An Investigation of HF Auroral Backscatter over a Bistatic Path.

Abstract : A Wullenweber antenna array was used to record stepped-frequency ionograms over a bistatic path including an auroral reflection. Energy was transmitted northward from Rome, New York. Ionograms were recorded near Urbana, Illinois at stepped-azimuth intervals over a northerly sector. The ionograms were analyzed to determine the statistical occurence of auroral backscatter as a function of azimuth and time delay. These data were compared with theoretical results based upon a specular reflection from an auroral curtain. A technique was developed to locate the reflection point from the time delay, azimuth and maximum frequency of a stepped-frequency auroral backscatter trace. Maps were constructed showing regions of maximum frequency of occurrence of HF auroral backscatter. Results show an equatorward shift of the backscatter region with increasing magnetic activity and suggest that reflecting surfaces are horizontally elongated along lines of constant magnetic inclination. (Author)