Wang H.,Beijing University of Technology |
Wang H.,State Key Laboratory of Geological Processes and Mineral Resources |
Wei W.-B.,Beijing University of Technology |
Wei W.-B.,State Key Laboratory of Geological Processes and Mineral Resources |
And 17 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2014
Magnetotelluric (MT) sounding is one of useful electromagnetic (EM) exploration methods by applying propagation rules of natural EM fields. MT has been proved as an important geophysical method to explore fault structures and fluid movements, and for research of plate tectonics and continental dynamics. However, MT signal is typically non-stationary, weak and stochastic mixed with cultural noises which are intense, of wide bandwidth and complex components. Thus conventional methods for noise suppression in the frequency domain, such as robust estimation and remote reference technique, can only eliminate outliers and uncorrelated EM noise. In the case of strong noise, especially correlated ones, general processing methods are not satisfactory and MT sounding curves show obvious near-field effects. In this paper, based on the concepts of the signal and system, we discuss the relationship of MT time-series between the local and reference sites. We use the least square (LS) method to estimate the relationship by selecting some high SNR data as priori information, then calculate synthetic signal via the relationship and reference data, and replace noisy data of local channels with synthetic signal. The results of the test with high-quality field data acquired in Tibet show that the relationship is relatively stable for MT signal, which is independent of the distance and difference of electrical structures between local and reference sites, and only dependent on the priori data length. The simulation test shows that the synthetic data are considerably correlated with original signals with a coherence above 0.9, and the sounding curves are quite similar. Tests on practical MT data show that this technique can effectively remove local noise and suppress the near-field effects. At the same time, the resulting data keep slight natural signal. Finally, in terms of square wave noise which cannot be recognized by the variance ratio method, we propose a shift method. The result indicates that applying this method in the time domain together with remote reference technique in frequency, one can obtain credible data and smoothly varying curves even in a strongly noisy area. Instead of researching the characterization of complicated noises or separating MT signal from contaminated data, we utilize the clean data of the reference site to calculate synthetic signal.
Meng X.-H.,Geo detection Laboratory |
Liu G.-F.,Geo detection Laboratory |
Chen Z.-X.,Geo detection Laboratory |
Guo L.-H.,Geo detection Laboratory
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2012
It is a main research direction to outline the source distribution from the imaging result of the gravity or magnetic inversion based on rectangular units. Correlation imaging of gravity and magnetic is a method that calculates the normalized correlation of the anomaly of rectangular unit and acquired anomaly. The result can outline the properties distribution and earth structure. The correlation imaging method is characterized by fast computation, stability, and simplicity, but it results in values between -1 and 1 but not the real physical properties, and also can't use the prior geology information. In this paper, we proposed a method based on the correlation imaging of the residuals of acquired data and forward data based on a physical model; after some iterations, we get the physical property model. The model test verified the effectiveness of our method.