1962—1988年我国综合世界时的均匀化

A HOMOGENEOUS UT1-UTC SERIES OF CHINESE JOINT SYSTEM FROM 1962 TO 1988

本文讨论并给出1962—1988年期间我国综合世界时均匀化所要加的修正.其中光行差常数变化对我国综合世界时的影响主要是幅度约1.7毫秒的常数项;FK5-FK4星表系统差的影响表现为平均幅度约—0.7毫秒的常数项和平均振幅为1.7毫秒的周年项;章动模式变化影响的周年振幅在0.5—1.5毫秒之间,受章动长周期项制约。比较表明,由于FK5-FK4星表系统差影响中的常数项,使均匀化以后的我国综合世界时对于国际时间局B87C02序列的年平均偏离较之均匀化以前的相应结果略有增大,但大多数年份的均方波动都减小了.

Chinese Joint universal time System (CJS) was established in 1959. During past 30 years, different systems of astronomical constants and star catalogues were used in reduction of UT1-UTC series of CJS. For example, FK4 catalogue was used in CJS during 1962--1983 while new aberration constant K=20~″.496 was used during 1973--1983. Although qusi-FK5 system and IAU 1980 nutaton series were used in reduction of the optical observations after 1984.0, UT1-UTC of CJS still remained in the old system. The reason is that the changes of observations were treated as systematic difference of instrument with respect to the system of CJS. It is of great benefit for the users both in geodesy and astrometry to homogenize UT1-UTC of CJS in new system based on FK5 catalogue, IAU 1976 precession constant and IAU 1980 nutation series. Caused by the systematic difference FK5-FK4 in star positions and proper motions, the change of nutation model from Woolard's to Wahr's series (both for 1962—1988) and of aberration constant K from 20~″.47 to 20~″.496 (for 1962--1972), three kinds of corrections for the influence on UT1-UTC of CJS were calculated. Fig. 1 shows the correction which were added to UT1-UTC of CJS and caused by the systematic difference FKS-FK4. It is clear that the correction contains a constant term of about--0.7 ms, an annual term of about 1.7 ms and a small semiannual term of about 0.4 ms in average amplitude. Fig. 2 plots the correction caused by the change of nutation model. It is also clear that the correction consists of both annual and semi-annual terms about 0.8 ms and 0.2ms in average amplitude, and the total amplitude of the periodic terms appears in about 18.6 year term. Fig. 3 shows the correction for the change of aberration constant K. The correction is a constant term of about 1.7 ms on an average and small periodic terms with amplitudes less than 0.5 ms in total. Comparison is made between the homogeneous series of UT1-UTC of CJS (based on both FK4 and FK5 systems) and UT1-UTC series of ERP (BIH) 87C02. Yearly mean values and RMS of the deviations are shown in Table 1 and Fig. 4.