Warrington, E. Michael, Alain Bourdillon, Eulalia Benito, Cesidio Bianchi, Jean-Philippe Monilié, Martha Muriuki, Marco Pietrella, et al. 2009. “Aspects of HF Radio Propagation”. Annals of Geophysics 52 (3-4): 301-21. https://doi.org/10.4401/ag-4577.