Measurements of underwater noise from the RV Investigator

Australia's Marine National Facility, operated by CSIRO, has recently taken delivery of a new, $126 million, multi-purpose blue-water marine research vessel, RV Investigator. The ship is equipped with an extensive suite of active acoustic instrumentation that include an omnidirectional sonar, three multibeam echosounders, six split beam scientific echo sounders, two acoustic Doppler current profilers and a sub-bottom profiler. Permanently installed seismic compressors also prepare the ship to undertake geophysical survey missions. The ship has been designed to maximise the performance of these systems through innovative hull design to minimise air bubble entrainment under the acoustic transducers, and by reducing the underwater sound radiated from the ship through an innovative propulsion system, coupled with advanced isolation of vibration from the primary power generation machinery. This paper discusses some recent underwater noise measurements that were carried out in southern Tasmanian waters following Det Norske Veritas (DNV) guidelines in order to determine baseline underwater noise signatures for the vessel, and to characterise the noise performance of the various acoustic instruments. The baseline measurements obtained are compared to the ship's design criteria of DNV Silent-R and the expected background wind and thermal noise. The potential variability in vessel noise spectra obtained when following DNV noise measurement guidelines are also discussed.