Interferometric Seismometer Research and Development

技术说明几年来我们一直在研制一种新型地震仪。我们使用一种新技术，依靠光学干涉测量取代传统的电子位移传感器来测量惯性质量的运动。与目前广泛使用的传统电子反馈地震仪相比，该技术具有显著的优势。最重要的是：简单稳定的校准，良好的性能远低于地震频率（例如潮汐观测），在非常高的温度下工作的可能性，以及无需井下电子设备即可在井眼中工作的能力。新的地震仪使用光纤将激光传送到一个装有钟摆（用于水平传感器）或悬挂在弹簧上的质量（用于垂直传感器）的探空仪。偏振敏感的迈克尔逊干涉仪与安装在摆（或弹簧安装质量）上的两个反射器之一跟踪位移。两根光纤将条纹信号以正交的方式传送到光电探测器和将光信号转换为质量位移的信号处理器。对该信号进行进一步分析，得出地面加速度。在我们期望的传感器开发的最后阶段，我们计划建立一个新的垂直悬架，增加动态范围，改进光信号分析，增加激光波长控制，并研究热补偿。此外，我们将研究噪声源并建立非线性和交叉耦合的校正。(2)非技术说明地震仪是一种非常简单的装置。它是弹簧上的质量。地面震动是通过记录物体相对于其外壳的位置来检测的。然而，令人感兴趣的地面震动的程度在很大的范围内变化，从附近的地震，可以引起振幅达几厘米的震动，到整个地球的震动引起的微小运动（小于原子直径）。全球地震台网（GSN）由全球100多个台站组成，记录这些微小的地震信号。分析它们是我们研究地球最有效的手段吗？室内。大多数地震仪使用电子设备来记录质量运动。虽然这种方法总体上是成功的，但电子设备有一些局限性，并且电子系统在远程和恶劣环境中连续运行存在许多困难。我们发明了另一种方法，使用激光和光纤来测量微小的质量运动。本文提出的研究将进一步推进这项新技术，使其成为一套实用的、易于理解的、特性充分的、可靠的、可在钻孔和vault部署的宽带地震仪。在保持GSN的性能目标的同时，将强调尺寸、功率需求和成本的最小化。

(1) Technical descriptionWe have been developing a new type of seismometer for several years. We use a new technology that relies on optical interferometry in place of the traditional electronic displacement transducer to measure the motion of an inertial mass. This technology offers significant advantages over the conventional electronic-feedback seismometers in wide use today. The most important ones are: simple and stable calibration, good performance well below seismic frequencies (for tidal observations, for example), the possibility to operate at very high temperature, and the capability to operate in a borehole without the need for down hole electronics.The new seismometers use optical fibers to carry laser light to a sonde housing a pendulum (for horizontal sensors) or a mass suspended from a spring (for vertical sensors). A polarization sensitive Michelson interferometer with one of two reflectors mounted on the pendulum (or spring-mounted mass) tracks the displacement. Two optical fibers carry fringe signals in quadrature to photodetectors and a signal processor which transforms the optical signals to mass displacement. This signal is further analyzed to yield ground acceleration.In what we expect will be the final phase of the sensor development, we plan to build a new vertical suspension, increase the dynamic range, improve the optical signal analysis, add laser wavelength control, and investigate thermal compensation. In addition we will study noise sources and establish corrections for non-linearity and cross coupling.(2) Non-technical descriptionA seismometer is a very simple device ? it is a mass on a spring. Ground shaking is detected by recording the position of the mass relative to its housing. However the level of interesting ground shaking varies over an enormous range, from nearby earthquakes, which can cause shaking with an amplitude of many centimeters, to the minute motions (less than an atomic diameter) caused by the ringing of the entire Earth. A global seismic network (GSN) consists of over a 100 stations worldwide to record these tiny seismic signals. Analysis of them is the most effective means we have to study Earth?s interior.Most seismometers use electronics to record the mass motion. While this has been generally successful, electronics have some limitations and many difficulties come with electronic systems operating continuously in remote and rugged environments. We have invented an alternative means using laser light and optical fibers to measure the minute mass motions. The research proposed here will further advance this new technology into a practical, well understood, fully characterized, reliable, borehole and vault deployable set of broadband seismometers. Minimization of size, power requirement, and cost will be emphasized while maintaining the performance goals of the GSN.