Challenges in Modeling HF Absorption: Exploring D, E and F-Layer Effects on Signal Attenuation Using Provision of High-frequency Raytracing Laboratory for Propagation studies

Understanding the absorption of high-frequency (HF) radio waves within the ionospheric D, E, and F regions remains a pivotal challenge in accurately modeling signal propagation, particularly when considering ground reflection losses. This study investigates HF signal reception at two HamSCI Personal Space Weather Stations (PSWS): W2NAF near Scranton, Pennsylvania, and KPH in Point Reyes, California. Both stations are equipped with GPS-disciplined Great Radio Amateur Propagation Experiment (GRAPE) receivers that precisely measure standard time signals. Utilizing the PHaRLAP ray tracing MATLAB toolbox alongside the International Reference Ionosphere (IRI)-2020 model, we simulate HF propagation at frequencies of 5, 10, and 15 MHz by launching rays across a spectrum of elevation angles to assess successful transmission paths to each station. A focused analysis on W2NAF aims to discern whether improved signal reception during specific intervals originates from WWV (40.68, 105.04) or WWVH (21.99, 159.77), based on propagation modeling and observed diurnal signal trends. While the PHaRLAP-based model effectively captures overarching absorption patterns, particularly diurnal attenuation profiles at selected UTC times (0, 7, 12, 18, and 20 UTC), it currently lacks detailed treatments of D and E-layer processes and ground reflection losses. Future work will explore the integration of the SAMI3 model within a Python-based workflow to enhance the representation of ionospheric density and dynamics in the E and F regions, acknowledging that SAMI3 does not model the D region. This research endeavors to refine HF propagation modeling by improving absorption estimates across all major ionospheric layers, thereby enhancing our understanding of signal variability and supporting the broader deployment of accessible modeling tools within the ionospheric research community.

We extend our gratitude to Prof. Nathaniel A. Frissell (W2NAF), lead of the Ham Radio Science Citizen Investigation (HamSCI); Prof. Gareth Perry, Assistant Professor, Department of Physics, Center for Solar-Terrestrial Research, New Jersey Institute of Technology; Mr. Gary Mikitin (AF8A), Radio Operators Expert; and Mr. Bill Liles (NQ6Z), HamSCI Community Diversity Recruitment Chair.

We also thank the HamSCI Community, led by The University of Scranton, Department of Physics and Engineering W3USR, in collaboration with Case Western Reserve University W8EDU; the University of Alabama; the New Jersey Institute of Technology, Center for Solar Terrestrial Physics K2MFF; the MIT Haystack Observatory; TAPR; additional collaborating universities and institutions; and volunteer members of the amateur radio and citizen science communities.

This work is supported by the U.S. National Science Foundation Grant AGS-2404997 and Amateur Radio Digital Communications (ARDC).