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.

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

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

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

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

Array Augmentation ITW ▫ 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

Array Augmentation ITW 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 † 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

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

Array Augmentation ITW BAZ simulation 180 m 40 m

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

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

Array Augmentation ITW ELVIS Experiment

Array Augmentation ITW Normalized ELVIS Results

Array Augmentation ITW 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 Numerical Augmentation

Array Augmentation ITW Numerical Augmentation

Array Augmentation ITW Numerical Augmentation

Array Augmentation ITW Discriminant Effectiveness 3-km 5-km

Array Augmentation ITW 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