The VIPER Sounding Rocket
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. While the VLF penetration process has been modeled and the wave amplitudes measured at the upper bounds of the ionosphere (600-800 km altitude), the actual electrodynamics of the attenuation and propagation process have not been measured from the Earth-ionospheric waveguide, through the ionosphere, and above.
The VLF Trans-Ionospheric Propagation Experiment Rocket (VIPER) rocket will fly a fully 3D electromagnetic field measurement, DC through VLF, and relevant plasma, and neutral particle measurements at mid-latitudes through the radiation fields of an existing VLF transmitter and naturally-occurring lightning in order to explore the following science objectives:
The VLF Trans-Ionospheric Propagation Experiment Rocket (VIPER) rocket will fly a fully 3D electromagnetic field measurement, DC through VLF, and relevant plasma, and neutral particle measurements at mid-latitudes through the radiation fields of an existing VLF transmitter and naturally-occurring lightning in order to explore the following science objectives:
- What is the vertical and horizontal profile of the observed 3D electric and magnetic radiated fields of the VLF transmitter, and how is that profile related to the observed plasma and neutral densities? The observed plasma and neutral density profiles provide the local dielectric tensor and collision frequencies; from the vertical E- and B-field profiles, the reflection, absorption, and transmission processes as a function of altitude can be determined, and thus applied to the broader question of trans-ionospheric escape of terrestrial VLF radiation.
- Are the EM wave properties of lightning radiated fields qualitatively and quantitatively similar to those from the steady-state narrowband VLF transmitter properties, or are there significant differences in apparent reflection, absorption, and transmission that would have significant impacts on the leakage of such VLF sources through the ionosphere?
Our Work
Our group is involved primarily in the modeling of the VLF signals that we expect to measure on VIPER. The amplitude, phase, and frequency response of the trans-ionospheric propagation depends on the state of the ionosphere at the time of the launch; we want to be able to infer the ionospheric state from the measurements. Therefore, we need to be able to predict what we will observe under the full range of possible ionospheric conditions, in order to develop an inversion model. Our forward modeling uses a full-wave electromagnetic model developed by Lehtinen and Inan [2009]. In 2D or 3D coordinates, for a given ionosphere, we can estimate the electric and magnetic wave components at any point in space. By repeating these model calculations for a range of ionospheres, we can develop a picture of what to expect under different conditions.
|
Our group will also provide ground-based measurements of the VLF transmitter and lightning signals, in order to validate the rocket measurements. VLF receivers will be installed at Wallops Island, near the launch site, and in Maine, near the VLF transmitter. The latter receiver will provide a reference for the transmitted amplitude and phase of the NAA transmitter, which is not publicly available. The receiver in Wallops will provide ground-based measurements that can be validated in our full-wave modeling along with the rocket measurements. Together, these measurements will elucidate the propagation of VLF signals by measuring them below and above the ionosphere.
References
- Lehtinen, N. G., & Inan, U. S. (2009). Full‐wave modeling of transionospheric propagation of VLF waves. Geophysical research letters, 36(3).