Method of reducing harmonic interference while using overlapping source point seismic recording techniques

Abstract

Segmenting the spectral distribution of overlapped vibratory signals improves the efficiency of data acquisition while providing reduced harmonic distortion in the time zones of interest. Two identical sweep segments are used. Each sweep segment includes an earlier low frequency sweep and a later high frequency sweep, the individual sweeps having substantially no overlap in frequency except for tapering. The high frequency sweep in each pair starts before the end of the low frequency sweep with an overlap in time that is selected to avoid harmonics from the low frequency sweep. Correlation of the recorded signal separately with the low frequency sweep and the high frequency sweep gives data sets in which individual portions of the desired data are recoverable with the harmonic distortion largely separated from the desired data. The individual portions of the desired data are then spliced to give a broadband response of the earth. In an alternate embodiment of the invention, groundforce signals or accelerometer signals from the base plate or the reaction mass of the vibrators are measured and filters are derived relating the measured (reference) signals to a desired short duration wavelet. The derived filters are applied to the recorded data and the resulting filtered data sets are combined to give a broadband response of the earth.