Source level predictions of surface ships using seabed characterization in the New England Mudpatch from viscous grain shearing model

Abstract

Acoustic inferences from remote sensing of surface ship radiated noise in bottom-limited ocean environments are difficult due to a generally unknown geoacoustic structure of the seabed. The idea here is to first calibrate an acoustic sensing system by estimating geoacoustic parameter values by utilizing controlled sources with known levels. Then, the acoustic field that results from a surface ship is utilized to estimate the ship source levels where the transmission loss is constructed based on the previous estimate of the seabed parameterization and measurements of the sound speed profile at the time that the ship noise measurements were made. This concept was tested with acoustic data collected on two vertical line arrays (VLAs) during the Seabed Characterization Experiment in the New England Mudpatch during April 2017, in 75 m of water. The acoustic field was produced with a controlled source radiating in the 1.5–4 kHz band. A maximum entropy method provided estimates of viscous grain shearing (VGS) model parameter values. Then, using this VGS parameterization, ship source levels as a function of aspect and frequency out to about 3 kHz were extracted for the RV Endeavor and several merchant ships passing near the VLAs. [Work supported by ONR N00014-16-C-3065.]