Measurements of Nighttime Ionospheric E and F Layers Using AM Radio Signals

Commercial AM radio transmissions (0.54–1.7 MHz) in the medium-frequency (MF, 0.3–3 MHz) band provide a promising yet underexplored resource for ionospheric remote sensing. Building on previous work, this study aims to distinguish different variabilities in E and F layers of the nighttime ionosphere using AM radio signals. Distinct nighttime ionospheric dynamics at E- and F-layer altitudes are revealed during a September 2024 field campaign over the southeastern United States, with the dominant layer shifting over the course of a night. Doppler measurements of MF skywaves show that E-layer reflections exhibit smaller and faster variations (typically <0.05 Hz amplitude, periods <10 min), corresponding to inferred vertical velocities below 9 m/s, while F-layer reflections show larger and slower variations (typically >0.1 Hz amplitude, periods >10 min), corresponding to vertical velocities up to 40 m/s. This contrast is consistent with altitude-dependent gravity-wave activity. These layer-specific observations are enabled by a passive workflow combining spectrogram-based Doppler measurements, virtual heights retrieved from the audio delay between groundwave and skywave at time-synchronized close and remote receivers, and carrier phase tracking that provides enhanced sensitivity to small E-layer Doppler shifts (<0.01 Hz).

Duke Scholars

Author Yunjiao Pu  

Author Steven A. Cummer Pierre R. Lamond Department of Electrical and Computer Engin ...