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| | Abstract | | Fast Fourier Transform(FFT) has been widely used in data processing in magnetotelluric survey(MT). Although FFT assumes time series to be stationary, MT data is in general non-stationary since the source of MT is the abrupt electromagnetic fluctuation in the ionosphere. We think it may not be optimum to apply FFT method to obtain earth response for processing. We focus on a digital filter called pole on pedestal that extracts and amplifies the signal component of a specific frequency. We developed the data processing of MT data in time domain using this filter. In addition, it is important to select the segment included in the signal. We calculate cross correlations between filtered magnetic data at different sites, and select some segment in which the coherence among the sites has high values. In this way, we choose automatically the segment in the acquired time series. We apply the above-mentioned data processing in time domain to real MT survey data acquired at the Nankai trough. The range of the error-bars in our processing found much smaller than in the other conventional FFT method. We obtain more accurate response functions using novel data processing successfully. |
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