Crosstalk-free Simultaneous Acquisition by Arbitrary Sweeps with Amplitude Modulation

Simultaneous source technique has been increasingly considered as the number of shots increases significantly on recent seismic surveys. We introduce an approach of crosstalk-free simultaneous acquisition using amplitude modulation (AM). Sweep sources are usually repeated many times for enhancing signal-to-noise ratio (S/N). If sweep waveform is accurately repeated, the source signal exists at limited frequency “channels” compared with discrete total-frequency samples determined by the sampling rate and total time length. The idea of the AM method is to utilize empty channels assigned for other shots, and thus the multiple shot data can be completely decomposed. Our approach can simultaneously produce N-individual shot data by 2N-1 repeated sweeps. Also, AM-applied data after cross-correlation are equivalent to the original data as, in our method, source wavelet after auto-correlation does not change by amplitude modulation. We performed a field test using amplitude-variable piezoelectric source for crosshole configuration. We excited 6 shots simultaneously using AM-applied pseudo-random sweep. The field results confirmed that shot data are decomposed completely and that shot gather obtained by simultaneous sources has no observable difference with that obtained by single source. This method should contribute to efficient high S/N data acquisition using piezoelectric, vibroseis source or acoustic and radar surveys.