Surface wave propagation over a rough talus slope at 160 MHz

Field experiments of air surface wave propagation at 160 MHz were performed on a rough non-conductive dielectric talus slope of granite blocks, all of the same composition. Amplitudes for both vertical and cross polarization were measured meter by meter along linear transects 250 and 500 m long, along with GPS measurements of position and elevation. Attenuation rates for both polarizations were greater for smoother transects, with height standard deviation of about one third free space wavelength, than for rougher transects with up to one wavelength deviation. This unexpected finding resulted from the smoother dielectric surfaces permitting loss of energy into subsurface head waves, as evidenced by the nearly range-squared dependency of the surface waves. The results suggest direct point-to-point communications over rough terrain can be realized over multi-km distances.