1. China Geological Equipment Research Institute Co., Ltd., Beijing 100011, China 2. China Geological Equipment Group Co., Ltd., Beijing 100102, China 3. Key Laboratory of Shale Gas and Geoengineering, CAS, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China 4. Institutions of Earth Science, Chinese Academy of Sciences, Beijing 100029, China 5. University of Chinese Academy of Sciences, Beijing 100049, China
Multi-channel transient electromagnetic data suffer seriously from cultural noise, and removal of periodic cultural disturbance has been a major problem in the multi-channel transient electromagnetic method. In some cases with only quite a few power lines configured regularly, the power line interference can be reduced by exchanging the receiver and source. The method by reversing source current polarity then stacking them period-by-period works better for step-current source. When only homogeneous earth is considered, the perpendicular electric component, which is in fact noise, can be measured and then subtracted from the in-line electric component. Digital recursive notching is a relatively robust way in which the periodic noise can be suppressed. It is well known that recursive notching is very fast; however, holes resulting from pre-deconvolution notching and transient response of digital recursive notcher has to be highly regarded. In this paper, several key points in removal of periodic power line noise in multi-channel transient electromagnetic data using digital recursive notch are studied. First of all, a modified version of so-called zero-pole digital recursive notcher design method, where filter coefficients are evaluated from notch width that makes significant physical sense and make analysis more clear, is proposed. After that, research on post-deconvolution notching, which directly deals with earth impulse response, is conducted. In addition, factors influencing transient response and notch result, such as notch width, initial conditions, and shape of earth impulse response, are analyzed. The results indicate that appropriate selection of initial conditions can effectively reduce the transient response of digital recursive notcher and thus remove periodic noise in earth impulse. Finally, reasonable result is obtained by applying the post-deconvolution digital recursive notch to real field data.
Di Q Y, Lei D, Wang Z X , et al. An integrated test of the multi-channel transient electromagnetic system[J]. Chinese Journal of Geophysics, 2016,9(12):4399-4407.
Ziolkowski A . Developments in the transient electromagnetic method[J]. First break, 2007,25:99-106.
Ziolkowski A, Wright D, Hall G, et al. Successful transient EM survey in the North Sea at 100 m water depth [C]// SEG Technical Program Expanded Abstracts 2008. Society of Exploration Geophysicists, 2008: 667-671
Ziolkowski A, Parr R, Wright D , et al. Multi-transient electromagnetic repeatability experiment over the North Sea Harding field[J]. Geophyiscal Prospecting, 2010,58:1159-1176.
Olalekan F, Di Q, Wang R, et al. Enhancement of subsurface resistivity distribution mapping using MTEM dense reverse source array: A case study of Anambra basin, Nigeria [C]// 7th International Conference on Environmental and Engineering Geophysics & Summit Forum of Chinese Academy of Engineering on Engineering Science and Technology, 2016: 8-10.
Olalekan Fayemi, Qingyun Di . Qualitative analysis of MTEM response using instantaneous attributes[J]. Journal of Applied Geophysics, 2017,46:37-45.
Zhang W W, Zhen Q H, Di Q Y . Study on MTEM frequency-domain ratio method and apparent resistivity calculation Chinese[J]. Journal of Geophysics, 2018,61(10):4171-4181.
Wright D A, Ziolkowski A. Suppression of Noise in MTEM data [C]// SEG Technical Program Expanded Abstracts, 2007: 549-553.
Spies B R . Local noise prediction filtering for central induction transient electromagnetic sounding[J]. Geophysics, 1988,8:1068-1079.
Wright D A . Detection of hydrocarbons and their movement in a reservoir using time-lapse multichannel transient electromagnetic (MTEM) data[D]. Edinburgh: The University of Edinburgh, 2004.
Strack K M, Hanstein T H, Eilenz H N . LOTEM data processing for areas with high cultural noise levels[J]. Physics of the Earth and Planetary Interiors, 1989,53:261-269.
Strack K M . Exploration with deep transient electromagnetics[M]. Elsevier, Amsterdam-London-New York-Tokyo, 1992: 52-55.
张文伟 . 多通道瞬变电磁数据处理研究[D].北京:中国科学院大学. 2018.
Zhang W W . Research on data processing of Multi-channel transient electromagnetic method[D]. Beijing: The University of Chinese Academy of Sciences, 2018.
Pei Soo-Chang, Tseng Chien-Cheng . Elimination of AC interference in electrocardiogram using IIR notch filter with transient suppression[J]. IEEE Transactions on Biomedical Engineering, 1995,42(11):1128-1132.
Carney R . Design of a digital notch filter with tracking requirements[J]. IEEE transactions on Space Electronics and Telemery, 1963, SET-9(4):109-114.
Hirano K, Nishimura S, Mitra S K . Design of digital notch filters[J]. IEEE Transactions on Communications COM-22, 1974: 964-970.
Pei Soo-Chang, Tseng Chien-Cheng . IIR multiple notch filter design based on allpass filter[J]. IEEE TENCON — Digital Signal Processing Applications, 1996: 267-271.
Piskorowski J . Digital Q-varying notch IIR filter with transient suppression[J]. IEEE Transactions on Instrumentation and Measurement, 2010,59(4):866-872.
Piskorowski J . Suppressing harmonic powerline interference using multiple-notch filtering methods with improved transient behavior[J]. Measurement, 2012,45:1350-1361.
Smith S W. The scientist and engineer’s guide to aigital signal processing[M]. California Technical Publishing, San Diego, 1997: 328-332.
Ziolkowski A . Wiener estimation of the Green’s function[J]. Geophysics, 2013,78(5):W31-W44.