Martin Landrø (NTNU) and Jan Langhammer (TGS, Norway) article titled “Comparing the broadband acoustic frequency response of single, clustered, and arrays of marine air guns” has been published in the journal Geophysics.
Field data acquired from a seismic vessel by a seabed hydrophone is used to analyze the broadband response (10 Hz to 62.5 kHz) for various source configurations: single air guns, clustered air guns, and a full array consisting of 30 air guns. The various parts of the acoustic signal are analyzed in detail, and it is found that a high-frequency signal arriving prior to the main peak of a single air-gun signal most likely is caused by small vapor cavities collapsing at or close to the surface of the gun. This is confirmed by high-speed photographs taken when a small air gun is fired in a water tank. When the full array is used, a second type of cavitation signal is observed: ghost cavitation caused by acoustic stimulation by the negative pressure that is backscattered from the free surface. As this ghost signal from 30 different guns arrives at a specific location in the water, cavities might be formed, and they create a high-frequency acoustic signal.
Landrø, M.; Langhammer, J. (2020): Comparing the broadband acoustic frequency response of single, clustered, and arrays of marine air guns. Geophysics, vol. 85, no. 3 (May-June 2020); p. p27–P36, 14 figs. DOI: 10.1190/GEO2019-0768.1 [intranet]