Acoustic detection of microbubbles and particulate matter near the sea surface

Abstract

A pulse-echo system using an electrostatic transducer and steel reflector was operated over the frequency range 24-192 Kcps in the sea and in the laboratory. Excess attenuations from 0.15 to 1.1 db/M due to absorption and scattering by inhomogeneities were made over the full frequency range with a maximum error of less than 0.05 db/meter. Backscattering at sea was detected in the frequency range 24-60 Kcps with an average scattering cross-section per unit volume of 4.00 cm /m^ at a depth of 10 feet. Scattering was not detected abbve 60 Kcps. Variation of sound velocity with frequency was measured from 24-192 Kcps. The accuracy of these values was 0.03 percent for frequencies over 40 Kcps.