SUBTRACTION OF POWERLINE HARMONICS FROM GEOPHYSICAL RECORDS

Two processing techniques for suppressing stationary powerline noise in a time series are presented. Both techniques involve subtracting an estimate of the harmonic component. Unlike notch filters, they are capable of suppressing numerous frequencies without distorting or attenuating the signal of interest. Reductions of up to 45 dB in the ambient noise level have been obtained by using these methods to subtract up to 25 harmonics of 60 Hz from recordings of electric fields in the earth. -from Authors