Analysis of Astrometry Accuracy Considering Effects of Bulletin A

Earth orientation parameters (EOP) is of very importance to astronomical data calculation and its accuracy affects the final positioning and orientation. At present, there is no technical means to obtain high-precision EOP observation value in real time, which mainly relies on the Bulletin A forecast issued by the International Earth Rotation and Reference Systems Service (IERS). However, there is still lack of systematic research on how it affects astronomical measurement. To this end, the long-term variation of forecast error and the variation of forecast error for different time spans from 1 to 365 days are studied for a period of 1998—2018. Taking the observation data of a digital zenith telescope as an example, the influence of forecast error on astronomical measurement is analyzed. It shows that the influence of polar motion forecast for 365 days on astronomical longitude is less than 0.03 as, on latitude less than 0.09 as, and on astronomical azimuth less than 0.07 as, showing that it outperforms the precision requirement of first order astrometry. UT1−UTC (universal time1−universal time coordinated) forecast accuracy is the main factor limiting A bulletin accuracy. The forecast accuracy of the UT1−UTC is the main factor limiting the accuracy of the Bulletin A, and the error of its prediction over 40 days can not meet the minimum requirements of the first order astrometry, and the prediction accuracy of the UT1−UTC still needs to be further improved.