Studies of ionospheric forward scattering using measurements of energy distribution in azimuth

Abstract

Measurements of phase and amplitude have been carried out on signals on 37Mc/s received from a transmitter at Gibraltar. The receiving sites were at Slough and Castlemartin, which are each about 1740km from Gibraltar, and were equipped with pairs of aerials whose spacing could be varied from λ to 10λ. The results were not consistent with the idea that the forward-scattered signal was due to the combination of many randomly-phased radio waves. Frequently one signal appeared to be dominant, as might be expected if reflections from meteor trails formed an important part of the resultant signal. The calculation of an azimuth power distribution on the basis of phase measurements with different aerial spacings then becomes of uncertain validity. Some results obtained in this way are presented, but reliance is placed mainly on work with a small, fixed aerial spacing. This shows a marked diurnal variation of mean bearing; at Slough for most of the year it is on average 7°W of the Gibraltar bearing by night but 0°W by day. A comparison with observations at Castlemartin in Wales suggests that the scattering process is due almost entirely to meteor reflections by night but that during the day there is also present a component due to turbulent scattering which contributes rather more than half the total energy.