Estimating Free Field, Far Field Radiated Noise Source Levels from Measurements Acquired in a Harbor Environment.

摘要

The radiated noise of ships or other underwater sources are typically characterized in terms of a far-field, plane-wave equivalent source level based on measurements assumed to have been acquired m a free field environment such as a deep water test range. Measurement ol ship noise in a harbor environment. where multiple reflections, high background noise and short propagation paths are the norm, violates the conditions that assume the ship is a radiating simple source. Careful analysis is required to arrive at a valid estimate of far-field, free-field source levels from such measurements. This work presents results from a test conducted at the US Navy Acoustic Research Detachment in Bayview, Idaho during summers 2010 and 2011. A line of omnidirectional hydrophones was deployed from a barge adjacent to a moored test vessel to obtain radiated noise measurements from several shipboard sources. A series ol test signals was also transmitted through calibrated acoustic sources to evaluate the effectiveness of post processing techniques, as well as line array beamforming, in minimizing reflected path contributions and improving signal-to-noise ratio. Methods of estimating far-field, free field equivalent source levels based on these measurements are presented.