Derivations of transfer functions for estimating ship underwater radiated noise from onboard vibrations

The adverse impacts of underwater radiated noise (URN) from marine vessels on marine life are increasingly recognized. URN estimation and subsequent monitoring could be used to track URN and take measures to reduce it in sensitive environments (e.g., a marine life protected area). Two common radiated noise power approximations and two empirical methods are assessed for URN estimation. The assessments were carried out by testing the methods on data from acoustic range measurements of the ORCA-class Patrol Craft Training Moose from the Royal Canadian Navy and a DAMEN Combi freighter. The common approximations are called equivalent radiated power and a method based on the volume velocity; both estimate URN directly from onboard accelerometer measurements. The empirical methods are based on the correlations of onboard vibrations with measured URN, from which transfer functions are derived. Acoustic range measurements are divided into training and testing runs. The correlations are applied to the training runs to conceive the transfer functions. The transfer functions are then used to estimate SL from onboard vibrations for the testing runs for validation purposes.