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.