A Review of Tropospheric Refraction Effects on Earth-To-Satellite Systems

Edward E . Althsuler

Abstract:	Tropospheric refraction effects may seriously limit the performance of communication, navigation and radar systems that operate at low elevation angles. The lower atmosphere has an index of refraction which is slightly larger than unity at the earth's surface and which decreases approximately exponentially with height. As a result, radio waves travel at slower velocity than in free space and as they traverse layers of decreasing index of refraction, they are bent downward. Thus, targets observed from the ground appear to be at higher elevation angle than the true angle and if the range of the target is based on a time delay measurement, the target will appear farther away. In addition, abnormal refractivity gradients may cause radio waves to be trapped within tropospheric layers, thus producing regions through which the waves do not pass: these are called "radio holes". For some locations and for many applications, refractive corrections based on the surface refractivity are adequate for elevation angles above a few degrees. However, new systems which operate at, elevation angles near the horizon often require improved accuracies. In this paper, techniques for obtaining these improved corrections are reviewed.
Published in:	Proceedings of the 16th Annual Precise Time and Time Interval Systems and Applications Meeting November 27 - 29, 1984 NASA Goddard Space Flight Center Greenbelt, Maryland
Pages:	247 - 248
Cite this article:	Althsuler, Edward E ., "A Review of Tropospheric Refraction Effects on Earth-To-Satellite Systems," Proceedings of the 16th Annual Precise Time and Time Interval Systems and Applications Meeting, Greenbelt, Maryland, November 1984, pp. 247-248.
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