2002ApJ...572..786M

The observed interstellar scintillation pattern of an intraday variable radio source is influenced by its source structure. If the velocity of the interstellar medium responsible for the scattering is comparable to the Earth's, the vector sum of these allows an observer to probe the scintillation pattern of a source in two dimensions and, in turn, to probe two-dimensional source structure on scales comparable to the angular scale of the scintillation pattern, typically ∼10 µas for weak scattering. We review the theory on the extraction of an ``image'' from the scintillation properties of a source and show how the Earth's orbital motion changes a source's observed scintillation properties during the course of a year. The imaging process, which we call Earth-orbit synthesis, requires measurements of the statistical properties of the scintillations at epochs spread throughout the course of a year.