Interferometric Seismometer Research and Development

我们研制一种新型地震计已有几年了。我们使用一种依靠光学干涉测量的新技术来代替传统的电子式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，这项技术具有显著的优势。最重要的是：简单稳定的校准，远低于地震频率的良好性能(例如，潮汐观测)，在非常高的温度下工作的可能性，以及在不需要井下电子的情况下在井下工作的能力。新型地震仪使用光纤将激光传输到装有钟摆(对于水平传感器)或悬挂在弹簧上的质量(对于垂直传感器)的探头。一个偏振敏感的迈克尔逊干涉仪，两个反射器中的一个安装在钟摆(或弹簧安装的质量)上，跟踪位移。两根光纤将正交条纹信号传送到光电探测器和信号处理器，信号处理器将光信号转换为质量位移。这一信号将被进一步分析以产生地面加速度。在我们预计将是传感器开发的最后阶段，我们计划建造一个新的垂直悬架，增加动态范围，改进光学信号分析，增加激光波长控制，并研究热补偿。此外，我们还将研究噪声源，并建立非线性和交叉耦合的校正。(2)非技术描述地震计是一种非常简单的装置？它是弹簧上的一个质量块。地面震动是通过记录质量相对于外壳的位置来检测的。然而，有趣的地面震动的程度在一个巨大的范围内变化，从附近的地震，可能导致许多厘米的幅度的震动，到由整个地球的振铃引起的微小运动(小于原子直径)。全球地震台网(GSN)由全球100多个台站组成，用于记录这些微小的地震信号。对它们的分析是我们研究地球最有效的手段？S。大多数地震仪都是用电子器件来记录质量运动的。虽然这总体上是成功的，但电子产品也有一些局限性，电子系统在偏远和崎岖的环境中持续运行带来了许多困难。我们发明了一种用激光和光纤测量微小质量运动的替代方法。本文提出的研究将进一步推动这一新技术向实用、易懂、全特性、可靠、井下和拱顶可展开的宽带地震仪的方向发展。在保持GSN的性能目标的同时，将强调将尺寸、功率需求和成本降至最低。

(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.