Terrain Influences on Effective Ground Conductivity

Measurements of the ground wave field intensity were made along radial paths from a low-frequency transmitter in Rapid City, S. Dak. Ground wave attenuation curves for different conductivities are compared with the measured data. Millington's mixed path theory for path segments with different conductivities is then applied to obtain a ground conductivity map. Effects of topological features such as hills, ridges, and rivers, and variations in ground moisture and temperature are discussed. Hills and ridges are described along each radial path for the purpose of indicating the influence of terrain irregularities. The conductivity variations have an impact on radio station coverage which is described for a low-frequency range station.