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4. V. S. Beley, V. G. Galushko, and Yu. M. Yampolski, “Traveling Ionospheric Disturbances Diagnostics Using HF Signal Trajectory Parameter Variations,” Radio Sci. 30(6), 1739–1752 (1995).
5. K. Davies, Ionospheric Radio, (Peter Peregrinus, London, 1990).