Differential angle of arrival: Theory, evaluation, and measurement feasibility

The problem of measuring differential angle of arrival through two relatively small apertures of variable separation is considered. The motivation is to evaluate the practicality of a measurement program using such a quantity to observe atmospheric turbulence wavefront distortion effects when one end of the link is moving and cannot be tracked precisely. (If precise tracking were possible, then measurement of the angular resolution with a single aperture could be used to characterize the propagation path.) Theoretical results for the mean-square difference in angle of arrival are developed and numerical results are presented. Comparison of expected magnitude of effects with available measurement instrument precision indicates that the experiment should be possible, but will depend on our ability to achieve an rms single-axis angle-of-arrival measurement precision of the order of 0.1 arc sec or better.