摘要
长偏移距瞬变电磁法用于地下深部勘探时,观测到的垂直磁场脉冲响应非常微弱,常伴有严重噪声,从原始信号中消除噪声获得有用信息非常重要。为此笔者研究小波阈值方案对长瞬变电磁信号的去噪能力。实验中对西部某勘探区垂直磁场信号采用Sqtwolog,SURE,Heuristic和Minimax等阈值方案进行小波去噪比较,结果表明:几种小波阈值去噪方案对瞬变电磁法垂直磁场的染噪信号均能提高一定量的信噪比,达到较好的去噪效果;不同的阈值方案去噪效果各有差异,采用启发式阈值方案对实验数据处理效果要优于其它几种方案,因此根据信号统计分布特征选择合适方案去噪效果;实测信号去噪结果包含信息需要结合勘探区情况分析,是地下电性特征的反映还是未去除的噪声要慎重对待。在长偏移距电性源瞬变电磁法用于地下深部勘探时,利用适当小波阈值去噪处理可以对资料处理工作带来有益的帮助。
The long-offset transient electromagnetic （LOTEM） method measures induced electromotive force from source variation in loop receiver at distance using finite long grounded wire. The vertical magnetic-field impulse response on the surface of the earth is weak in deep exploration, which constantly submerged in noise and background signal. The aim of our study is to compare several wavelet denoising threshold rules on the transient electromagnetic response. Four kinds of wavelet threshold, Stein＇s unbiased estimate of risk, minimax threshold, heuristic threshold and fixed threshold are introduced and experimented in the practical transient electromagnetic data. Results indicated that the heuristic threshold excels among them on the electric field and magnetic field responses respectively. The results show that it will be helpful to make full use of the wavelet threshold rules for the data processing and explanation of TEM exploration.
出处
《工程地球物理学报》
2008年第1期70-74,共5页
Chinese Journal of Engineering Geophysics
关键词
长偏移距瞬变电磁
多分辨分析
小波变换
去噪
transient electromagnetic （TEM）
multiresolution analysis
wavelet
denoising
