Impacts of seabed characteristics on short-range acoustic propagation in seismic surveys

Abstract

An abundance of marine seismic reflection surveys with publicly available datasets have been collected over the last several decades to study the composition of the seabed up to multiple kilometers below the sea floor. In these surveys, a loud impulsive airgun source broadcasts sound into the seabed and the reflections from the seafloor and seabed layers are measured on a long (up to ∼15 km) towed hydrophone array. In these surveys, both the shallow seabed layers (several hundred meters below the seafloor) and deeper layers (multiple kilometers below the seafloor) can significantly impact the acoustic field in the water column at close ranges. Experimental data have shown instances of sound exposure levels (SEL) at ranges between ∼8 and 15 km that exceeded levels predicted by cylindrical spreading models by nearly 15 dB. This work aims to use the abundance of seismic data available to explore the relationship between seabed and sub-seabed characteristics and the acoustic field in the water column. Inversion results that provide seabed sound speed profiles and reflection characteristics will be used to understand the seabed characteristics and its potential effects on SELs or sound pressure levels evaluated along the towed array. [Work supported by ONR.]