强电磁干扰下磁共振地下水探测噪声压制方法研究进展

磁共振地下水探测方法因具有高分辨力、高效率、信息量丰富和解唯一等优点而备受地球物理工作者关注。近几年，该方法在正演模型和反演解释方面取得了显著的进展，在水文地质勘查方面的应用也进一步拓展。然而，磁共振信号极其微弱、对周围环境中的电磁干扰反映敏感，成为其应用的主要瓶颈。吉林大学地下水磁共振技术课题组针对噪声的产生机理及特性，对影响信号质量最严重的两类噪声--工频谐波噪声和尖峰脉冲噪声进行研究。本文综述了强电磁干扰下磁共振地下水探测噪声压制方法的研究现状及近期研究进展，包括磁共振信号的工频谐波噪声压制方法和尖峰脉冲噪声压制方法，简要介绍了实时参考消噪技术、独立分量分析技术、基于能量运算的尖峰噪声抑制技术以及基于同步压缩小波变换和自寻优非线性阈值补偿技术抑制电磁干扰的研究示例，展望了地下水磁共振探测噪声压制技术的未来发展趋势。

Progress of Magnetic Resonance Sounding for Groundwater Investigation Under High-Level Electromagnetic Interference

Magnetic resonance sounding (MRS) for groundwater investigation has received much attention of geophysicists due to its higher resolution, more efficiency, more information and unique interpretation for hydrogeological investigations. It has shown continuous development towards a frequently used geophysical technique over the last decades. There has been significant improvements in forward modeling, inversion and interpretation during the last years. These improvements extended the application range of the method concerning solutions to hydrogeological tasks. But the applicability of MRS is highly limited due to bad signal-to-noise (S/N) ratio. In many cases, the expected MRS signals are only few tens of nanovolts and therefore often contaminated by significant high-level electromagnetic noise. MRS group of Jilin University has studied the noise and its characteristics, and found that Power-line harmonic noise and spike noise are the most disturbing noises. The purpose of this paper is to give an overview of noise cancelling in MRS signal processing. We report the recent researches, including noise cancelling in real time, independent component analysis, spikes removal of MRS data based on energy calculation, as well as synchronous compression wavelet transform and self-optimizing nonlinear threshold compensation. By introducing several case studies, we prospect the developing trends of MRS noise cancelling.