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Utilizing CTBT Hydroacoustic Stations
Figure 9. Search map showing data from Iridium telecommunication satellite fixes (blue circles) and various modeled locations based on the recorded impulse. A combination of seismic and hydroacoustic detections were used and predicted the ARA San Juan location (red star) to within 8 nautical miles. Image provided by Ocean Infinity.
within 1/1,000 of the propagation distance, was possible because the IMS network requires such precision to accom- plish its mission, i.e., detecting and triangulating a nuclear explosion within an area no larger than 1,000 km2 (Protocol to the CTBT, Part IIA). Triangulation of an unknown source requires at least three arrivals (the third arrival used in the triangulation was reported by the CTBTO in 2017; see Figure 9) was on a land-based seismic station. A pure hydroacous- tic triangulation of the San Juan is possible if 3-D paths are considered. With the location of the San Juan now known, it is a dataset to baseline alternative methods of locating such signals of unknown origin.
Ultimately, error in triangulation depends on how well the actual ocean climate is characterized. Although yet to be implemented in any systematic way, the real-time data collec- tion of the IMS network makes it possible to deploy a source and rapidly assess climatic anomalies such as those fueling the powerful thermal engine of a destructive hurricane. In fact, an example of this rapid assessment came two weeks after the San Juan went missing; an impulsive source (depth charge) was deployed to confirm the propagation characteristics. Beyond the critical mission of the IMS network (detections of nuclear explosions), the data it has collected and continues to collect
can be used for other important purposes. Tsunami detection and enhanced early warning and geolocation of lost subma- rines, ships, and planes as well as assessments of cetacean populations and other marine life all can be derived from analyzing IMS data. The possibilities for the productive use of the historical and real-time IMS data are limitless.
References
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Dall’Osto, D. R. (2019). Source triangulation utilizing three-dimensional arrivals: Application to the search for the ARA San Juan submarine. The Journal of the Acoustical Society of America 146(3), 2104-2112.
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Villán, J. L. (2019). The tragic loss of ARA San Juan. Proceedings of the U.S. Naval Institute 45, 1393.
Worcester, P. F., Munk, W. H., and Spindel, R. C. (2005). Acoustic remote sensing of ocean gyres. Acoustics Today 1(1), 11-17. https://doi.org/10.1121/1.2961121.
BioSketch
David R. Dall’Osto received his PhD in mechanical engineering from the Uni- versity of Washington (Seattle) in 2013. Currently, he is a senior research scien- tist and engineer at the Applied Physics Laboratory, University of Washington. His research focus includes modeling
and measurement of acoustic vector intensity in the ocean and atmosphere on both short-range and global scales. His work with the Comprehensive Nuclear Test Ban Treaty (CTBT) data originates from a detective role, and he has found great satisfaction in applying forensic acoustics to resolve ocean mysteries.
28 | Acoustics Today | Winter 2019