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, Bermuda5 November 2008 This presentation does not necessarily reflect the policies or views of the United States Government.

2. Array Augmentation ITW 20082 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.

3. Array Augmentation ITW 20083 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

4. Array Augmentation ITW 20084 The IMS Infrasound Problem ▫ Too many signals  excessive false alarms ▫ Raise detection threshold  missed event

5. Array Augmentation ITW 20085 The IMS Infrasound Problem ▫ Too many signals  excessive false alarms ▫ Raise detection threshold  missed event

6. Array Augmentation ITW 20086 The IMS Infrasound Problem ▫ Too many signals  excessive false alarms ▫ Raise detection threshold  missed event

7. Array Augmentation ITW 20087 The IMS Infrasound Problem ▫ Too many signals  excessive false alarms ▫ Raise detection threshold  missed event ▫ Develop a near-field discriminant

8. Array Augmentation ITW 20088 ▫ Near-field discriminant ▫ Precise geolocation via TDOA ▫ ITW 2005 Tahiti (single arrays) ▫ ITW 2006 Fairbanks (meta-arrays) ▫ ELVIS 2007 Previous Work Szuberla & Olson, JASA, 115(1), 2004 Szuberla, et al., JASA-EL, 120(3), 2006

9. Array Augmentation ITW 20089 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)

10. Array Augmentation ITW 200810 † US Patent Pending 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

11. Array Augmentation ITW 200811 BAZ (plane wave) sensors source y x Back Azimuth ,  v t

12. Array Augmentation ITW 200812 BAZ simulation 180 m 40 m

13. Array Augmentation ITW 200813 srcLoc (spacetime approach) t arrivals source sensors y x Localization: r, ,  v t

14. Array Augmentation ITW 200814 BAZ vs. srcLoc simulation 19 m 3 m

15. Array Augmentation ITW 200815 ELVIS Experiment

16. Array Augmentation ITW 200816 Normalized ELVIS Results

17. Array Augmentation ITW 200817 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

18. Array Augmentation ITW 200818 Numerical Augmentation

19. Array Augmentation ITW 200819 Numerical Augmentation

20. Array Augmentation ITW 200820 Numerical Augmentation

21. Array Augmentation ITW 200821 Discriminant Effectiveness 3-km 5-km

22. Array Augmentation ITW 200822 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