The Processing of Rectangular Interferences on Magnetotelluric Sounding Data Based on Hilbert-Huang Transform

Observation of natural electromagnetic field shows that rectangular interferences leads to that the signals fluctuate violently. As a result, the sounding curves (apparent resistivity or phase curves) are distorted. The following analysis and processing are seriously influenced. According to the change features of rectangular interference in time domain, Hilbert-Huang transform (HHT) was applied in this study to suppress rectangular interferences. First, the signal was carried out empirical mode decomposition (EMD) to obtain intrinsic mode functions (IMF) of different orders; then the overall instantaneous frequency of IMF in each order was calculated using median deviation. Next, the IMFs in the orders which contain noises were screened out by comparing the overall instantaneous frequency of IMF frequency domain in each order. And those IMFs were set to be zero; at last, the signals were reconstructed using EMD. The measured data indicated that before and after construction, the signals present only little energy loss, high correlativity. Besides, the reconstructed signals were as precise as that of the original ones with high precision and could effectively eliminate the interferences.