The secular aberration drift observed as the apparent proper motion of extragalactic radio sources is caused by the acceleration of the coordinate origin,the Solar System barycenter.So,the acceleration can be estimated as a global parameter by using the 30 years global geodetic/astrometric VLBI data.This estimation is independent of any kinematic or dynamic model of the Milky Way or statistics hypothesis.The estimated acceleration in the direction of the Galactic center is (0.80±0.04) cm·s-1 ·yr-1,while the other two components are (0.0-1±0.06) and (0.52±0.05) cm ·s-1 ·yr-1 in the direction along the Solar motion in the Galactic plane and in the direction normal to the Galactic plane,respectively.The estimate of the acceleration independently provides another kinematics parameter without referring to any objects within the Galaxy.
首先对IVS(International VLBI Service for Astrometry and Geodesy)UT1加强观测的历史发展和总体情况进行了比较详细的介绍,对目前加强观测中存在的问题进行了比较全面的分析;在此基础上对IVS从1984年2月到2011年8月全部的加强观测数据进行了综合处理,进一步分析了加强观测解算UT1的历史改进和目前的解算能力,对比分析不同类型加强观测的UT1结果,发现不同观测网之间存在数十微秒水平的差异;并着重分析了上海佘山站参与的加强观测的解算结果,分析表明上海佘山站在IVS加强观测中与其他参与台站具有相同的测量能力.总体而言,目前IVS加强观测确定的UT1与IERS(International Earth Rotaion Service)C04之间存在约10μs水平的不确定性.
Prior to achieving high precision navigation of a spacecraft using X-ray observations, a pulsar rotation model must be built and analysis of the precise posi- tion of the Earth should be performed using ground pulsar timing observations. We can simulate time-of-arrival ground observation data close to actual observed values before using pulsar timing observation data. Considering the correlation between the Earth＇s position and its short arc section of an orbit, we use polynomial regression to build the correlation. Regression coefficients can be calculated using the least square method, and a coordinate component series can also be obtained; that is, we can calcu- late Earth＇s position in the Barycentric Celestial Reference System according to pulse arrival time data and a precise pulsar rotation model. In order to set appropriate param- eters before the actual timing observations for Earth positioning, we can calculate the influence of the spatial distribution of pulsars on errors in the positioning result and the influence of error source variation on positioning by simulation. It is significant that the threshold values of the observation and systematic errors can be established before an actual observation occurs; namely, we can determine the observation mode with small errors and reject the observed data with big errors, thus improving the positioning result.
Feng Tian 1,2,Zheng-Hong Tang 1,Qing-Zeng Yan 1,2 and Yong Yu 11 Shanghai Astronomical Observatory,Chinese Academy of Sciences,Shanghai 200030,China
