Use of a Hydroacoustic Transducer in Continuous Seismic Profiling

Abstract

The hydroacoustic transducer is an acoustic radiator actuated by an electrohydraulic positioning servo. It was used during April 1963 as a low-frequency, broad-band source in continuous geophysical profiling experiments aboard Hudson Laboratories research vessel J. W. GIBBS (T-AGOR-1). The transducer has a 2-ft diam acoustic piston driven by a 14-in.-sq. hydraulic ram, fed through 200 ft of hydraulic lines from a 35 GPM, 2000- to 3500-psi, shipborne hydraulic power supply. The transducer controller consisted essentially of a 10-W electronic servoamplifier fed by various audio signals. The experiment is similar to that described by Clay and Liang [Geophysics 27, 786–795 (1962)]. In this experiment, most of the data were obtained with either 1-sec 100-cps bandwidth chirps or noise pulses within the total range of 80–400 cps. Short 250-cps pings were also used. The signal returns were processed with a polarity correlator. In this system, one compresses the coded pulse of relatively long time duration and low amplitude into a short pulse of high amplitude. In the 200- to 300-cps range, the radiated pulse is estimated to be about 900 J energy and 500 J in the 100- to 200-cps frequency range. Seismic profiles were made in the Hatteras Abyssal Plain area in water depths of 3000 f and subbottom penetrations of 34- to 114-sec travel time were recorded. Two and three subbottom reflections were often observed. [Hudson Laboratories, Columbia University Informal Documentation No. 33. This work was supported by the Raytheon Company and the U. S. Office of Naval Research.]