Limits to VLBI Resolution Due to Solar Coronal Scattering

Abstract

Electron irregularities in the solar corona scatter the radiation from radio sources. During more than 30 years of coronal electron irregularity investigations, a very complex temporal and spatial behavior of the solar corona have been observed. In particular, the scattering dependence on distance from the Sun varies with both the phase of the cycle and the different solar maxima. The influence of scattering on the highest resolution observations in radio astronomy, i.e., those made with VLBI, is not negligible. It should be taken into account in planning of both the global VLBI as well as the future orbital VLBI stations such as the QUASAT and RADIOASTRON missions. The “normal” scattering dependence on the distance from the Sun is close to the inverse square law, but substantial deviations from this dependence have been found.