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 filtering to remove the harmonics interference noise, segmentation and extension median filtering, and fitting of fixed extremes in empirical mode decomposition to remove the high-frequency and low-frequency noise, respectively; furthermore, we base the selection of median filtering window size on the variance and skewness coefficient of the data. We first remove the harmonics interference at 50 Hz, then the high-frequency noise, and finally the low-frequency noise. We test the proposed methodology by using theory and experiments, and we find 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.

中文翻译：

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时间-频率电磁数据的时域去噪

时频电磁数据包含频率和瞬态电磁信息，可用于确定频域和时域的视在电阻率。观测数据包含三种类型的噪声：50 Hz的谐波干扰，高频随机噪声和低频噪声。我们使用频域带阻滤波来去除谐波干扰噪声，分段和扩展中值滤波，以及在经验模式分解中固定极值的拟合来分别去除高频噪声和低频噪声；此外，我们根据数据的方差和偏度系数选择中值滤波窗口大小。我们首先消除50 Hz的谐波干扰，然后消除高频噪声，最后消除低频噪声。