Subjects: Astronomy >> Astrophysical processes submitted time 2022-01-14 Cooperative journals: 《天文研究与技术》
Abstract:甚长基线干涉测量(VLBI)通过相位校准(PCAL)信号来校准链路时延。但现有系统的PCAL信号只能获取链路时延的相对变化。而面对UT1精准测量、台站钟差补偿、维护诊断和提升未来深空探测精度等需求,天线链路的绝对时延定标至关重要。在天线链路中,由于存在变频器等器件,绝对时延测量较为困难。本文利用梳状谱相位随频率线性变化的特点,提出了一种不需要参考变频器,采用PCAL信号定标绝对链路群时延的方法。同时,本文设计了一款用于台站快速诊断和绝对时延定标的轻量级PCAL提取软件,该软件目前已在实际调试工作中应用。
Subjects: Astronomy >> Astrophysical processes submitted time 2023-06-07 Cooperative journals: 《天文学进展》
Abstract: As the next-generation VLBI system for geodesy and astrometry, VLBI Global Observing System (VGOS) is able to observe at four frequency bands in the range 2∼14 GHz. Due to the super wide bandwidth of the VGOS system, it is necessary to determine broad#2;band group delay and differential ionospheric total electron content observables simulta#2;neously during the coherent fringe fitting by combining all the bands. In this work, we performed a covariance analysis for evaluating the uncertainties of broadband group delay for VGOS and obtained the uncertainties of group delays for various frequency band combi#2;nations. We also processed the real VGOS observations using fourfit and made a statistical analysis. The results show that the uncertainties derived from covariance analysis agree with those obtained from actual observations, and thus it validates the method that we present#2;ed. This method can be useful for selecting and optimizing frequency sequences for VGOS observations.