Statistical Variations in the Apparent Specular Component of Ionospherically Reflected Radio Waves

Abstract

The specular component of an ionospherically reflected radio wave giving highly correlated signals between elements of an array of antennas is measured and found to vary in a way suggesting that it is Rayleigh distributed. Examples illustrating the rate at which variations occur are given and it becomes clear why averages over different periods may give quite dissimilar results. It is inferred that there is, strictly speaking, no specular component but a group of rays all coming from very similar directions.

A Survey of HF Interferometry for Ionospheric Propagation Research

“…Coherence ratio measurements with 20 to 60 second time averaging are more frequently reported. More recently 1 to 10 second average coherence ratios have been measured at SwRI with the computer instrumented interferometer and by Boys [1968] using the more powerful sampling array technique. For mode 1, azimuth is 336.7 ø and elevation is 13.0ø; for mode 2 The results of a dynamic wave interference simulation at this laboratory (two-mode source with statistical mode scintillation greater than ñ15 db) showed that mode amplitude and phase must be simultaneously in phase with < 10-db amplitude ratio for accurate mode resolution.…”

“…Most recently, interference field measurements have utilized sampling arrays and non plane wave analysis of the ionospheric source in estimating mode directions [Gething et al, 1969;Burtnyk et al, 1964;Burtnyk and Wol[, 1967] and coherence ratio [Boys, 1968].…”

Small‐Aperture Measurements of the Shape of the Received Cone of Rays in Long‐Distance Ionospheric Propagation

“…The same type of technique was used by Boys [1968], but the 'wave-normal' directions that he observed were averaged over a large area (80 square wavelengths) and represented mean values. It was, however, demonstrated that the fluctuations in the actual wave-normal direction were almost uncorrelated within about 50 meters even for signals that appeared to be highly coherent over this distance.…”