Impulsive underwater sound from air guns

Abstract

The sound impulse radiated from underwater detonation of an air gun has a peaked energy spectrum, with the peak centered on the fundamental frequency of air‐bubble oscillation. Measurements of the sound impulses are reported for air guns having chamber volumes extending from 120 to 1650 in.3, chamber pressures extending from 1000 to 4000 psi, and detonation depths extending from 50 to 1400 ft. For each combination of parameters, the dominant contribution to sound energy is made by frequency components associated with the fundamental bubble oscillation frequency. Values are presented for the sound energy source levels, the fundamental frequencies, and the bandwidths of sound impulses covering the entire range of measurement variables. The fundamental frequency of air gun impulses is not found to depend upon depth and upon initial stored energy in the same way that that from impulse explosives does. Also unlike from impulse explosives, the radiated sound energy depends significantly on depth, being approximately proportional to the inverse‐square power of depth. Some hypotheses are given to explain the differences between air gun and explosive sound impulses. [Research sponsored by DARPA.]