Radio interferometry is a technique for measuring in-situ electrical properties and for detecting subsurface changes in electrical properties of geologic regions with very low electrical conductivity. Ice-covered terrestrial regions and the lunar surface are typical environments where this method can be applied. The field strengths about a transmitting antenna placed on the surface of such an environment exhibit interference maxima and minima which are characteristic of the subsurface electrical properties.

This paper (Part I) examines the theoretical wave nature of the electromagnetic fields about various types of dipole sources placed on the surface of a low-loss dielectric half-space and two-layer earth. Approximate expressions for the fields have been found using both normal mode analysis and the saddle-point method of integration. The solutions yield a number of important results for the radio interferometry depth-sounding method. The half-space solutions show that the interface modifies the directionality of the antenna. In addition, a regular interference pattern is present in the surface fields about the source. The introduction of a subsurface boundary modifies the surface fields with the interference pattern showing a wide range of possible behaviors. These theoretical results provide a basis for interpreting the experimental results described in Part II.

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