Time-domain denoising of time–frequency electromagnetic data*
Zhang Bi-Ming, Dai Shi-Kun, Jiang Qi-Yun , Yan Jian, and Li Guang
1.School of Computer and Communication, Hunan Institute of Engineering, Xiangtan, Hunan, 411104, China;
2.School of Geosciences and Info-Physics, Central South University, Changsha 410083,China;
3.Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring (Central South University), Ministry of Education, Changsha 410083,China;
4.School of Traffi c and Transportation Engineering, Central South University, Changsha 410075, China;
Abstract：
Time–frequency electromagnetic data contain frequency and transient electromagnetic information and can be used to determine the apparent resistivity both in the frequency and time domains. The observation data contains three types of noise: the harmonics interference at 50 Hz, high-frequency random noise, and low-frequency noise. We use frequency-domain bandstop fi ltering to remove the harmonics interference noise, segmentation and extension median fi ltering, and fi tting of fi xed extremes in empirical mode decomposition to remove the high-frequency and low-frequency noise, respectively; furthermore, we base the selection of median fi ltering window size on the variance and skewness coeffi cient of the data. We first remove the harmonics interference at 50 Hz, then the high-frequency noise, and fi nally the low-frequency noise. We test the proposed methodology by using theory and experiments, and we fi nd that the three types of noises are removed, the phase and amplitude information of the signal are maintained, and high-quality waveforms are obtained in the time domain.
2019, Vol. 16 
