Modeling of Doppler‐shifted terrestrial VLF transmitter signals observed by DEMETER

Abstract

Observations of signals from a terrestrial very low frequency (VLF) transmitter made by the DEMETER spacecraft inside the plasmasphere are modeled using a three‐dimensional wave propagation code. The simulation results agree well with the satellite measurements, predicting both the incidence and frequency offset of Doppler‐shifted signals resulting from non‐ducted interhemispheric propagation paths through the plasmasphere. The observed Doppler shifts are similar to those which can result from linear mode coupling as VLF transmitter signals scatter from small‐scale plasma density irregularities. Thus care must be taken to differentiate the two effects when studying the power loss of VLF waves through the ionosphere. The agreement shown between predictions and observation demonstrates the utility of the models used for understanding the wave energy distribution in the plasmasphere from terrestrial transmitters.