Probing the ionosphere with pulses from the pulsar B2016+28 at a frequency of 324 MHz

Using ground-space VLBI data from the RadioAstron project archive, the phase distortions of the cross-spectrum caused by the ionosphere have been calculated and their influence on the results of determination of the visibility function has been studied. The Arecibo Observatory’s 300-meter antenna served as the ground station for the interferometer. The separation of ionospheric phase distortions from the influence of the interstellar and interplanetary medium and instrumental errors is based on different frequency dependencies of these effects. The amplitude of ionospheric phase variation caused by electron density fluctuations in the ionosphere above the Arecibo radio telescope is several radians per observation session of about one hour. The structure function of phase variations indicates a continuous spectrum of electron density fluctuations at typical times of 2–5 min with no pronounced signs of quasi-periodic processes. Ionospheric phase fluctuations during pulsar observations increase the width of the maximum of the amplitude of the visibility function as a function of the residual interference frequency by 5–10 mHz with a decrease in the value at the maximum of ≈ 10%. When constructing images of radio galaxies and quasars from ground-based VLBI observations, these phase shifts can significantly distort the final results.