Radio Horizon

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Radio Horizon

The locus of points at which direct rays from a radio transmitter become tangential to the earth's surface. Assuming a smooth surface, the distance of the horizon is given approximately by the equation

Missing Image:img src="SP7_r_files/radhoriz.gif"

where r is the distance, statute miles, and h is the height, feet, of the antenna above the surface. See effective radius of the earth, scatter propagation. Compare radar horizon. </dd>
The 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. [[/a>|/a> ]]


This article is based on NASA's Dictionary of Technical Terms for Aerospace Use