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Augmentation of IMS Infrasound Arrays for Near-field Clutter Reduction

Augmentation of IMS Infrasound Arrays for Near-field Clutter Reduction. Curt A. L. Szuberla, John V. Olson and Kenneth M. Arnoult, Jr. Wilson Infrasound Observatories Geophysical Institute, University of Alaska Fairbanks. Presented at the Infrasound Technology Workshop

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Augmentation of IMS Infrasound Arrays for Near-field Clutter Reduction

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  1. Augmentation of IMS Infrasound Arrays for Near-field Clutter Reduction Curt A. L. Szuberla, John V. Olson and Kenneth M. Arnoult, Jr. Wilson Infrasound Observatories Geophysical Institute, University of Alaska Fairbanks Presented at the Infrasound Technology Workshop Hamilton Parish, Bermuda 5 November 2008 This presentation does not necessarily reflect the policies or views of the United States Government.

  2. Abstract The analysis of data recorded at IMS infrasound arrays is complicated by the presence of near-field clutter, both from anthropogenic and geophysical sources. Ideally, the IDC would like to exclude events that arise from within ~100 km of an array from its analysis pipelines. Previous work by our group made use of a signal processing technique to identify signal sources arising from within about ~20 km of a single IMS array, using only that array for the identification. Subsequently, we have explored the use of several, small arrays for precise localization of infrasound sources. This work has begun to be extended to the augmentation of an existing IMS array in an effort to push that near-field identification zone farther out. We present an introduction to this work and preliminary results of numerical simulations. Array Augmentation • ITW 2008

  3. The IMS Infrasound Problem • Principal IMS task: record far-field events ≥ 1kT • Infrasound stations operate in noise: natural & manmade • Ubiquitous near-field sources: high spatiotemporal coherence Array Augmentation • ITW 2008

  4. The IMS Infrasound Problem • Too many signals  excessive false alarms • Raise detection threshold  missed event Array Augmentation • ITW 2008

  5. The IMS Infrasound Problem • Too many signals  excessive false alarms • Raise detection threshold  missed event Array Augmentation • ITW 2008

  6. The IMS Infrasound Problem • Too many signals  excessive false alarms • Raise detection threshold  missed event Array Augmentation • ITW 2008

  7. The IMS Infrasound Problem • Too many signals  excessive false alarms • Raise detection threshold  missed event • Develop a near-field discriminant Array Augmentation • ITW 2008

  8. Szuberla & Olson, JASA, 115(1), 2004 Szuberla, et al., JASA-EL, 120(3), 2006 Previous Work • Near-field discriminant • Precise geolocation via TDOA • ITW 2005 Tahiti (single arrays) • ITW 2006 Fairbanks (meta-arrays) • ELVIS 2007 Array Augmentation • ITW 2008

  9. TDOA: Eases Constraints • Amplitude independent  no r -1 problems (vegetation & terrain) • Functional form of signal  need only spatiotemporal correlation • Efficient linear algebraic calculations • Robust estimation via simple pre-processing (model tolerant) Array Augmentation • ITW 2008

  10. Geolocation Primer • Conventional geolocation (BAZ) • Data fusion • Multiple arrays & back azimuths • UAF technique (srcLoc)† • TDOA approach • Single meta-array • Predicted performance gain • Simple, albeit unrealistic, model Array Augmentation • ITW 2008 †US Patent Pending

  11. y Back Azimuth  ,vt x BAZ (plane wave) source sensors Array Augmentation • ITW 2008

  12. 180 m 40 m BAZ simulation Array Augmentation • ITW 2008

  13. t Localization: r,,vt y x srcLoc (spacetime approach) arrivals source sensors Array Augmentation • ITW 2008

  14. 3 m 19 m BAZ vs. srcLoc simulation Array Augmentation • ITW 2008

  15. ELVIS Experiment Array Augmentation • ITW 2008

  16. Normalized ELVIS Results Array Augmentation • ITW 2008

  17. Near-field Discrimination II • Precise localization is attainable • srcLoc • discrete, distended arrays (meta-array) • Limitations • source distance • meta-aperture • Why not augment an IMS array • imprecise localization • upper bound  effective discriminant Array Augmentation • ITW 2008

  18. Numerical Augmentation Array Augmentation • ITW 2008

  19. Numerical Augmentation Array Augmentation • ITW 2008

  20. Numerical Augmentation Array Augmentation • ITW 2008

  21. Discriminant Effectiveness 5-km 3-km Array Augmentation • ITW 2008

  22. Future Work • Numerical work at UAF • Atmospheric modeling at UM • Fieldwork & validation • UM research array(s) • UAF IMS array(s) • Determine correlation standoff limit • Refine model assumptions Array Augmentation • ITW 2008

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