Underwater Explosions as Acoustic Sources

The manner in which underwater explosions differ from low-amplitude point sources of sound is considered theoretically, especially effects due to cavitation near the sea surface. Some measured differences between the acoustic source levels of various size charges and some absolute charge source levels are given. These experimental results are presented for charge sizes between 0.002 and 50 lb, for charge depths from 7 to 60 fathoms, and for frequencies from 25 c/s to 6.4 kc/s. The results at a given depth are shown to obey a simple scaling law. Theoretical source levels are calculated by Fourier analysis of shot pressure-time curves reported by Arons. At high frequencies the theoretical spectral energies of the shock wave and the bubble pulses are simply added together, but at low frequencies it is necessary to take account of phase. In general there is very good agreement between the experimental and theoretical levels, and certain small discrepancies are explained in terms of bubble migration and related effects.