The localization of marine mammals is important for biological studies and for assessments of the impact of anthropogenic activities on the marine environment. Passive acoustic monitoring (PAM) has become an increasingly popular method for localizing certain marine mammal species that are acoustically active. We have used both vertical and horizontal hydrophone arrays to find baleen whale ranges.
- PAM using a vertical hydrophone array
In this study, mode-based synthetic time reversal (STR) method is used to estimate the range of broadband (50–500 Hz) bowhead whale calls in a shallow waveguide using a vertical array of hydrophones. STR results compared with the triangulation results obtained from using a full horizontally-distributed array (Directional Autonomous Seafloor Acoustic Recorders-DASARs) and even displayed more precision for calls originating well outside the distributed array boundaries. This method is applied to an experimental data set and results are presented here.
- PAM using a horizontal seismic streamer array
Marine mammals use sound for their important life functions such as communicating, navigating, and finding food or a mate. Ocean noise pollution has increased greatly in recent years due to human activities in the ocean and seismic surveys are one of the most common high source-level anthropogenic sounds in the ocean. Seismic reflection surveys use low frequency acoustic energy to image the structure of the seafloor, with seismic arrays designed to focus as much of the sound as possible downward to maximize the energy penetrating the solid earth. Since seismic surveys use low frequency sound to image structure beneath the seafloor, the potential impact on baleen whales that communicate in the same frequency range may be particularly significant. The localization of whales is important for assessing the impact of seismic activities on the marine environment. The purpose of this study is to develop and evaluate a technique, called travel time residual (TTR), to locate a low-frequency underwater sound source using an 8-km long multi-channel horizontal array of sensors and expand it to whale localization in the vicinity of seismic surveys. The travel time residual method is a grid-search technique that estimates the two-dimensional horizontal location of a whale call using data recorded by seismic streamers. Results show that this method has the potential to be utilized not only for improving mitigation processes, but also for studying baleen whale behavior within the vicinity of seismic operations.
For more information, please see our publications:
- Shima Abadi, Maya Tolstoy, William Wilcock, (2017) “Ranging baleen whale calls using towed hydrophone arrays during seismic reflection surveys and studying effectiveness of a mitigation process”, PLoSONE 12(2): e0171115. doi:10.1371/journal.pone.0171115 [Link].
- Shima H. Abadi, William S. D. Wilcock, Maya Tolstoy, Timothy J. Crone, Suzanne M. Carbotte, (2015) “Sound source localization using data recorded by hydrophone streamers during seismic surveys”, Journal of the Acoustical Society of America, Vol. 138, Issue 6, [Link].