Journal of Atmospheric and Terrestrial Physics
On the variation of radio star and satellite scintillations with zenith angle
Abstract
The theory of the variation of the depth of amplitude scintillations with the zenith angle of the source is considered, for radio waves received from a star or a satellite. It is assumed that irregular phase fluctuations are impressed on the wave in travelling through the ionosphere, and that the amplitude fluctuations develop by a diffraction process as the wave propagates in the free space beneath the ionosphere. Two effects are produced by an increase in the zenith angle of the source. The magnitude of the phase perturbations increases, because the thickness of the ionosphere along the line of sight increases, and the geometry of the diffraction process changes. Theoretical results are given, both for Isotropic irregularities and for irregularities elongated along the direction of the earth's magnetic field. The advantages of observing simultaneously on two wavelengths are stressed. Some comparisons with available experimental data are made, and suggestions are made for future experiments. Irregularities at different distances from the observer are not equally effective in producing amplitude scintillations, and some examples of the “weighting function” which determines their effectiveness are given. Various measures of “scintillation depth” are discussed and related to each other.
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