Line-of-Sight Paths Over Random Terrain

Very-high frequency radio propagation is often said to resemble optical propagation. A line-of-sight path provides a good radio channel; a path blocked by the terrain does not. With the aid of a topographic map, one can determine whether a path Q1Q2 is a line-of-sight path. Essentially, one must plot the ground elevation profile along the path to see whether the ground intersects the straight line segment Q1Q2. This calculation must include the effect of the earth's curvature. Atmospheric refraction is also accounted for by changing the earth's radius to a fictitious value. Having done the calculation for one path Qi, Q2, we learn little about other paths. The region covered by a transmitter at Q1, i.e., the set of points Q visible from Q1, would be found by plotting ground elevation profiles along views from Qi at every possible azimuth angle. This region might represent the coverage of a TV station or of a base station in a mobile telephone system. This paper analyzes a statistical model to give insight into the way coverage regions depend on properties of the terrain. The parameters 735