Development and field testing of a UHF antenna system for the observation of electrical discharge phenomena in the atmosphere

Abstract

In Japan, the digital terrestrial television broadcasting band (470–710 MHz) is legally protected, resulting in extremely low levels of artificial electromagnetic noise within this frequency range. Therefore, when an antenna is directed toward targets such as cumulus clouds, high-voltage transmission towers, volcanic plumes, or trees, the received signals are highly likely to be ultra high frequency (UHF) event signals—discharge emissions—from those targets. Because discharge phenomena last only tens of nanoseconds, developing instruments capable of directly recording them is technically difficult. Considering Japan’s radio-wave environment and practical hardware constraints, we developed a UHF antenna system with a $0.4\mathrm{ms}$ sampling interval. A dual-integration system was devised and implemented in the backend, enabling continuous recording with no dead time.

Although a $0.4\mathrm{ms}$ interval is long relative to discharge timescales, it becomes a practical method when the objective is not to resolve individual pulses but to detect the collective occurrence of numerous discharge events. The developed system was installed outdoors, and tests confirmed reception of both discharge signals and television broadcasts. Subsequent observations included cumulus clouds, partial discharges from high-voltage transmission towers, small-scale volcanic eruptions, and tree corona discharges. For each target, characteristics consistent with streamers, corona discharges, or partial discharges were obtained. These results suggest that, although improvements are still possible, the compact UHF antenna system developed in this study has the potential to serve as a new observational method for atmospheric discharge phenomena.