Tropospheric propagation effects on Earth-space low elevation angle paths

Extensions and reduction of horizon distance were determined for a satellite transmitter under climatologically realistic conditions for refraction in the troposphere. The increase in elevation (grazing) angle was determined under the same conditions. The computations were made, where possible, using parameters available climatologically on a global basis. The effects of normal variations in refractivity, of ducting, and of subrefraction were all considered. Likely limits were placed on the basis of climatology. Examples considered show possible variations in horizon distance from 22 km closer than for a vacuum under extreme conditions of subrefraction to 340 km beyond the free space horizon for an extreme duct condition. Horizon variations due to variations in surface refractivity with normal refraction amount to 109 km. Grazing angle variations between minimum and maximum surface refractivity amount to only about 5 mr, but in a duct they may become as great as 32 mr.