2019_programme: EFFICIENT MODELING OF 3D ACOUSTIC PATHS TO IMPROVE SOURCE TRIANGULATION

• Session: 08. Comprehensive nuclear test-ban treaty monitoring
  Organiser(s): Haralabus George, Zampolli Mario, Nielsen Peter
• Lecture: EFFICIENT MODELING OF 3D ACOUSTIC PATHS TO IMPROVE SOURCE TRIANGULATION [invited]
  Paper ID: 947
  Author(s): Dall'Osto David
  Presenter: Dall'Osto David
  Presentation type: oral
  Abstract: Hydroacoustic signals recorded on the International Monitoring System (IMS) network have proven their capability to identify the origin of intense sound sources. A recent example is the detections CTBTO used to identify the search area where the lost Argentine submarine ARA San Juan was found [Nielsen et al. EGU2018-18559]. To triangulate a source, isochrones or surfaces of equal travel time are propagated from each station using a global model of ocean sound speed. With detections on two stations, the intersection of these isochrones forms a line due to an uncertain time of occurrence. With detections on 3 stations, the isochrones intersect at the source origin and furthermore establish a time of occurrence, noting that confidence in these are limited by the accuracy of the ocean model. Finding a detection on three stations however is not always possible, and as such azimuthal information garnered from coherent processing of the hydrophone triads that make up each IMS station provide another means to bound the triangulation. Furthermore, when additional arrivals distributed in azimuth can be associated with a particular source, e.g. delayed arrivals having a common spectral feature, these 3-dimensional paths can be modeled to establish additional isochrones, effectively adding “virtual” stations to improve triangulation. This is demonstrated using the bathymetrically refracted 3D features observed in two signals, one originated in the vicinity of the last known position of the ARA San Juan and the other a depth charge intentionally deployed two weeks later to assist in the search effort. Both signals have spectral and cepstral features allowing for unambiguous correlation of the arrivals recorded at two stations, HA10-Ascension and HA04-Crozet. This study concludes with an assessment of the accuracy, limitations and efficiency of 3D modeling techniques based on hybrid of rays, acoustic modes and the parabolic equation.
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• Corresponding author: Dr Dall'Osto David
  Affiliation: Applied Physics Laboratory at University of Washington, Seattle
  Country: United States
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