Spectral Analysis of Airgun Pulses During Marine Seismic Reflection Surveys

Marine seismic reflection surveys use acoustic energy to image the structure of the seafloor. Broadband impulsive sound signals are generated by an array of airguns and recorded by single or multiple long horizontal hydrophone arrays towed behind a vessel. The high sound intensity of airgun signals can have impacts on marine mammals that communicate in the same frequency ranges. Characterizing the propagation of different spectral contents of airgun pulses is important for mitigating any potential impact of airgun pulses on marine mammals. This study takes a data-driven approach to characterize the sound levels at different one-third-octave bands radiated from a seismic source during a seismic reflection survey. Data utilized in this study are from the COAST (Cascadia Open-Access Seismic Transects) seismic reflection survey conducted with the R/V Langseth in July 2012. This experiment was conducted in the NE Pacific Ocean and spanned a wide range of water depths between 41 m to 9670 m. These measurements are used to perform a statistical spectral analysis of the airgun pulses propagating behind the seismic source.