electrodes, such as those utilized by the CIEN to detect many far transmitters. Moreover, the capability of Spectrum Lab to operate spectrum selections by simple command lines, permitted to save power amplitudes of every wave interval and at every time to text files. In May 2022, at the lake “Mefite” geosite, INGV Team installed a stand-alone multi-parameter infrastructure (named “Mefite station”) equipped with different instruments to detect underground fluid motion. This is the result of the synergy between two INGV Projects - FURTHER and CHOPIN - to monitor crustal fluid migrations associated with tectonic activity. The equipment consists (among others) of a fluxgate three-component magnetometer (LEMI 18), a vertical