At-sea measurements of sound penetration into sediments using a buried vertical synthetic array

Abstract

At-sea measurements were conducted to understand the propagation of sound into sediments. These investigations used a new, buried vertical synthetic array system developed and built at the Naval Research Laboratory. The design of this at-sea system is based on a system developed for laboratory experiments that utilized a two-dimensional synthetic array technique [J. Acoust. Soc. Am. 107 (2000)]. For the measurements reported here, the hydrophone was water-jetted into the sediment to a depth of 2 m. Once buried, the hydrophone was mounted to a vertical robotics stage that pulled the hydrophone up in 1-cm increments. A spherical source, positioned 50 cm above the interface, was used to ensonify the sediment. The ensonification angle was varied by changing the horizontal distance of the source from the insertion point. In this manner, several measurements were made with ensonification angles above and below the critical angle. In addition, the enhancement of sound penetration due to interface roughness was investigated. This new system, along with the results of the measurements, will be discussed. [Work supported by ONR.]