Institute for Telecommunication Sciences
the research laboratory of the National Telecommunications and Information Administration

J. R. Johler; D. C. Hyovalti

Abstract: Radio navigation systems such as Loran C,D operate on ground waves over distances up to 3000 or 4000 km from the transmitters. If the ground is inhomogeneous and irregular, the wave propagation may be considerably different from the classical smooth, spherical ground behavior. In addition to local perturbations in the field resulting from mountains and ground geological structure, an excess phase accumulation as a function of distance from the transmitter can be theoretically demonstrated. In this paper, the effect of a surface wave, excited by uniform roughness of the ground, on the navigation coordinate calculation is used to calculate large but physically possible excess phase accumulations. A computer program based on simplified and more general rough ground concepts is presented. Time differences, gradients, latitude, longitude, and distances along a geodetic line can be calculated with this program. Various indexes of roughness can be introduced for each propagation path calculated.

Keywords: propagation; LORAN-C; groundwave propagation; ground wave; LORAN; radio navigation; LF ground wave; LORAN D; low frequencies

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