Underwater radiated noise of the NOAA ship Oscar Dyson

The NOAA Ship OSCAR DYSON is the First-in-Class fisheries research vessel designed and built for the National Oceanic and Atmospheric Administration (NOAA) for fish stock assessment. One of its most important contractual requirements was to achieve an underwater noise limit established by the International Council for the Exploration of the Seas (ICES). The underwater noise limit has been specified by ICES over too large a frequency range and too small a resolution to allow for measurements with commercial grade test equipment. Modifications to the limit were made by NOAA which allowed the authors to develop a simple, deployable underwater measurement system. This system was then used to measure underwater noise from the OSCAR DYSON during sea trials in the Gulf of Mexico. The system consisted of a hydrophone array, signal conditioning and data acquisition hardware. The distance between the hydrophone array and the vessel must also be measured during the survey with the vessel in the acoustic far-field. Results from the far-field noise measurements were compiled and then compared to the ICES specification requirements. Self-noise from permanently mounted hydrophones in the hull were also measured during the survey. Finally, a comparison between the commercial system used by the authors and subsequent measurements performed by the U.S. Navy at their acoustic underwater test facility is made. These show good agreement at all but the lowest frequencies.