【作者】 李晓鹏；

【导师】 席继楼；

【作者基本信息】 中国地震局地震预测研究所 ， 固体地球物理， 2011， 硕士

【摘要】 地电阻率观测对于探测地球内部的电性结构、地震前兆监测研究具有很重要的现实意义。在地电观测场地干扰日益严重的今天,我国地电观测台站面临着各种各样的干扰。因此,抗干扰观测方法已经成为地电观测台站中不可或缺的技术环节。本论文根据地电阻率的观测特点,结合国内外已有的交流地电阻率观测技术发展动态,基于现有地电台站观测装置基础,研究了低频交流地电阻率观测中单一频率信号的提取,并探索其在抗干扰方面的技术可行性,为低频交流地电阻率观测方法的开展做一些前期研究。论文首先介绍了目前台站常见的干扰问题及一些抗干扰的手段,低频交流地电阻率法的理论基础,采用选频发射和同步选频接收的方式,达到避开干扰的目的。研究表明,在低频率信号在某些频段范围,交流场可以看作似稳场来处理,可采用与直流地电阻率观测方法相类似的四极法实现方式。分析了强噪声背景下信号的提取方法,分别讨论了FFT、自适应滤波、小波分析和多重自相关信号提取方法的原理。通过数值模拟对比,得到了小波分析方法和多重自相关的方法在较低噪声下有较好的处理结果。在进一步加大信号噪声时,小波分析的方法受到了限制,而多重自相关法仍然可以得到很好的处理结果。由于小波分析可以在大噪声背景下对信号进行预处理,因此,提出了一种新的方法,基于小波变换的多重自相关检测法,该方法对普通的小波变换做了改进,提出了Donoho阈值小波处理,在提高信噪比的基础上,作多重自相关检测,得到了更好的处理结果。论文最后对野外观测试验数据进行了分析,该试验旨在通过高采样数据采集系统对单一频率的低频信号进行提取和对加入干扰的低频信号进行提取,对其抗干扰性进行分析,达到了预期目标,并对其主要应用前景和当前存在的问题进行了讨论。本论文所讨论的分析和处理方法可以应用于其它的微弱电磁信号提取的分析和处理研究中。更多还原

【Abstract】 Geo-resistivity observation has important practical significance in detecting the electrical structure of the earth’s interior and monitoring the earthquake precursor. Nowadays, our stations for geo-electrical are facing with a variety of interference. Therefore, anti-interference method has become an essential technology for the geo-electrical observation stations. According to the characteristics of the geo-electrical resistivity, this paper studied the low-frequency AC geo-resistivity observed in single-frequency signal extraction which has carried out some preliminary research for developing low-frequency AC geo-resistivity methods. The creative research jobs and results are as follows:Firstly, the current common interference and some anti-interference measures are introduced to bring forward the theory of low-frequency AC geo-resistivity methods. Investments showed that interference could be avoided by frequency-selection transmitting and synchronization receiving and that in some frequency range of low-frequency signal, alternating current field seemed to be Quasi-Stationary Field which could employ a Four-Pole method that had been used in DC geo- resistivity.Secondly, principles of FFT, adaptive filtering, wavelet analysis and multi-layer auto-correlation are discussed respectively to extract signals from strong-noising background. Comparison research on the numerical simulation showed that it is effective to get better results in a weak-noising background by means of wavelet analysis and multi-layer auto-correlation. When the noise began to accumulate, however, the wavelet analysis method would be of little use while the multi-layer auto-correlation could still get comparatively more ideal results. Considering wavelet analysis could do some pre-processing jobs to distinguish signal from strong-noising background, we propounded a method of Multi-layer auto-correlation detection based on wavelet transform and a de-noising method of Donoho threshold wavelet process to get preferable results and a higher S/N(signal to noise ratio) through multi-layer auto-correlation detecting.Finally, the anti-interference properties of field observation test data are analyzed, which aimed at extracting low-frequency signal of single frequency by high-sampling data acquisition system, to achieve its intended goals. And then its main application prospects and current problems are discussed in the end. Test result shows that it is helpful to apply the methods this paper developed in other weak electro-magnetic signal extraction analysis.更多还原