VHF Interferometry System for Detecting Anomalous Propagation of FM Radio Broadcasting Wave Related to Earthquake and its Preliminary Result

Earthquake-related anomalous electromagnetic phenomena have been reported in various frequency ranges in a few decades. Investigation on the anomalous propagation of VHF transmitter waves is one of promising approaches on the short-term prediction and crustal activity monitoring. The anomalous propagation is considered to be generated by disturbances of the atmosphere above the epicenter or along the propagation path prior to large earthquakes. Consequently, over-horizontal propagation has been received. A recent study shows that the appearance of anomalies was significantly enhanced within 5 days before earthquakes with M ≥ 4.8. However, there is no information on the scattered place, that is, the direction of wave arrival. Therefore, a simple interferometer system for VHF radio wave to identify the position between space-time of earthquake-related atmospheric disturbances has been developed and installed at Chiba University. In this paper, we will show you the developed interferometer system and results of fundamental tests to evaluate the performance of developed and installed interferometer at Chiba. In addition, facts on invisible propagation of VHF radio wave obtained from 1-year continuous measurement at Chiba are described in this paper. Those are possible radio duct propagations and possible earthquake-related anomalous propagations.