An investigation has been made of the degree to which the invariance of the relative dispersion of the atmosphere will permit an interferometric separation between geometric path differences and path differences due to atmospheric inhomogeneities. Humidity variations are the most serious. A difference in average humidity of 1% of saturation at 15°C would affect the comparison of two paths by approximately 2 parts in 10<sup>8</sup>. The feasibility of photographing interference for long paths through an uncontrolled atmosphere has been investigated. Photographs of channel spectrum interference have been readily obtained for path lengths of 115 m near ground level.
KENT E. ERICKSON, "Long-Path Interferometry through an Uncontrolled Atmosphere," J. Opt. Soc. Am. 52, 781-786 (1962)