Fluids Seminar – July 15, 2019 – Dr. Shima Abadi

Analysis of Airgun Pulses During Marine Seismic Reflection Surveys

Prof. Shima Abadi
Engineering and Mathematics, University of Washington

When: July 15, 2019 | 2-3 PM
Where: CEME 2202 | 6250 Applied Science Lane

 

Abstract: 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 those frequencies. To better mitigate against those impacts, safety radii are defined to ensure animals are not exposed to high sound levels. Establishing safety radii strongly depends on transmission loss (TL) in the ocean environment, i.e., the acoustic energy loss between the airguns and the receivers. In this talk, I use both simulation and experiment to characterize the transmission loss, and hence the sound levels radiated from a seismic source, in the vicinity of a seismic survey. The experimental data utilized in this study are from the COAST (Cascadia Open-Access Seismic Transects) seismic reflection survey conducted in the NE Pacific Ocean in summer 2012. The seismic source array used on this cruise consisted of 36 airguns with a total volume of 6600 cubic inches. At each shot, 16.382-second data with a sampling rate of 500 Hz were recorded by an 8 km hydrophone array consisted of 636 hydrophone groups that were towed between 258.5 m and 8418.3 m behind the seismic source array. This study will use over 2 million shots spanning a wide range of water depths between 41.8 m to 9670.2 m to describe the differences between the propagation of airgun pulses in shallow water and deep water.

 

Biography: Shima Abadi received the B.S. degree in Mechanical Engineering from the University of Tehran, Iran in 2008, the M.S. degree in Mechanical Engineering from the University of Michigan in 2010, and the M.S. degree in Applied Mathematics and the Ph.D. degree in Mechanical Engineering from the University of Michigan in 2013. She was a Postdoctoral Research Scientist at the Lamont-Doherty Earth Observatory at the Columbia University and a Visiting Scientist at the School of Oceanography at the University of Washington from 2013 to 2015. She is currently an Assistant Professor in Mechanical Engineering and an Affiliate Assistant Professor in Electrical Engineering at the University of Washington. Her research primarily focuses on acoustical signal processing in ocean sciences. She worked on a broad range of topics such as blind deconvolution, sound source localization, direction-of-arrival (DOA) estimation, acoustical imaging, and animal bioacoustics. Dr. Abadi has received two best paper awards from the Acoustical Society of America in 2009 and 2013. She is currently working on mitigating seismic airgun noise, analyzing ocean ambient noise, and developing graph signal processing algorithms for analyzing data collected by large, dynamic, and irregular underwater networks.