The on-axis beam at Jicamarca: is it pointing correctly?

Abstract

Vertical velocity measurements of atmospheric winds are becoming increasingly important. To obtain the long-term mean vertical motion of the atmosphere is difficult to do, both because of the small velocities involved and because of the finite width of the antenna beam. Since the vertical wind measurement is very sensitive to the tilt of the vertically-directed antenna beam, we decided to get the Jicamarca beam direction by measuring the phase and amplitude of a ref­erence signal at each of the antenna feed points. Our results tell us that, while the antenna pointing direction is already good, there is room for improvement.