Oblique Incidence Ionospheric Reflections of 100 kHz Pulses

Abstract

The results of a 16‐month study of the phase and amplitude variations of 100‐kHz Loran‐C pulse signals between Attu and Sitkinak in the Aleutian Islands are presented. The data show changes in signal amplitude which occur at the same solar zenith angle throughout the year and phase changes which do not occur at the same solar zenith angle throughout the year. Signal amplitudes averaged 15 dB higher during the night than during the day. The shape of the measured diurnal phase and amplitude changes suppprts a two‐layer formation of the lower ionosphere, the lower layer primarily influencing the signal amplitude, and the other primarily influencing the signal phase. The data suggest that an amplitude change occurs at a solar zenith angle of 100°. This effect occurs while the sun's rays reaching the ionosphere are still penetrating the ozone layer.