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Horizon Focusing Effects Observed on Ionospherically Reflected Radio Waves
Author(s) -
Humphrey L. C.
Publication year - 1968
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1002/rds19683111074
Subject(s) - ionosphere , physics , caustic (mathematics) , curvature , transmitter , optics , elevation (ballistics) , concentric , computational physics , radio wave , geometry , geophysics , mathematics , telecommunications , astronomy , computer science , channel (broadcasting) , quantum mechanics , mathematical physics
The focusing gain parameters associated with radio waves reflected obliquely from the ionosphere as derived theoretically are compared with experimental observations. The description of the field in the neighborhood of the caustic depends on the shape of the ionosphere with respect to the earth. For an ionosphere concentric with the earth and a surface location transmitter it is convenient to describe the focusing gain in terms of the evaluation angle of arrival. For a tilted ionosphere, or for an elevated transmitter in which the caustic is elevated above the earth's surface, it is convenient to describe the field as a function of the distance behind the cusp, and above the caustic surface. Experimental observations indicate both situations may exist in nature. The concentric ionosphere is termed the normal situation, and a gain inversely proportional to the approximate cube of the elevation angle was indicated by the experimental data as opposed to a straight inverse relationship by geometric optics. The effect of a distorted ionosphere was evidenced by strong focusing gain at positive elevation angles. It is hypothesized that an increase in curvature of the ionosphere can result in the observed gains which would be consistent with the theory. The required curvature has been observed on other experimental programs.