surveying iii (topographic and geodetic surveys) - Modern Prepper

Table 2-1. Correction for the Earth's Curvature and Refractionc. The general problem for intervisibility is determining how much a line of sight between twostations will clear or fail to clear an intervening obstruction. Use the following formula to make thisdetermination:h = The elevation of the line at obstruction (in meters)h1 = The elevation of the lower station (in meters)h2 = The elevation of the higher station (in meters)d1 = The distance from the lower station to the obstruction (in kilometers)d2 = The distance from the higher station to the obstruction (in kilometers)The first two terms of the above formula are a solution of similar triangles. The last term is thecurvature and refraction correction. If the two stations are at the same elevation, the obstruction can becleared using signals of equal height, and the above formula becomes the following simple formula:h = hl - 0.0676 d1d2The height of the signal at each end becomes the following formula:h1 = h + 0.0676 d1d2d. For a given length (K) between stations, the elevation required at one station to see the otherstation across a level surface (such as water) is K2 X 0.0676. If both stations are raised to the sameelevation, the height (h2,1) required at each2-31 EN0593