The Suppression of Powerline Noise for TEM with Coded Source Based on Independent Component Analysis

Powerline noise is one of the most common contaminating types of the observed transient electromagnetic signal. For the conventional TEM method using the bipolar square wave as transmitter waveform, synchronous sampling is the main technology for powerline noise suppression, and notching filtering is sometimes used also. When the transmitter wave has been encoded based on pseudo-random binary sequence, it has proven difficult to achieve the effect by using the above-mentioned conventional methods for the suppression of powerline noise. This is due to the fact that the duration of each logic states of the pseudo-coded transmitter waveform is normally inconsistent. In this study, a method for the suppression of powerline noise is proposed, which is based on the independent component analysis method (ICA). In order to introduce the observation and processing details of this method more clearly, we attempt to apply this method to the time-domain electromagnetic method with coded source researched and developed by the institute of geology and geophysics of Chinese academy of sciences on the basis of the MTEM method. In terms of specific processes, the electrical measurements need to be simultaneously observed in the inline and crossline directions firstly, and then the data will be input into the processing procedures based on ICA method to realize the effective separation of the powerline noise and the useful signals. The processing results of the simulation data and field data show that the method proposed in this paper can suppress the powerline noise effectively, and the processing results build a good data foundation for the subsequent processing.