SUMMERY

We have analysed the literature suggestions regarding possible changes in vertical magnetic transfer function (VTF) over time. We have shown that for periods above 1500 s the observed changes in VTF are caused by the source effect and we proposed how to reduce this negative impact. For calculations we used 1-min recordings of geomagnetic variations registered between 2002 and 2017 in various geomagnetic observatories. In data processing we used frequency-domain Egbert's algorithm and our original algorithm based on the method of least squares in the time domain for some comparisons and tests. We have shown that for periods over 1500 s the VTFs calculated separately from summer and winter data are different. However, our analysis shows that the variability of the VTF values obtained is misleading and results from time-changing presence of magnetic field variations that do not fulfill the assumption of plane wave (there is a vertical component in the incident magnetic field). These variations are much more numerous in summer than in winter. More detailed analysis has shown also that they are usually small at night and big during the day. The vertical components of these variations constitute an error correlated with input signals (horizontal components), which alters the values of the determined VTF. Furthermore, error bars do not take this effect into account. It makes it impossible to improve the accuracy of calculations by increasing the amount of data. Analysing the estimated external parts of vertical components from the Central European observatories we noticed a great similarity of these signals even if the induction components were clearly different, which indicates that this is a regional effect. On this basis, we proposed a procedure to improve the accuracy of VTF determination by means of pre-selection of data.

中文翻译：

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可靠估计地磁传递函数的源效应降低

总结

我们分析了有关垂直磁传递函数（VTF）随时间可能变化的文献建议。我们已经表明，对于1500 s以上的时间段，观察到的VTF变化是由源效应引起的，我们提出了如何减少这种负面影响的方法。为了进行计算，我们使用了2002年至2017年在各个地磁观测站记录的1分钟地磁变化记录。在数据处理中，我们使用了频域Egbert算法和基于时域最小二乘法的原始算法进行一些比较和测试。我们已经表明，对于1500 s以上的时间段，与夏季和冬季数据分别计算出的VTF是不同的。然而，我们的分析表明，所获得的VTF值的可变性具有误导性，是由于不满足平面波假设（入射磁场中存在垂直分量）的磁场变化随时间变化而导致的。这些变化在夏天比冬天更多。更详细的分析还表明，它们通常在晚上很小，在白天很大。这些变化的垂直分量构成与输入信号相关的误差（水平分量），从而改变确定的VTF的值。此外，误差线没有考虑到这种影响。通过增加数据量无法提高计算的准确性。分析来自中欧天文台的垂直分量的估计外部部分，我们发现这些信号有很大的相似性，即使感应分量明显不同，这表明这是区域性影响。在此基础上，我们提出了一种通过数据预选来提高VTF确定准确性的程序。