One of the main tasks of Very Long Baseline Interferometry (VLBI) is the rapid determination of the highly variable Earth’s rotation expressed through the difference between Universal Time UT1 and Coordinated Universal Time UTC (dUT1). For this reason, dedicated one hour, single baseline sessions, called “Intensives”, are observed on a daily basis. Thus far, the optimal geometry of Intensive sessions was understood to include a long east–west extension of the baseline to ensure a dUT1 estimation with highest accuracy. In this publication, we prove that long east–west baselines are the best choice only for certain lengths and orientations. In this respect, optimal orientations may even require significant inclination of the baseline with respect to the equatorial plane. The basis of these findings is a simulation study with subsequent investigations in the partial derivatives of the observed group delays \(\tau \) with respect to dUT1 \(\partial \tau /\partial dUT1\). Almost 3000 baselines between artificial stations located on a regular \(10 \times 10\) degree grid are investigated to derive a global and generally valid picture about the best length and orientation of Intensive baselines. Our results reveal that especially equatorial baselines or baselines with a center close to the equatorial plane are not suited for Intensives although they provide a good east–west extension. This is explained by the narrow right ascension band of visible sources and the resulting lack of variety in the partial derivatives. Moreover, it is shown that north–south baselines are also capable of determining dUT1 with reasonable accuracy, given that the baseline orientation is significantly different from the Earth rotation axis. However, great care must be taken to provide accurate polar motion a priori information for these baselines. Finally, we provide a better metric to assess the suitability of Intensive baselines based on the effective spread of \(\partial \tau /\partial dUT1\).

甚长基线干涉测量 (VLBI) 的主要任务之一是快速确定通过世界时 UT1 和协调世界时 UTC (dUT1) 之间的差异表示的高度可变的地球自转。出于这个原因，每天都会观察专门的一小时、单一的基线会议，称为“强化”。到目前为止，Intensive的最优几何会议被认为包括基线的东西向延伸，以确保以最高精度进行 dUT1 估计。在本出版物中，我们证明了长东西向基线仅是特定长度和方向的最佳选择。在这方面，最佳取向甚至可能需要基线相对于赤道平面有很大的倾斜。这些发现的基础是模拟研究，随后对观察到的群延迟\(\tau \)相对于 dUT1 \(\partial \tau /\partial dUT1\)的偏导数进行了研究。位于常规\(10 \times 10\)上的人工站之间的近 3000 条基线度网格被调查以获得关于强化基线的最佳长度和方向的全局和普遍有效的图片。我们的结果表明，特别是赤道基线或中心靠近赤道平面的基线不适合密集型尽管它们提供了良好的东西向延伸。这是由可见光源的狭窄赤经带和由此导致的偏导数缺乏多样性来解释的。此外，研究表明，考虑到基线方向与地球自转轴显着不同，南北基线也能够以合理的精度确定 dUT1。然而，必须非常小心地为这些基线提供准确的极移先验信息。最后，我们提供了一个更好的指标来评估基于\(\partial \tau /\partial dUT1\)的有效传播的强化基线的适用性。