Ionospheric Measurements at Oblique Incidence over Eastern Australia

Abstract

An account is given of night observations of oblique-incidence pulse transmissions on 5.8 Mc/s. over a baseline of 763 km., using a responder technique. The experiment aimed at measuring apparent path lengths as a guide to the identification of the reflecting layer in the ionosphere. The characteristics of beacon triggering are discussed in relation to the echo system received after ionospheric reflection. A correlation of E_s occurrences as observed at oblique incidence and vertical incidence near the midpoint of the trajectory was effected, and certain characteristics of the E_s layer are presented. Unusual records of Pedersen rays are reproduced and sudden height increases and diffuseness of F₂ echoes are discussed. A check on the oblique-incidence theory using a Millington transmission curve on vertical-incidence h'f records yielded reasonable agreement between measured and deduced reflection heights, although there is evidence of a tendency for the predicted obliquity factor to be too low. A rough analysis of oblique-incidence penetrations yielded an average value for the frequency separation of the magneto-ionic M.U.F.'s close to half the gyromagnetic frequency.