UT1 measurement and accuracy analysis based on digital zenith telescope

Universal time(UT1) is an alternative description of the Earth's rotation angle, essentially one of the spatial parameter representing Earth's orientation , which reflecting subtle changes in its rotational speed. Recently, while very long baseline interferometry(VLBI) achieves high-precision measure-ments 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. This study briefly introduces the digital zenith telescope measurement system, basic principles of UT1 measurement, and data processing. Based on more than 400 UT1 measurement experiments conducted at the Luonan, Lijiang and Delingha, the measurement accuracy of UT1 based on digital zenith telescope was analyzed. The experimental results show that the internal consistency accuracy within 20 minutes can reach 10 milliseconds, and the internal consistency accuracy of single-day observation can reach 0.05 arcsecond. Compared with IERS 14C04, the mean absolute error of UT1 measurement is approximately 3 milliseconds. 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, particularly functioning as an emergency backup when satellite navigation fails.