Three-dimensional propagation of seismic airgun signals in the Mississippi Canyon area of the Gulf of Mexico.

Ying-Tsong Lin

doi:10.1121/10.0003451

Abstract

Seismic airgun signals recorded on two hydrophone arrays during an oil and gas survey were analyzed for investigation of three-dimensional (3D) underwater sound propagation in the Mississippi Canyon area. A 3D numerical model with realistic seafloor and oceanographic inputs has been established to explain the intensified canyon focusing seen in the airgun signals received at one of the arrays. This study was under a passive acoustic monitoring program for establishing a current baseline of natural and anthropogenic sound sources and levels in the Gulf of Mexico. The reported investigation provides insight into the propagation effects affecting underwater soundscape in the area.

Highlights

Underwater sound propagation is subjected to the effects of bottom reflections and scattering, especially in submarine canyon areas1,2 where seafloor relief or terrain has strong spatial variability
This study provides an analysis of threedimensional (3D) propagation of seismic airgun signals in the Mississippi Canyon area and uses a 3D sound propagation numerical model for realistic underwater soundscape simulations
Most of the studies assumed two-dimensional (2D) sound propagation confined in the vertical planes originating from airgun sound sources, and one example is the analysis by DeRuiter et al.3 for investigating effects of surface mixed layer sound ducts in the Mississippi Canyon area

Summary

Introduction

Underwater sound propagation is subjected to the effects of bottom reflections and scattering, especially in submarine canyon areas where seafloor relief or terrain has strong spatial variability. Most of the studies assumed two-dimensional (2D) sound propagation confined in the vertical planes originating from airgun sound sources, and one example is the analysis by DeRuiter et al. for investigating effects of surface mixed layer sound ducts in the Mississippi Canyon area. They have shown that airgun pulse energy above a few hundred Hz can be trapped in a surface duct and expose marine mammals in that duct to signals at long distances. With a high-fidelity data assimilated ocean circulation model and a high resolution bathymetry grid, a 3D parabolic-equation (PE) approximation solver in a cylindrical coordinate system was employed to simulate sound propagation of the airgun signals and confirm the 3D propagation effects shown in the hydrophone data

Measurements

Models

Simulation results and discussions

Findings

Summary