The Optical Measuring System of Universal Time: Digital Zenith Tube

Abstract

Universal Time is one of the Earth Orientation Parameters, which reflects the Earth’s rotation. Universal Time is the necessary parameter to build up the connection between the celestial reference frame and the terrestrial reference frame. In present, to measure Universal time relies mainly on Very Long Baseline Interferometry technique, but the period of gaining the observing result is a few weeks later although its measuring accuracy is very high. For shortening the data period and cutting the cost of observations, National Time Service Center constructed the Digital Zenith Tube net. In this paper, we state the structure of Digital Zenith Tube, its observation principle, observing features, observing process, and the system composing of the observing net. The Digital Zenith Tube net can also measure the deflections of the vertical of local stations which is an important parameter in the geodesy.