Recalibration of OBSIP Instrument Orientations

海底地震仪（OBSs）位于海底，记录地震。它们是从一艘研究船上部署的。仪器被释放到海洋表面，OBS下沉并降落在海底。它如何着陆以及仪器如何与地理坐标系对齐是未知的。地震仪周围的万向节系统确保它是直立的，但不检查仪器所面对的方向。陆地上的地震仪可以用指南针来定位，但目前在海底还不可能。然而，地震数据的分析依赖于知道仪器的方向。为了解决这个问题，将开发一种标准化的自动化工具，以提供OBS仪器方向的最佳估计。该工具基于对全球浅层地震的地震表面波的到达角测量。在开发出新的自动化工具后，将通过将结果与旧的高精度测量结果进行比较来验证，但是手工和耗时的测量已经完成。最终的代码将被公开发布，并成为一个社区工具。许多地震数据分析，如接收函数、剪切波分裂和洛夫波频散，都依赖于完整的三分量地震记录的处理。对于这些分析，了解相对于地理坐标系的水平分量的对齐是先决条件。在陆地上，这些信息很容易通过指南针的交叉核对得到。在海洋中，自由落体海底地震仪（OBSs）以未知的方向下沉。仪器的声学测量成本过高，地震仪组件方向的确定通常留给个人数据最终用户。重新定位与预期的数据分析同时进行，通常没有详细评估复杂介质中不均匀事件覆盖和波传播的偏差。该项目将开发一个标准化的自动化工具，为OBS仪器定向提供最佳估计。考虑到海洋环境的限制和噪音水平，长周期瑞利波可能仍然是确定仪器方向的最佳工具。新工具箱将与旧的、完善的交互式屏幕工具进行仔细的对比。后者已被证明不适合其他人使用，因为它包含旧的、不兼容的遗留代码。新工具将由Python和Fortran代码的组合组成，并将提供对IRIS数据管理中心数据的自动访问。

Ocean bottom seismometers (OBSs) sit on the seafloor and record earthquakes. They are deployed from a research vessel. The instrument is released on the ocean surface, the OBS sinks and lands on the seafloor. How it lands and how the instruments are aligned with the geographic coordinate system is unknown. A gimbal system surrounding the seismometer makes sure that it is upright, but no check is made on which direction the instrument is facing. Seismometers on land can be oriented using a compass, but this is not currently possible on the seafloor. The analysis of seismic data, however, is dependent on knowing the orientation of the instrument. To address this problem, a standardized, automated tool will be developed to provide the best possible estimates for OBS instrument orientations. The tool is based on arrival angle measurements on seismic surface waves from shallow earthquakes around the globe. After development of the new automated tool it will be validated by comparing results to older high-precision, but hands-on and time consuming measurements that have been made. The resulting code will be released publically and become a community tool.Many seismic data analyses, such as receiver functions, shear-wave splitting and Love wave dispersion, rely on the processing of a complete 3-component seismogram. For these analyses, knowledge of the alignment of the horizontal components with respect to the geographic coordinate system is a prerequisite. On land, this information is easy and routinely obtained through cross-check with a compass. In the oceans, free-fall ocean bottom seismometers (OBSs) sink with unknown orientation. Acoustic surveys of the instrument are cost-prohibitive, and the determination of the orientation of seismometer components is usually left to the individual data end user. Reorientation is done concurrently with the intended data analysis, often without detailed assessment of biases from uneven event coverage and wave propagation in complex media. This project will develop a standardized automated tool to provide optimal estimates for OBS instrument orientations. Long-period Rayleigh waves likely remain the best tool to determine instrument orientations given the restrictions and noise levels of an ocean environment. The new toolbox will be carefully bench marked against an older, well-established interactive-screen tool. The latter has proven impractical to be used by others because it contains old, non-compliant legacy code. The new tool will consist of a combination of Python and Fortran codes and will provide automated access to data at the IRIS Data Management Center.