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Application of an imaging HF riometer for the observation of scintillations of discrete cosmic sources

Scintillations of discrete cosmic radio sources have been investigated theoretically and experimentally for radiation scattered from natural and artificial inhomogeneities in the auroral zone ionosphere. The observations were performed at a frequency of 38.2 MHz with the multibeam phased array antenna of the imaging riometer located at Poker Flat, Alaska. For quiet ionospheric conditions and weak scintillations, the spatial spectrum and transverse motion velocities of the Fresnel inhomogeneities have been recovered. A theoretically based approach has been developed to estimate the time coherence interval of the radiation for the case of saturated scintillations and strong ionospheric turbulence. Examples of scintillation records are analyzed for the case of scattering from artificial ionospheric irregularities induced by high‐power HF radiation from the high‐power auroral simulation (HIPAS) ionospheric modification facility. The effect of aspect‐sensitive scattering of the cosmic source radiation by artificial field‐aligned small‐scale irregularities has been predicted and detected. Prospects for routine observations of the effects of scintillations and aspect‐sensitive scattering are discussed for special operation modes of the ionospheric modification facility.