1. Tech. Rept. No. 4312-3;J. J. Angerami,1963
2. Dikshit, S. K., Lalmani, Somayajulu, V. V., and Tantry, B. A. P.: 1971,Indian J. Pure Appl. Phys. 9, 580.
3. Gurnett, D. A., Shawhan, S. D., and Pfeipper, G. W.: 1966,Nature 212, 1442.
4. Haselgrove, J.: 1955, ?Ray Theory and a New Method for Ray Tracing?, London Physical Society Report of Conference on the Physics of the Ionosphere. pp. 355?364.
5. Iwai, A. and Outsu, J.: 1956, ?On the Investigation of Whistling Atmospherics in Japan?,Proc. Res. Inst. Atmos. Nagoya University 4, 29.