A theoretical study of errors in radio interferometer type measurements attributable to inhomogeneities of the medium

The effects of the variation of the index of refraction of the earth's atmosphere on the angular information yielded by radio interferometers for terrestrial and near-terrestrial sources are investigated, and a second-order correction is derived. Numerical values are not given since, in general, they require the use of high-speed computers to integrate the error term over the index of refraction profile; however, for various special “models,” this need can be circumvented. One such case, the “flat-earth free-space” model is treated, both to serve as a check on the mathematical derivations, since it can be solved directly, and to give some idea of the size of the expected error.