Spread Spectrum Sweep Strategy to Improve Operational Efficiency with Marine Vibrators

A spread spectrum sweep strategy is described that enables efficient and flexible opportunities for towed marine vibrator seismic surveys capable of generating arbitrary signals with full phase control over the frequency of interest to seismic imaging. Continuous source operation with orthogonal signal sequences enable the use of many simultaneous marine vibrator units whilst towing at efficient vessel speed. Post-survey, the desired shot point interval for the optimized imaging of a particular depth range can be optimized by combining varying numbers of sub-sequences: shallow targets are imaged with short sub-sweeps and therefore short shot point interval, and deeper targets are imaged with longer sub-sweeps, longer shot point interval, and higher signal amplitude by virtue of longer sweeps. Overall, this strategy may enable less marine vibrator units by comparison to that required to achieve a given sound pressure level (SPL) using conventional sweep strategies, have significantly lower environmental impact than any air gun source design, and enable greatly improved operational efficiency.