Acoustic modeling of ducted propagation in the New England Mud Patch

Abstract

Experiments were conducted on the New England Mud Patch in 2017, 2021, and 2022. The 2017 Seabed Characterization Experiment (SBCEX17) utilized Signal Underwater Sound (SUS) charges, model Mk64, to produce an impulsive acoustic waveform. However, recent work in 2022 has additionally utilized the Rupture Induced Underwater Sound Source (RIUSS) to produce a high-amplitude, broadband waveform with minimal bubble oscillations. Results from these experiments suggested the presence of a surficial layer of mud with a sound speed lower than that of the underlying mud and overlying water. The SBCEX22 experiment included the deployment of nine RIUSS devices and the use of Ocean Bottom Recorders (OBX) to measure the acoustic pressure and three components of particle velocity at range of about 1 km. Conductivity, temperature, and depth measurements from CTD surveys were taken from several locations around the mud patch and used to generate sound speed profiles. These were input into the RAM parabolic equation model to analyze the effect of the sound speed in mud on propagation. Results from the RAM modeling indicates that at mid-frequencies (1-3 kHz) the lower sound speed at the top of the mud layer creates a duct where the transmission loss is reduced.