Experimental Marine Vibrator With a Helmholtz Bubble Resonator in the Frequency Range 5–16 Hz

Abstract

The use of coherent broadband signals instead of explosive, high-intensity air-gun pulses is one potential way to reduce sound pressure and sound exposure levels in marine surveys. A coherent type of seismic source achieves a higher resolution, hence a sharper image of deep layers. In the upper-frequency range of seismic signals (higher than 16 Hz), marine vibrators can successfully apply the known acoustic technology of low-frequency underwater transducers. This technology is not as effective at low seismic frequencies. The slow progress in the development of this technology requires finding a different approach. An alternative would be to employ a gas-filled underwater cylindrical bubble resonator. A large gas-filled resonance bubble covered with an elastic membrane and driven by a blower with airflow controlled by a proportional valve provides significant power in the low-frequency range. We achieved a suitable broadband frequency response by designing a double resonance system consisting of a bubble and an internal Helmholtz gas acoustic resonator. Experimental tests were conducted at the Woods Hole Oceanographic Institution. This article provides an overview of engineering solutions considered in the design, including drivers, membranes, and methods of increasing efficiency.