The increasing accuracy and growing time span of Very Long Baseline Interferometry (VLBI) observations allow the determination of seasonal signals in station positions which still remain unmodelled in conventional analysis approaches. In this study we focus on the impact of the neglected seasonal signals in the station displacement on the celestial reference frame and Earth orientation parameters. We estimate empirical harmonic models for selected stations within a global solution of all suitable VLBI sessions and create mean annual models by stacking yearly time series of station positions which are then entered a priori in the analysis of VLBI observations. Our results reveal that there is no systematic propagation of the seasonal signal into the orientation of celestial reference frame but position changes occur for radio sources observed non-evenly over the year. On the other hand, the omitted seasonal harmonic signal in horizontal station coordinates propagates directly into the Earth rotation parameters causing differences of several tens of microarcseconds.

中文翻译：

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非线性 VLBI 站运动及其对天体参考系和地球方向参数的影响

甚长基线干涉测量 (VLBI) 观测的准确性和时间跨度不断提高，可以确定站点位置的季节性信号，而这些位置在传统分析方法中仍未建模。在这项研究中，我们关注台站位移中被忽略的季节性信号对天体参考系和地球方向参数的影响。我们在所有合适的 VLBI 会话的全球解决方案中估计选定台站的经验谐波模型，并通过堆叠台站位置的年度时间序列来创建平均年度模型，然后在 VLBI 观测分析中先验地输入这些台站位置。我们的结果表明，季节性信号没有系统地传播到天体参考系的方向，但一年中观察到的无线电源的位置发生了不均匀的变化。另一方面，水平站坐标中遗漏的季节性谐波信号直接传播到地球自转参数中，造成几十微角秒的差异。