Survey of nonexplosive sources for acoustic propagation measurements

Abstract

Since the mid 1940's explosive charges have been widely used by offshore seismic exploration companies, by the U. S. Navy, and by other groups to generate high‐intensity acoustic pulses for seismic and sonar‐related activities. In the late 1950's offshore exploration groups began to develop alternate energy sources, and in the mid 1960's a number of non‐explosive impulse and cw marine sound sources were introduced and soon dominated the offshore exploration field. Despite their relatively low‐energy levels, these sources have since been tailored to reproducibly generate acoustic spectra concentrated in the range below 100 Hz at efficiency levels that have allowed them to completely replace shallow‐detonated explosives. This report briefly describes important characteristics of four classes of nonexplosive acoustic impulse sources developed for offshore seismic exploration purposes and compares their acoustic signatures with those of explosive SUS charges used in sonar propagation studies. The total energy levels of SUS and several nonexplosive impulse sources are compared and acoustic levels, bubble pulse, and the spectral characteristics of the signatures are discussed and methods for defining and controlling these characteristics are briefly described. [Work supported by ONR/LRAPP.]