Inversion Methods for Earth's Radiation Belt Observations from the Moon Using Cyclo-synchrotron emissions

Energetic electrons in Earth’s radiation belts emit cyclo-synchrotron radiation as they are deflected by the planet’s magnetic field. These emissions provide valuable insights into the spatial and energy distributions of trapped electrons and their dynamic behavior over time. However, because this radiation occurs at frequencies below 10 MHz, it is blocked by the ionosphere, making direct observation from Earth impossible. Current in situ satellite measurements offer critical data but are limited in spatial and temporal coverage, leaving significant gaps in our understanding of radiation belt dynamics. Observations of the cyclo-synchrotron emission from the Moon’s near side could offer a unique position for real-time monitoring of radiation belts activity.

Given the typical energies of radiation belts electrons (10 keV - 1 MeV), the emitted signal follows the cyclo-synchrotron formalism. ONERA has developed a cyclo-synchrotron radiation simulator that uses the electron distributions from the physics-based Salammbô model [Marc et al., 2024].

Here, we present the development of inversion methods to retrieve the 3D distribution of electrons (Kinetic energy, Equatorial pitch angle, Roeder’s parameter L*) from simulated images of the cyclo-synchrotron radiation. A PCA-based approach demonstrates highly promising results, confirming the technical feasibility of this method and its potential to enhance our understanding of radiation belt dynamics.

With future lunar missions expected to deploy instruments capable of capturing 2D images of these emissions, developing robust inversion techniques will be essential to maximize the scientific return of these observations and enhance our space weather capabilities.