基于数字递归陷波的多通道瞬变电磁法周期噪声去除研究

doi:10.11720/wtyht.2020.1428

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Abstract

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.

Key words： MTEM earth impulse response digital recursive notch transient response initial conditions

Received: 01 September 2019 Published: 22 April 2020

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Corresponding Authors: Qing-Yun DI E-mail: qydi@mail.iggcas.ac.cn

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	Wen-Wei ZHANG
	Qing-Yun DI
	Qi-Li GENG
	Da LEI
	Zhong-Xin WANG
	Jia-Jia MIAO

Cite this article:

Wen-Wei ZHANG,Qing-Yun DI,Qi-Li GENG, et al. The removal of MTEM periodic noise based on digital recursive notching[J]. Geophysical and Geochemical Exploration, 2020, 44(2): 278-289.

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https://www.wutanyuhuatan.com/EN/10.11720/wtyht.2020.1428 OR https://www.wutanyuhuatan.com/EN/Y2020/V44/I2/278

Sketch of notcher

Geometric interpretation of 2nd-order digital recursive notcher

Coefficients of 2nd-order digital recursive notcher

Spectrum of digital recursive notcher

Initial conditions of 2nd-order digital recursive notcher

Transient response of digital recursive notcher
a—first kind of initial condition;b—second kind of initial condition; c—third kind of initial condition

Earth impulse response of 25 Ω·m homogenous half space at an offset of 1 000 m and contaminated signal by 50 Hz sinusoidal noise

Influence of transient response on removal of periodical noise in earth impulse response
a—first kind of initial condition;b—second kind of initial condition; c—third kind of initial condition

Removal of periodic noise in impulse response of inhomogeneous earth
a—impulse response with air wave and contaminated signal by 50 Hz sinusoidal noise; b—impulse response without air wave and contaminated signal by 50 Hz sinusoidal noise; c~e— are notch result of noised signal in (a); f~h— are notch result of noised signal in (b)

Influence of different number of initial values of the third kind of initial condition on notch result
a—notch result of the noised earth impulse response in figure 7a; b—notch result of the noised earth impulse response in figure 7b

Removal of periodic noise in MTEM real field data
a—source current; b—received voltage; c—direct estimated earth impulse response (dashed line) and denoised earth impulse response (solid line)

Removal of periodic noise in MTEM real field data
dashed line is evaluated earth impulse response and solid line denoised earth impulse response

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