First Results from VIPER The VLF Trans-Ionospheric Propagation Experiment Rocket Campaign

The transmission of terrestrial VLF emissions through the ionosphere has a measurable and often significant effect upon both energetic and relativistic electron populations in the magnetosphere. Both natural (e.g. lightning transients) and artificial (e.g. ground VLF transmitter radiation) sources contribute significantly to these VLF emissions. Models exist of this VLF penetration process, and satellite measurements show the spatial and diurnal variations in wave amplitudes at the upper bounds of the ionosphere (600-800 km altitude). However, no measurements of the actual electrodynamics of the attenuation and propagation process from the interior of the Earth-Ionospheric waveguide, through its boundary in the D and E region of the ionosphere, and into the ionosphere and magnetosphere above currently exist. With this deficit in the observational database in mind, on 26 May 2021, we flew the VIPER sounding rocket out of the NASA Wallops Flight Facility through the nighttime D and E region, up to an altitude of 160 km. The VIPER payload carried a fully 3D EM field measurement and relevant plasma, and neutral particle measurements through the radiation fields of an existing VLF transmitter (USN call sign NAA; 24.0 kHz; Cutler, Maine) in order to explore the electrodynamics of the VLF absorption, reflection, and transmission process. Several ground-based 2D and 3D VLF receiver systems provided complimentary observations of the NAA and natural emissions throughout the flight. For this session, we shall present the first results of the ground based and in situ observations from VIPER, our initial interpretations of those results, and plans for future analysis.