High resolution measurement of microwave refraction on short tropospheric paths

A method of measuring angle of arrival, or angle of fire, of a microwave signal transmitted over a short line-of-sight path is described. The method used is similar to that employed in conical scan, or simultaneous lobing, radars. Accuracy in angular measurement is achieved by utilizing the portion of the antenna pattern in which the gain function varies rapidly with angle. Using 4-ft aperture antennas operating at 35 GHz on a
6\frac{1}{2}
-mi path, angle of fire is detected linearly with an accuracy of
\pm 0.010\deg
, and the resolution may be as good as
\pm 0.002\deg
. The effects of random atmospheric turbulence on the results is investigated. Many examples of layered structure have been observed, but the most dramatic records come when the atmosphere is unstable and large changes in refraction occur, e.g., at the onset of land and sea breezes.