LF AND VLF REFLECTION LOSS IN THE LOWER IONOSPHERE: A THEOREM ON ABSORPTION AND ITS APPLICATION.

Abstract : Two simple practical methods are given for determining the transmission loss of LF and VLF radio waves obliquely reflected from the lower ionosphere in a nuclear burst environment. The constant K, given in RM-4031-PR, is recalculated and found to equal pi, not 2. A theorem, based on full wave theory, is derived that extends results for a nonabsorbing medium to an absorbing medium with minimum complexity. The assumption is made that in the reflecting stratum, the permittivity profile is exponential. At the height where the level of reflection of the upgoing wave is expected to maximize (by the Field-Engel standard), the authors fit an exponential profile and apply to it their analytical expression for attenuation on reflection. Results are corrected as necessary by application of the nondeviating region technique to take account of attenuation below the reflection level. A remarkably accurate alternative method, the phase-integral procedure, combines the two steps. Both methods can be applied with sufficient accuracy for transmission frequencies as low as 10 kHz without use of computers or elaborate codes. (Author)