Radiated noise measurements in a harbor environment using a vertical array of omnidirectional hydrophones

Abstract

Measurement of the radiated noise of a ship or submerged vessel in shallow water is complicated by the presence of multiple surface and bottom reflections, requiring that environmental effects on propagation either be minimized in the measurement or accounted for in the result, or perhaps both. In a harbor environment, there are additional sources of reflection and noise that may degrade the ability to obtain meaningful measurements. The combination of multiple reflected paths, high background noise, and a possible inability to assume far-field behavior due to a shortened range present a significant challenge to acquiring high confidence measurements of the radiated acoustic field. This work presents preliminary results from a radiated noise measurement test conducted at the U.S. Navy's Acoustic Research Detachment in Bayview, Idaho during summer 2010. A line array of 14 equi-spaced omnidirectional hydrophones was deployed from a barge tied up adjacent to a moored test vessel to obtain radiated noise measurements. A series of test signals was also transmitted through a calibrated acoustic source deployed at various depths in the harbor to evaluate the effectiveness of vertical line array measurements in minimizing reflected path contributions and improving signal-to-noise ratio. Preliminary results and conclusions are presented. [Work sponsored by the Office of Naval Research, Code 331.]