Augmentation of IMS Infrasound Arrays for Near-field

Clutter Reduction

Curt A. L. Szuberla, John V. Olson and Kenneth M. Arnoult, Jr.

Wilson Infrasound ObservatoriesGeophysical Institute, University of Alaska Fairbanks

Presented at the Infrasound Technology WorkshopHamilton Parish, Bermuda 5 November 2008

This presentation does not necessarily reflect the policies or views of the United States Government.

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AbstractThe 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.

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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

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The IMS Infrasound Problem

▫Too many signals

excessive false alarms

▫Raise detection threshold

missed event

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The IMS Infrasound Problem

▫Too many signals

excessive false alarms

▫Raise detection threshold

missed event

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The IMS Infrasound Problem

▫Too many signals

excessive false alarms

▫Raise detection threshold

missed event

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The IMS Infrasound Problem

▫Too many signals

excessive false alarms

▫Raise detection threshold

missed event

▫Develop a near-field discriminant

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▫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

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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†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

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BAZ (plane wave)

sensors

source

y

x

Back Azimuth ,vt

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BAZ simulation

180 m

40 m

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srcLoc (spacetime approach)

t arrivals

source

sensors

yx

Localization: r, ,vt

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BAZ vs. srcLoc simulation

19 m 3 m

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ELVIS Experiment

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Normalized ELVIS Results

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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

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Numerical Augmentation

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Numerical Augmentation

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Numerical Augmentation

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Discriminant Effectiveness

3-km

5-km

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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