| Abstract: | We consider some effects of the VHF radio wave propagation in randomly irregular plasma near the Earth. Applications of these effects to main problems of decameter radio astronomy are discussed. In particular, we show that significant measurement errors of about tens to hundreds of percent for the intensity of the VHF radio emission from an extra-terrestrial source may occur due to scattering and focusing/defocusing of the radiation in the ionosphere if VHF radio astronomical facilities operate at middle latitudes. We find that the angular resolution of discrete radio sources observed using radio interferometry and the well-known scintillation methods cannot be better than about a degree due to the effect of the developed ionospheric turbulence. We propose a modified scintillation method based on the spectral analysis of radio emission from discrete sources, which allows the useful high-frequency signal corresponding to diffraction of VHF emission at weak inhomogeneities of interplanetary plasma to be separated against strong, relatively low-frequency fluctuations of the received radiation due to the effect of the developed turbulent structure of the ionosphere. We show that such a method allows the angular resolution of extra-terrestrial radio sources to be improved up to arcsecond level. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 2, pp. 95–105, February 2000. |
