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 The recently released 'Draft Guidance for Assessing the Effects of Anthropogenic Sound' from the National Oceanic and Atmospheric Administration (NOAA, 2013) with its more stringent requirements on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.

A seismic vibrator generates seismic and acoustic noise as soon as it is pressured up and located in the proximity of a recording spread. The noise in the seismic bandwidth is more critical in vibroseis surveys where a large number of vibrators are used as in the case of simultaneous acquisitions. The noise in the acoustic bandwidth is particularly important when the survey takes place in populated areas. We carried out a seismo-acoustic experiment to characterize these noises. We present the results obtained while the vibrator is pressured up but not sweeping, with the baseplate in contact or not with the ground. We demonstrate that several monochromatic noise components can be related to the cooling and exhaust systems. We also show the effects in the seismic and acoustic bandwidths of modifications to the cooling and exhaust systems.

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