The diffraction of satellite signals by isolated ionospheric irregularities

Abstract

Procedures are given for the rapid calculation of refraction and diffraction patterns produced by isolated ionospheric irregularities. These patterns are observed experimentally, and a sensitive polarisation angle recorder is also used to determine the associated changes in electron content. Large scale irregularities in the F-region are shown to cause variations of several decibels in the amplitude of 20 and 40 MHz satellite signals. Dense, isolated irregularities produce patches of ‘scintillations’ on 20 MHz. The common assumption that scintillations are caused by a large number of small irregularities, acting as a random diffracting screen, is therefore incorrect on many occasions. Small isolated irregularities produce diffraction patterns which depend only on the total number of electrons in the irregularity, and the height. Irregularities of all sizes commonly occur in trains; in such cases the height of the irregularities can be determined by comparing the depth of the fluctuations in amplitude and in polarisation. Calculated heights are mostly in or above the F-region. For large isolated irregularities, their position with respect to the peak of the F-layer can be obtained directly from the different times at which amplitude fluctuations occur on 20 and 40 MHz.