International Celestial Reference Frame (ICRF-3)

天体测量射电源目录，特别是国际天体参考系（ICRF）代表了准惯性天体参考系最准确和最稳定的实现。虽然以前的icrf是由所有可用的全球S/ x波段观测组成的单一VLBI解决方案，但新的（第三）框架，ICRF-3，将在未来几年内应国际天文学联合会（IAU）的要求编制，将是一个组合的多频率目录。原因是目前NASA/JPL的X/ ka波段观测的竞争性解决方案是可用的，它将与S/X波段观测的多个解决方案相结合。该项目是在1503研究单位“监测全球变化和空间精确导航的时空参考系统”的框架内申请的，它将为合并多个目录制定必要的方法和程序。新的方法是使用观测值的最小二乘解的中间结果，即普通方程系统，而不是源位置本身。这种方法首次允许将全部方差-协方差信息转移到最终目录。此外，不稳定源的参数化可以在关键研究后适当的地方引入线性样条。为了使组合正常工作，即不引入帧约束和其他畸变，输入法向方程组必须不受基准约束或必须使其无基准约束。在该项目中，最终的ICRF-3目录将与国际天文学联合会第三次实现国际天体参考框架工作组密切合作编写。

Astrometric radio source catalogs in general and the International Celestial Reference Frame (ICRF) in particular represent the most accurate and most stable realizations of a quasi-inertial celestial reference system. While previous ICRFs were composed of a single VLBI solution of all available global S/X-band observations, the new (third) frame, ICRF-3, to be compiled in the next few years on request of the International Astronomical Union (IAU), will be a combined multi-frequency catalog. The reason is that by now a competitive solution of X/Ka-band observations from NASA/JPL is available, which will be combined with multiple solutions of S/X-band observations. The project, which is applied for in the framework of the Research Unit 1503 "Space-Time Reference Systems for Monitoring Global Change and for Precise Navigation in Space", will develop the necessary methods and procedures for the combination of multiple catalogs. New is the approach of using intermediate results of the least squares solutions of the observations namely normal equation systems instead of the source positions themselves. This method permits for the first time the transfer of the full variance-covariance information to the final catalog. Furthermore, the parameterization of unstable sources may be refined introducing linear splines where deemed appropriate following critical investigations. For the combination to work properly, i.e., without introducing frame constraints and other distortions, the input normal equation systems have to be free of datum constraints or have to be made datum-free. In the project, the final ICRF-3 catalog will be compiled in close collaboration with the IAU Working Group on the Third Realization of the International Celestial Reference Frame.