A new type of airgun has been developed that has a greatly reduced acoustic output at high frequencies. The high frequencies originate from the rising edge of the primary pulse; the reduction has been achieved by a significant redesign of the mechanism that controls the air release. The environmental benefit of such a source is demonstrated and it is shown that the pulse-shape within the seismic imaging frequency range is substantially unaffected. The recently released 'Draft Guidance for Assessing the Effects of Anthropogenic Sound' from the National Oceanic and Atmospheric Administration (NOAA, 2013) with its more stringent requirements on high-frequency sound has drawn this issue into a sharper focus.

We have developed a new airgun that optimizes the useful seismic output while limiting any environmental effects from unnecessary high-frequency emissions. We regulate the output at the air-gun's ports by controlling the motion of the mechanical components that release air from an internal chamber. Our design process is based on advanced fluid-dynamics simulation to optimize acoustic performance, and mechanical finite-element simulation to ensure structural robustness. This is validated by physical tests to calibrate the models, improve reliability, and characterize the final acoustic performance. Having carried out extensive testing on prototypes, we plan to introduce the airgun into arrays for a commercial seismic survey.

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