Propagation of an electromagnetic pulse from a nuclear burst

Abstract

The general study of nuclear detection clearly identifies the theoretical problem of predicting the effect of the propagation medium on the form or shape of the low-frequency electromagnetic pulse of nuclear origin propagated to great distance in the terrestrial waveguide. This is accomplished with a theory of propagation into which an arbitrary electron density profile of the ionosphere can be introduced using a quite general cold magnetoplasma theory. In a previous paper by the author, the propagation of the ground wave electromagnetic pulse was discussed in detail and the engineering significance of the propagation theory, to nuclear detection systems was considered quantitatively. At distances from the source greater than approximately 100 km, the ionosphere reflections become an important consideration. The theory of propagation for ionospheric waves is introduced into the analysis in this paper. A transient waveform reconstructed theoretically at great distance from the source can be analyzed in the time domain with the aid of a geometric series expansion of the solution in the space domain. Thus, different times on the propagated pulse can be identified with particular reflection regions of the ground and ionosphere along the propagation path. In the geometric-optical limit, the individual ionospheric waves correspond approximately to rays traveling to and fro between the ionosphere and the ground, and the composite pulse at great distance can be considered to be a superposition of a multiplicity of pulses, each pulse delayed in time by the delay time of the ray.