Computer Science
Scientific paper
Oct 1961
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1961saosr..76.....g&link_type=abstract
SAO Special Report #76 (1961)
Computer Science
1
Scientific paper
A theoretical analysis of the effects of the ionosphere on HF observations from satellite-borne radio telescopes is presented. The primary effect investigated is the focusing effect of the ionosphere on incoming cosmic noise. This effect was computed according to the Hamiltonian equations for a ray path in a general magnetoionic medium, assuming the ionosphere to be a nonhomogenous, nonisotropic, magnetoionic medium analogous to a spherical shell lens. The electron-density profile used was derived from averages of IGY data, and the earth's magnetic field was assumed to be dipole in nature. The numerical procedures involved were programmed for an IBM 7090 computer. The rays were computed and plotted for sources located at infinity and frequencies in the Band 1 to 30 mc/sec. In the search for focal regions, only those ionospheric irregularities and discontinuties that were larger than the wavelengths used were considered. Basic consideration was given to refraction, reflection, and resulting focusing effects for frequencies higher and lower than critical and for satellites in conjunction and in opposition with respect to the source and the earth. Extended focal regions were found along the line containing the center of the earth and the Source in opposition. When the source was considered extended, the calculated situation of opposition was found to contradict the common belief that the ionosphere would create a shadow. However, it is noted that a satelliteborne radio telescope located at a point of the focal region will not experience continuous intensified reception of the cosmic radio background. Because of the multipath structure of ionospheric propagation, alternating maxima and minima of the intensity received should be observed. The geometric gain of the ionosphere was calculated by again assuming the ionosphere to be analogous (at radio frequencies) to a spherical shell lens. In cases of special interest, the equivalent aperture of the ionosphere was computed with the observing satellites located at the focal region.
Grossi Mario D.
Strom Karen M.
Strom Stephen E.
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