深南天球参考框架VLBI观测二十余年回顾：IVS-CRDS (1995-2021)
On More than Two Decades of Celestial Reference Frame VLBI Observations in the Deep South: IVS-CRDS (1995-2021)
AI总结：
本文回顾了1995-2021年IVS-CRDS深南天球参考框架VLBI观测计划的发展，介绍其数据成果，旨在弥补南半球观测不足、提升南天CRF精度，并展望了项目后续改进方向。
摘要：
国际甚长基线干涉测量大地测量与天体测量服务（International VLBI Service for Geodesy & Astrometry, IVS）定期提供高质量数据，用于生成地球定向参数（Earth Orientation Parameters, EOP），以及维护和实现国际地球参考框架（ITRF）与国际天球参考框架（ICRF）。首个射电波段天球参考框架（CRF）版本ICRF1于1997年被国际天文学联合会（IAU）采纳，以取代FK5光学参考框架。此后不久，IVS开始正式运行，到2009年数据量显著增长，足以支撑CRF的第二个版本ICRF2的发布。最新的ICRF3于2018年被IAU采纳。然而，由于观测台站的地理分布集中在北半球，南半球观测数据较少，导致CRF在南天区域的精度普遍较弱。为增加南半球观测数据、提升源的分布密度与测量精度，1995年启动了一系列深南天区观测会话。该项目于2004年正式成为IVS天球参考框架深南天区观测计划（IVS Celestial Reference Frame Deep South, IVS-CRDS）。本文梳理了1995年至2021年间CRDS观测计划的发展历程，详细介绍了其数据产品与研究结果，并总结了这一持续推进的项目即将开展的改进工作。
英文摘要：
The International VLBI Service for Geodesy & Astrometry (IVS) regularly provides high-quality data to produce Earth Orientation Parameters (EOP), and for the maintenance and realization of the International Terrestrial and Celestial Reference Frames, ITRF and ICRF. The first iteration of the celestial reference frame (CRF) at radio wavelengths, the ICRF1, was adopted by the International Astronomical Union (IAU) in 1997 to replace the FK5 optical frame. Soon after, the IVS began official operations and in 2009 there was a significant increase in data sufficient to warrant a second iteration of the CRF, ICRF2. The most recent ICRF3, was adopted by the IAU in 2018. However, due to the geographic distribution of observing stations being concentrated in the Northern hemisphere, CRFs are generally weaker in the South due to there being fewer Southern Hemisphere observations. To increase the Southern Hemisphere observations, and the density, precision of the sources, a series of deep South observing sessions was initiated in 1995. This initiative in 2004 became the IVS Celestial Reference Frame Deep South (IVS-CRDS) observing program. This paper covers the evolution of the CRDS observing program for the period 1995 to 2021, details the data products and results, and concludes with a summary of upcoming improvements to this ongoing project.
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