Time-Domain Spectral Induced Polarization Based on Pseudo-random Sequence
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Pure and Applied Geophysics
Time-Domain Spectral Induced Polarization Based on Pseudo-random Sequence MEI LI,1 WENBO WEI,1 WEIBIN LUO,1 and QINDONG XU1 Abstract—To reduce noise during electrical prospecting, we hereby propose a new method using correlation identification technology and conventional electrical exploration devices. A correlation operation can be carried out with the transmitted pseudo-random sequence and received time signal to suppress the random noise, and the time-domain impulse response and frequency response of the frequency domain of the underground media can be obtained. At the same time, using a dual Cole–Cole model to fit a complex resistivity spectrum, which is close to the frequency response, we can get a variety of induced polarization parameters and electromagnetic parameters of subsurface, which can provide more useful information for the exploration of mineral resources. This time domain prospecting method can effectively improve the efficiency of the spectral induced polarization method. In this article, we have carried out theoretical calculations and a simulation to prove the feasibility of such a method. Key words: Pseudo-random sequence, SIP, correlation identification technology, MTEM.
1. Introduction Conventional electrical prospecting is significantly limited by noise and low efficiency. The depletion of easily discovered mine reserves and other raw materials has triggered a renewed interest in alternative techniques for exploration. In electrical prospecting, the use of a pseudorandom signal as the transmitter signal source has been shown to improve the signal-to- noise ratio (SNR). As an example, the multi-transient electromagnetic system (MTEM) (ZIOLKOWSKI et al., 2006,
1
China University of Geosciences (Beijing), Beijing 100083, China. E-mail: [email protected]
2007, 2009) has become an established commercial system whose second and third generation equipment has been used to generate pseudo-random sequences instead of step signals, with significantly improved SNR. An MTEM system obtains the impulse responses of the subsurface by deconvolution of the transmitted and received signals. However, according to the correlation identification theory, the correlation operation of the received time sequence with a sent pseudo-random sequence can not only remove random noise to improve SNR, but also easily obtain the impulse response and frequency response of underground media (DUNCAN et al., 1980; QUINCY et al., 1980; LUO and LI, 2009). They employed electromagnetic methods in their approach to interpret the frequency response, whereas MTEM is based on DC resistivity inversion by the peak of the impulse response. In fact, the complex resistivity spectrum of the underground media can be deduced from its frequency response (PRASAD et al., 2010; LIU, 2010), but they did not explain how to obtain the complex resistivity spectrum from its frequency response. In this paper, we aim to propose a complex resistivity method based on the pseudo-random sequence, verify its feasibility wi
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