Anomalous Long-range Propagation of VHF NAV signals by the sporadic E

Abstract

The sporadic E (Es) layer is a layer in the ionospheric E region with a dense electron density and thin altitudinal thickness at altitudes around 100 km. It has been pointed out by International Civil Aviation Organization (ICAO) that the Es layer has a potential to introduce anomalous long-range propagation in the frequency band of aeronautical navigation and communication (EsAP: Es Anomalous Propagation). In order to reveal the detailed characteristics of EsAP, we have constructed a network of instruments for continuously monitoring the intensities of radio waves of various VOR and ILS LOC stations in Japan. In this paper, we introduce the following latest results obtained using data from this monitoring observation: 1) derivation of statistical characteristics (seasonal/local time dependence) of EsAP occurrence probability, 2) mapping of the spatial structure of Es in 2D by combining EsAP observations with GPS-TEC ROTI data, and 3) detailed investigation of the long-range propagation of ILS-LOC signal from Taiwan. We also discuss the possibility for using the anomalous propagation of VHF NAV signal for studies of equatorial plasma bubbles, a different phenomenon in the ionospheric F region.