Accurate orientation of geodetic instruments is fundamental for understanding deformation processes within the Earth's interior. Misalignment can lead to significant errors in data interpretation, affecting various geophysical applications. However, accurate alignment of standalone instruments like seismometers, strainmeters and tiltmeters remains a challenge in field geodesy. While numerous seismic-wave-based orientation methods have been successfully applied to seismometers, they are often inapplicable to tiltmeters due to their high-frequency filtering behavior and the requirement for a neighboring, pre-oriented instrument. In response to these challenges, we propose a novel orientation calibration method for borehole tiltmeters based on maximizing the correlation between recorded tilt data and theoretical tides by adjusting azimuthal angles. Our study encompasses two kinds of borehole tiltmeters and four datasets from three different field sites. Using solid and ocean tides modeling together with local topography and cavity disturbances, we obtain coefficient correlations ranging between 0.831 and 0.963, and 95% confidence intervals of azimuthal angles below 3.3°. The correlation-based method demonstrates robustness across various tidal-signal extraction techniques, including different averaging window sizes and band-pass filters. Moreover, it yields azimuthal results in agreement with direct compass measurements for known orientations, while exhibiting a moderate sensitivity to factors such as ocean tides and site-specific topography for the studied cases. This method appears to be advantageous when direct measurements are either unavailable or challenging, and emerges as an accurate tool for determining borehole tiltmeter orientation. Its potential applicability may extend beyond tiltmeters to other instruments that can also record tidal phenomena, such as strainmeters and broadband seismometers. Additionally, its utility could be extended to environments like the seafloor, in order to refine the precision of azimuthal angle estimation and simplify methods for azimuthal angle determination.

大地测量仪器的精确定向是了解地球内部变形过程的基础。未对准可能会导致数据解释出现重大错误，影响各种地球物理应用。然而，地震仪、应变仪和倾斜仪等独立仪器的精确对准仍然是野外大地测量中的一个挑战。虽然许多基于地震波的定向方法已成功应用于地震计，但由于倾斜计的高频滤波行为以及对邻近预定向仪器的要求，它们通常不适用于倾斜计。针对这些挑战，我们提出了一种新颖的钻孔倾斜计定向校准方法，该方法通过调整方位角来最大化记录的倾斜数据和理论潮汐之间的相关性。我们的研究包括两种钻孔倾斜仪和来自三个不同现场站点的四个数据集。使用固体和海洋潮汐建模以及局部地形和空腔扰动，我们获得了介于 0.831 和 0.963 之间的系数相关性，以及低于 3.3° 的方位角的 95% 置信区间。基于相关性的方法证明了各种潮汐信号提取技术的鲁棒性，包括不同的平均窗口大小和带通滤波器。此外，它产生的方位角结果与已知方向的直接罗盘测量一致，同时对所研究案例的海潮和特定地点地形等因素表现出中等敏感性。当直接测量不可用或具有挑战性时，该方法似乎是有利的，并且成为确定钻孔倾斜计方向的准确工具。 它的潜在适用性可能会超出倾斜计，扩展到其他也可以记录潮汐现象的仪器，例如应变计和宽带地震计。此外，它的实用性可以扩展到海底等环境，以提高方位角估计的精度并简化方位角确定的方法。