Hum Filter: Power-line Noise Eliminator for Shallow Seismic Data

A unique filtering approach designed to eliminating power-line noise on shallow seismic data without affecting the frequency content of signal provides a powerful harmonic noise suppression tool for data acquired with modern large dynamic range recording systems. Amplitudes and phases of sinusoids (functions of power-line noise) present before the first arrivals can be estimated using the Levenberg-Marquardt (L-M) method. Initial amplitudes of sinusoids are determined in the frequency domain using fast Fourier transform (FFT) methods while initial phases are obtained by time domain correlation. Well-defined initial values guarantee convergence of the L-M method. Modeling results suggest the relative error of initial estimates are less than 50 percent. Calculation efficiency is achieved by simplifying the L-M solution using the singular value decomposition (SVD) technique. The approach can handle cases where power-line noise with frequencies of 60 Hz and/or its multiples exist simultaneously. Once determined, the amplitudes and phases of sinusoids can be directly subtracted from the raw data. Recorded frequencies of high-resolution shallow seismic surveys generally range from 30 to 300 Hz. Power-line noise (60 Hz) and its multiples (120 Hz, 180 Hz, and 240 Hz, etc.) are within the optimum frequency range. This filtering technique only removes harmonic noise and does not alter the spectra of signal. Real data examples demonstrate the efficiency and accuracy of this method when implemented on a normal shallow seismic data processing flow.