【作者】 王宁；

【导师】 牛建军；

【作者基本信息】 吉林大学 ， 地质工程， 2023， 硕士

【摘要】 音频大地电磁测深法是一种重要的地球物理勘探方法,它以天然的大地电磁场为场源,利用观测到的电场分量与磁场分量估计出阻抗,进而计算出地下岩土层电性结构,从而实现勘探目的。该方法因为不受高阻屏蔽、仪器轻便等优点,被广泛应用于工程勘查中。但音频大地电磁测深法的观测频带范围内,极易受到各种噪声的干扰,若不加以处理,将导致最终的反演结果与真实值产生很大偏差。因此,如何将数据中的噪声进行有效的压制,以提高音频大地电磁测深法的数据质量,是一个值得研究的问题。本文以提高音频大地电磁测深数据质量为出发点,在时间域中对采集数据进行去噪的研究。在充分了解音频大地电磁测深法原理的基础上,对天然的大地电磁场场源特征进行了研究,并对实测数据中的常见人文噪声干扰在时间序列的特征及产生的影响进行了系统分析。针对音频大地电磁测深数据易受噪声干扰的情况,引入了小波分析的方法,在时间域中选用不同参数对噪声进行处理,通过对比分析去噪结果,选取出了针对脉冲噪声及方波噪声的最优组合参数。由数值模拟结果可知,小波去噪对于高斯白噪声有着很好的压制效果,但对于脉冲及方波噪声压制效果不理想。针对这一情况,本文提出了小波阈值去噪与变分模态分解相结合的方法,将其应用于含噪数据中进行去噪,结果表明,该方法可以有效地压制脉冲噪声和方波噪声。为了进一步验证该方法的有效性,将其应用于实测数据的处理中,通过对比分析去噪前后阻抗曲线的变化,证明了该方法能够有效压制噪声。最终将研究成果应用于大沟河输水隧洞勘探项目中,极大地改善了数据质量。更多还原

【Abstract】 Audio magnetotelluric sounding uses the natural geomagnetic field as the field source,estimates the impedance using the observed electric field and magnetic field components,and then calculates the electrical structure of the underground rock and soil layer,so as to achieve the exploration purpose.This method is widely used in engineering exploration because it is not shielded by high resistance and the instrument is lightweight.However,the audio magnetotelluric sounding method is very susceptible to noise interference within the observation frequency band.If not processed,the interpretation results will be affected.Therefore,how to suppress noise in time-domain data effectively to improve the data quality of audio-magnetotelluric sounding is a problem worth studying.This paper takes improving the accuracy of audio magnetotelluric sounding as a starting point,and studies the noise removal of the collected data in time domain.On the basis of fully understanding the audio-magnetotelluric sounding method,the characteristics of natural magnetotelluric field sources are studied,the waveforms of common human noise disturbances in the measured data in time series and their possible effects are systematically analyzed.In view of the noise interference of audio magnetotelluric sounding data,the means of wavelet analysis is introduced,and the threshold denoising method of wavelet analysis is selected as the data processing method.The effect of different parameters of the method on noise suppression is analyzed in detail,and the signal-to-noise ratio and root mean square error are used as the objective evaluation index of the denoising effect.By processing the analog signal,the optimal combination parameters for pulse and square noise are selected.Through analysis,it is found that the wavelet threshold denoising method has a good suppressing effect on white Gaussian noise,but not on pulse and square noise.In this case,a combination of wavelet threshold denoising and variational mode decomposition is presented.The results of numerical simulation show that this method can suppress impulse and square noise very well.In order to further verify the validity of this method,it is applied to the processing and analysis of the measured data.By comparing the impedance curves before and after noise removal,it shows that this method can suppress noise.In order to validate the effectiveness of this method,the research results are applied to the exploration project of Dagou River water transmission tunnel,which greatly improves the exploration accuracy.更多还原