1. S. A. Schelkunoff, Electromagnetic waves, D. van Nostrand Company, New York, Chapter 12, (1943).
2. On a method of solving the problem of propagation of electromagnetic waves near the surface of the earth;Leontovič, M.;Bull. Acad. Sci. URSS. S\'{e}r. Phys. [Izvestia Akad. Nauk SSSR],1944
3. Solution of the problem of propagation of electromagnetic waves along the earth’s surface by the method of parabolic equation;Leontovich, M.;Acad. Sci. USSR. J. Phys.,1946
4. On the propagation of radio waves along an imperfect surface;Feinberg, E.;Acad. Sci. USSR. J. Phys.,1944
5. G. Hufford, On the propagation of horizontally polarized waves over irregular terrain, Master’s thesis, University of Washington, 1948.