Radio Horizon
Radio Horizon : The locus of points at which direct rays from a radio transmitter become tangential to the earth's surface. The radio horizon extends beyond (below) the geometrical and visible horizons as the result of normal atmospheric refraction. It may be decreased or increased in particular cases as standard propagation is replaced by substandard propagation or superstandard propagation, respectively. Beyond the radio horizon, surface targets cannot be detected under normal atmospheric conditions although significant amounts of radio power have been detected in the diffraction zone below the horizon. It is now felt that this represents power scattered by turbulence-produced atmospheric inhomogeneities. Assuming a smooth surface, the distance of the horizon is given approximately by the equation: R = flh where R is the distance in statute miles and h is the height, in feet, of the radar antenna above the surface. See: Effective Earth Radius, Scatter Propagation. N.B. Refer to source to verify equation(s)
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