Radio-star visibility fades in Alaska near Solar Minimum

Abstract

Quantitative results for 49 visibility fades observed from College, Alaska, during 1965 are presented. A majority of the fades revealed ionospheric optical depths in excess of unity at 68 MHz. Optical depth is numerically equal to mean‐square fluctuation in radio‐frequency phase across a plane at the base of the scattering region; thus, the fades often were characterized by rms phase deviations in excess of one radian at 68 MHz. The wavefront phase structure immediately after scattering was found to have scales in the range of tens and hundreds of meters. The observations usually were not consistent with the demands of a Gaussian autocorrelation function, as is commonly assumed. Rather, the perturbed wavefronts displayed evidence of quasi‐periodic structure in the observed dimensional range.

A Proposed Wide‐Band Satellite Transmission Experiment

“…sional nearly complete loss of signal correlation between sufficiently separated antenna elements; this phenomenon would limit the achievable angular resolution of the antenna. Such occurrences have been observed at VHF through the equatorial ionosphere [Koster, 1958;Coates and Golden, 1968] and at VHF and UHF through the auroral ionosphere [Little et al, 1962;Flood, 1963;Fremouw and Lansinger, 1968]. At higher frequencies, partial decorrelation across a large-aperture antenna may occur; this decorrelation would lead to reduced performance.…”

Measurement of phase variance and autocorrelation during radio-star visibility fades

“…It is the purpose of this paper to present an experimental method for determining the variance and autocorrelation of phase at the base of the ionosphere from visibility-fade observations at the ground. The approach is through the graphical relation between A from College, Alaska, has been prepared as a companion paper [Fremouw and Lansinger, 1968]. Additional details of experimental procedure, including error analysis, may be found in a report by Fremouw [1966].…”