Accuracy analysis of UT1 measurement based on a digital zenith telescope

Universal time (UT1) is an alternative description of the Earth’s rotation angle and is one of the spatial parameters representing the Earth’s orientation that reflects subtle changes in its rotational speed. While very long baseline interferometry (VLBI) has recently achieved high-precision measurements of UT1, its prohibitively high equipment costs and complex data processes make it difficult to meet the requirements of users in fields with stringent real-time data requirements, such as astronomical measurement and celestial navigation. Currently, the digital zenith telescope is one of the most accurate ground-based optical astronomical measurement instruments available. This study briefly introduces the digital zenith telescope measurement system and the basic principles of UT1 measurement and data processing. On the basis of more than 400 UT1 measurement experiments conducted at Luonan, Lijiang, and Delingha, the accuracy of UT1 measurements based on the digital zenith telescope is analyzed. The experimental results show that the internal consistency accuracy within 20 min can reach 10 ms and that the internal consistency accuracy of single-day observations can reach 0.05 arcsec. Compared with IERS 14C04, the mean absolute error of the UT1 measurements is approximately 3 ms. This indicates that optical astronomical observations based on the digital zenith telescope can be used as an effective regional autonomous monitoring method to supplement VLBI by providing high-frequency UT1, functioning in particular as an emergency backup when satellite navigation fails.