Johnson, Michael D.Narayan, Ramesh2019-09-222016Johnson, Michael D., and Ramesh Narayan. 2016. “THE OPTICS OF REFRACTIVE SUBSTRUCTURE.” The Astrophysical Journal 826 (2): 170. https://doi.org/10.3847/0004-637x/826/2/170.0004-637X1538-4357http://nrs.harvard.edu/urn-3:HUL.InstRepos:41384876Newly recognized effects of refractive scattering in the ionized interstellar medium have broad implications for very long baseline interferometry (VLBI) at extreme angular resolutions. Building upon work by Blandford & Narayan, we present a simplified, geometrical optics framework, which enables rapid, semi-analytic estimates of refractive scattering effects. We show that these estimates exactly reproduce previous results based on a more rigorous statistical formulation. We then derive new expressions for the scattering-induced fluctuations of VLBI observables such as closure phase, and we demonstrate how to calculate the fluctuations for arbitrary quantities of interest using a Monte Carlo technique.en-USJournal Article2019-09-2210.3847/0004-637X/826/2/170