1. CCIR, The Radio Refractive Index: Its Formula and Refractivity Data, Rec. 453-3, RPN Series, Geneva, 1992.
2. Freeman, R. L., Radio System Design for Telecommunications, Chapter 1, John Wiley & Sons, Inc., New York, 1997.
3. Investigation of over-horizon VHF radio signals associated with earthquakes
4. Hall, M. P. M., Propagation of Radio Waves, Chapter 6, The Institution of Electrical Engineers, London, 1996.
5. Hayakawa, M and O. A. Molchanov (eds), Seismo Electromagnetics: Lithosphere-Atmosphere-Ionosphere Coupling, TERRAPUB, Tokyo, 2002.