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ORIGINAL RESEARCH article

Front. Astron. Space Sci.
Sec. Space Physics
Volume 12 - 2025 | doi: 10.3389/fspas.2025.1521497

An Open Source Code for Modeling Radio Wave Propagation in Earth's Ionosphere

Provisionally accepted
Alexander Green Alexander Green 1*William Longley William Longley 2Meers M Oppenheim Meers M Oppenheim 1Matthew Young Matthew Young 3
  • 1 Center for Space Physics, Boston University, Boston, United States
  • 2 Center for Solar-Terrestrial Research, College of Science and Liberal Arts, New Jersey Institute of Technology, Newark, New Jersey, United States
  • 3 University of New Hampshire, Durham, North Carolina, United States

The final, formatted version of the article will be published soon.

    We present FARR (Finite-difference time-domain ARRay), an open source, high-performance, finite-difference time-domain (FDTD) code. FARR is specifically designed for modeling radio wave propagation in collisional, magnetized plasmas like those found in the Earth's ionosphere. The FDTD method directly solves Maxwell's equations and captures all features of electromagnetic propagation, including the effects of polarization and finite-bandwidth wave packets. By solving for all vector field quantities, the code can work in regimes where geometric optics is not applicable. FARR is able to model the complex interaction of electromagnetic waves with multiscale ionospheric irregularities, capturing the effects of scintillation caused by both refractive and diffractive processes. In this paper, we provide a thorough description of the design and features of FARR. We also highlight specific use cases for future work, including coupling to external models for ionospheric densities, quantifying HF/VHF scintillation, and simulating radar backscatter. The code is validated by comparing the simulated wave amplitudes in a slowly changing, magnetized plasma to the predicted amplitudes using the WKB approximation. This test shows good agreement between FARR and the cold plasma dispersion relations for O, X, R, and L modes, while also highlighting key differences from working in the time-domain. Finally, we conclude by comparing the propagation path of an HF pulse reflecting from the bottomside ionosphere. This path compares well to ray tracing simulations, and demonstrates the code's ability to address realistic ionospheric propagation problems.

    Keywords: FDTD, Scintillation, Radio wave propagation, Ionospheric propagation, open source, ionospheric irregularities

    Received: 01 Nov 2024; Accepted: 16 Jan 2025.

    Copyright: © 2025 Green, Longley, Oppenheim and Young. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

    * Correspondence: Alexander Green, Center for Space Physics, Boston University, Boston, United States

    Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.