Extremely Low Frequency (ELF) Ionospheric Radio Propagation Studies Using Natural Sources

The purpose of this paper is to describe methods of studying the propagation of radio waves over the earth\´s surface in the extremely low frequency (ELF) frequency band (3 Hz-3 kHz) using natural (as distinct from "man-made") sources of radiation. Attention is focused on the characteristics of the radio wave field and on methods of analysis of acquired data in order to obtain information on propagation parameters of interest in Project Sanguine. Wave impedance measurements are identified as being of particular importance in these investigations.