【作者】 周忠海；

【导师】 翟世奎；

【作者基本信息】 中国海洋大学 ， 海洋地质， 2009， 博士

【摘要】 二十一世纪是海洋的世纪,海洋经济在很多国家的经济中所占的比重越来越大。然而,我国的海洋灾害频发,造成巨大的生命财产损失。做好海洋灾害预警工作可以有效地促进国家的经济发展和保障人民的生命财产安全。本文依托于国家科技部国际科技合作计划项目“基于激光干涉原理的海洋灾害预警系统”(课题编号:2008DFR20230)。首先总结了我国海洋动力灾害的现状和世界各国使用的地球动力学检测技术;然后介绍了项目中所使用激光干涉测量装置,及其所获得的干涉图像的处理办法;最后以俄方建成的两个相距250公里的实验站为依托,完成了关于地球动力和地壳微形变之间关系的实验研究,并对实验数据进行了分析,得出了相关的结论。本文创新性的提出了采用激光干涉技术来测量海洋动力灾害所引起的地壳的微小形变。采用的激光干涉测量装置的位移测量精度可达到10-11m,能够检测频率从0Hz开始的地壳振动,具有良好的低频响应特性,对地壳常见的低频振动具有良好的响应,这些特性是其它地球动力学检测方法所不具备的。本文的主要工作如下:1、检测装置的测量精度和稳定度完全取决于激光源的频率稳定性及其相干性,因此,选择频率非常稳定He-Ne激光器作为测量装置的光源,能够保证光束在长光程上同样具有非常好的相干特性。在光信号传输过程中采用增压光束导管,将光信号受传播噪声的影响降到最小。2、在干涉仪的设计上,为了增加系统的灵敏度,采用了臂长为52.5m的迈克尔逊激光干涉仪。干涉仪的动镜是激光干涉仪中唯一不断运动的部件,其在运动过程中的平稳性保证干涉图像和复原光谱的质量。采用准猫眼动镜有效克服了动镜倾斜带来的对光谱质量的影响,并在文中分析了准猫眼动镜的工作原理,同时给出了准猫眼动镜的选择原则。激光干涉仪参考臂由具有调制和补偿功能的双PZT组构成,分析了双PZT组的最佳组合方式,及其在调制信号和反馈补偿信号作用下对干涉测量仪光程差的改变情况。上述这些方法最终解决了激光干涉仪测量低频微小振动中的关键技术问题。3、我们通过使用间隔布置的激光干涉仪进行测量,发现了海洋内波和表面波可以造成地壳水平方向上的微应变。同时,我们从实验角度揭示了采用激光干涉仪测量地震先兆的可能性。4、研究了水声波到声震波的转换。当水声源在岩基或斜坡后面时,地震波信号就会被不同的低频信号调制。在深海或浅海里安置低频水声源,通过激光干涉仪接收到的水声振荡波信号的变化,发现了水声波以接近临界角的方式作用在海底,并且最终转变为地震声波。5、证实了海洋内波能量不转换为小规模湍流能量,而是转换为海底(岩石圈)弹性振动能量。海洋表面波和内波与海底交互作用过程中,能量大多以Rayleigh波的形式被岩石圈吸收。6、本文分析了日本海大陆架区域由海洋内在重力波导致的低频岩石圈变形的数据,得出当波浪由大陆架边缘向日本海海岸传播时,周期可能会随着压力的增加而增大,并且伴随着地球重力波幅值增加的结论。以上研究成果表明激光干涉测量技术可以为海洋动力灾害预警提供科学的检测数据。更多还原

【Abstract】 The 21st century is a century for sea and ocean. The sea economy takes more and more proportions of national economy in many countries. However, marine calamity happens frequently in China and causes giant loss of life and property. The marine calamity forecast can effectively promote economy development and safeguard life and property safety.This article depends on a research project from the International Science and Technology Corporation Plan organized by the Ministry of Science and Technology of the People′s Republic of China: Marine Calamity Forecast System Based On Laser Interferometry (project serial number: 2008DFR20230). Firstly, the current situation of China’s sea power disaster and the measuring technology for geodynamics in different countries are summarized; then the laser interferometer adopted in this project and the processing techniques for interference pattern are introduced; Finally, the relation between the Earth power and the micro deformation of Earth’s crust is experimentally studied at two 250-kilometer-seperated experimental stations constructed in Russia; the empirical data are scientifically analyzed, and related conclusions are drawn.Using the laser interference technology to measure the infinitesimal deformation of the Earth’s crust is innovatively proposed. Common vibration with low-frequency of the Earth’s crust can be measured with a displacement measuring accuracy around 10-11m. This good response to low-frequency vibration is a unique characteristic of laser interference technology.The prime tasks of this article are as follows:1、The measuring accuracy and the stability are completely decided by the frequency stability and the coherence of the laser source. Therefore, choosing He-Ne laser with extremely stable frequency as light source can guarantee an extremely good coherent characteristic in a long optical path. 2、In order to increase the sensitivity, a Michaelson laser interferometer with a 52.5-meter-long arm is adopted. The moving mirror is the only unceasing moving part in the laser interferometer. So the stability of moving mirror guarantees the quality of interference pattern and the spectrum restoration. A cat-eye moving mirror is used to overcome the influence from the tilt of moving mirror. The working principle and the selecting principle of cat-eye moving mirror are also analyzed simultaneously. The reference arm of laser interferometer was constituted of PZT groups with modulation and compensation function. The optimal combination of PZT groups and the optical path changes induced by modulation signal and feedback compensation signal are also analyzed. The above methods solve the key technological problem in measuring low-frequency small vibration by laser interferometer.3、From the measurements of spaced laser strainmeters, the horizontal crustal microstrains caused by surface and internal sea waves are observed. The possibility of earthquake forecast is experimentally revealed.4、The conversion from low-frequency hydroacoustic source to seismoacoustic signals is studied. When a hydroacoustic source is located on shelf or behind slope, seismoacoustic signals are modulated by various low-frequency signals. By using a low-frequency hydroacoustic source in a shallow or deep sea to generate hydroacoustic oscillations, the variations of signals received by a laser deformograph reveal that the hydroacoustic wave interacts with the bottom at around critical angles and transforms into a seismoacoustic wave.5、We testified that the energy of internal sea waves is transformed into the energy of elastic vibrations of the seafloor, instead of the energy of small-scale turbulence. During the interaction of internal and surface sea waves with the seafloor, the energy is mostly absorbed by the lithosphere in the form of Rayleigh waves.6、The data of low-frequency lithospheric deformations produced by marine internal gravitational waves (IGW) propagating in the continental shelf zone of the Sea of Japan are analyzed. A conclusion is deduced that wave period may increase as a result of additional pressure associated with an increase in the IGW amplitude during the waves propagate from the shelf edge toward the coast of the Sea of Japan. The above-mentioned research results indicated the laser interferometry technology may provide scientific data for marine calamity forecast.更多还原