基于改进短时傅里叶变换的磁共振随机噪声消减方法  

Random noise suppression of magnetic resonance sounding signal based on modified short-time Fourier transform

作　　者：林婷婷[1,2] 李玥 高兴 万玲[1,2] Lin Ting-Ting;Li Yue;Gao Xing;Wan Ling(College of Instrumentation&Electrical Engineering,Jilin University,Changchun 130026,China;Key Laboratory of Geophysical Exploration Equipment,Ministry of Education,Jilin University,Changchun 130026,China)

机构地区：[1]吉林大学仪器科学与电气工程学院,长春130026 [2]吉林大学,地球信息探测仪器教育部重点实验室,长春130026

出　　处：《物理学报》2021年第16期128-140,共13页Acta Physica Sinica

基　　金：国家自然科学基金优秀青年科学基金(批准号:41722405);国家自然科学基金(批准号:41874209,41974208);吉林省科技厅重点科技研发项目(批准号:20180201017GX);吉林省科技发展计划(批准号:20180520183JH);吉林大学博士研究生交叉学科科研资助计划(批准号:101832020DJX066)资助的课题。

摘　　要：磁共振测深法(magnetic resonance sounding,MRS)具有无需钻探即可直接探测地下水含量的优势,但是极低的信噪比(signal-to-noise ratio,SNR)限制了该方法的大范围应用,目前的研究工作主要集中在消除MRS信号中的尖峰噪声和工频谐波噪声上,而随机噪声由于其无规律性导致难以消除,但是它的影响不容忽视.目前MRS随机噪声的消减常采用叠加法,需要重复采集数据叠加平均来达到消噪目的,探测时间长且消噪效果有限.针对这一问题,本文提出了一种改进的短时傅里叶变换方法,该方法通过处理单次采集的MRS包络信号来降低数据量,提高数据处理效率.改进的短时傅里叶变换方法采用解析信号代替常规短时傅里叶变换中的实值信号,提高MRS信号时频域瞬时幅度的准确度,得到MRS信号的高精度时频分布,然后提取时频域峰值幅度和峰值相位重构信号来消除随机噪声.仿真实验和实测数据处理结果表明,该方法能够直接处理单次采集数据,在信噪比高于-17.21 dB的情况下可有效提取MRS信号,实现随机噪声的压制,且与传统叠加法相比,信噪比最多可提高27.88 dB,均方根误差最多缩小36.44倍,参数估计值更加准确.本文的研究结果为利用MRS获取准确的地下水分布情况奠定了良好的基础.Magnetic resonance sounding(MRS)has the advantage of detecting groundwater content directly without drilling,but the signal-to-noise ratio(SNR)is extremely low which limits the application of the method.Most of the current researches focus on eliminating spikes and powerline harmonic noise in the MRS signal,whereas the influence of random noise cannot be ignored even though it is difficult to suppress due to the irregularity.The common method to eliminate MRS random noise is stacking which requires extensive measurement repetition at the cost of detection efficiency,and it is insufficient when employed in a high-level noise surrounding.To solve this problem,we propose a modified short-time Fourier transform(MSTFT)method,in which used is the short-time Fourier transform on the analytical signal instead of the real-valued signal to obtain the high-precision time-frequency distribution of MRS signal,followed by extracting the time-frequency domain peak amplitude and peak phase to reconstruct the signal and suppress the random noise.The performance of the proposed method is tested on synthetic envelope signals and field data.The using of the MSTFT method to handle a single recording can suppress the random noise and extract MRS signals when SNR is more than-17.21 dB.Compared with the stacking method,the MSTFT achieves an 27.88 dB increase of SNR and more accurate parameter estimation.The findings of this study lay a good foundation for obtaining exact groundwater distribution by utilizing magnetic resonance sounding.

关 键 词：地面磁共振技术 随机噪声 改进短时傅里叶变换 数据处理 

分 类 号：P641.7[天文地球—地质矿产勘探]