Efficiency of a Cluster of Marine Seismic Sources

A gas-filled bubble resonator with an internal sound resonance system is one of the simplest ways to create a broadband source of low and ultra-low frequency seismic waves. The internal acoustic resonant structure can change the frequency response of the entire source and expand its bandwidth. An internal Helmholtz resonator convert the narrow-band underwater bubble resonator to a double resonant system with a wide frequency bandwidth. A high-power seismic low-frequency source must also be very efficient. Low efficiency creates technical problems when transmitting electricity from a ship to an underwater seismic source. The cost of a towing cable system can be comparable to the source itself. There are three approaches to improving the efficiency of underwater low-frequency sound sources covering a large frequency band: using a tunable high-quality resonator; increasing the radiation aperture and using clusters of small sources. The low efficiency of practical underwater bubble resonators makes the first approach useless. Sound sources with large aperture are heavy, difficult to deploy and expensive in exploitation. In this study, we focus on a small (16–32 element) source array constructed from commercially available off-the-shelf components, with each source size and price comparable to an air gun. The main tool of this study was the finite element analysis of the source array, considering the internal structure of the sound sources used. Studies have confirmed that at a distance between sources of ~2 m they operate independently. This means that when they are combined, they add up not power, but pressure, and the efficiency of combining the system increases in proportion to the number of sources in the array. The resulting array of 16–32 sources will have sufficiently high efficiency for many practical applications.