Detection, Propagation, and Modeling

Infrasound Technology WorkshopBermuda, 2008

Detection using Infrasound and Seismic Station

Hedlin et al.• Detection of a Bolide Event using novel

configuration of Seismic and Infrasound Stations.• Locations Determined from Seismic Detections• Signals at infrasound and seismic stations well

correlated.• General characteristics of atmospheric

propagation understood, but not every detail• Acoustic to seismic coupling is variable.

Automated Detection and LocationLars Ceranna et al.,

• Again novel network configuration with IMS and auxiliary stations.

• 630,000 detections w/ 180,000 in the IMS bandpass

• Seasonal variability explained with 80% ducted in the Stratospheric waveguide

• Assumed constant Celerity in the inversion procedures.

Multiple Explosion in EuropeDavid Green et al.

• Four events investigated with multi-station detection for each.

• Again seismic information (ground-truth).• Delectability followed expected seasonal

patterns.• Observed coda for several closely spaced

events nearly identical.• Not all detections for one event could not be

predicted.

Effects of Turbulence at Long Distances + Results from ISTC project

#2845Kulichcov et al.

• Observation of disposal of missile and ordnance.

• Gravity waves/turbulence effects important consideration in network detection and location.

• Multipath arrivals modeled and understood• Excellent complement of radiosondes and

rocketsondes to resolve fine atmospheric structure.

Acoustic-Gravity Waves from MeteorsDoug Revelle

• Airwave objects• Give up on the Pierce-code (no leaky modes,

exclusively linear theory)• Bolides multiple events per year (~20-30)• Review of source function for these events• “What you assume determines what you get”.

Numerical Simulation of Attenuation and Non-linearlity

• Finite-difference time-domain (FDTD)• Refraction and attenuation depends on

frequency• Dispersion with altitude – attenuated

computed to be less than Sutherland and Bass.

Near-Field Clutter reductionSzuberla et al.

• Identify signals that are too close to be of interest

• Initial paper used the array to check for wave front curvature

• New approach add additional element at distance

InfraMonitor2.0Arrowsmith et al.

• New detector accounts for temporal variability of correlated noise.

• Signal association and location via a grid search algorithm with bounding constraints on celerity and back azimuth.

• Application to regional infrasound network and ground-truth events (ordnance disposal) in Utah.

• Improved detection and location statistics over existing approaches.

Infrasound from Railroad BridgesMcKenna et al.

• Near field portable array deployment to investigate acoustic radiation from railroad bridges.

• Highly instrumented source with supporting meteorological observations.

• Nocturnal inversion layers are important.

Time Domain Parabolic Equation to Model Ground-truth events

Gibson et al.• Incorporation of gravity wave fluctuations in

TDPE explain previously unexplained observed phases.

• Improved phase identification.• Gardener Spectrum, independent of location

and time.

Ground Truth Events from Quarry Blasts

Hee-il Lee et al.• Various industrial sources in South Korea, original

source locations near quarry region out in the ocean.• Seismo-acoustic event detection over all seasons.• Obtained ground-truth event information with

deployment of near-field array.• Reexamined detection and location with regional

information obtained improved results including local meterological information, observed celerities generally as expected.

• Surface wind fields did not seem to effect detectability.

Common Themes

• Seismo-acoustic monitoring for improved detection and location

• Internal Gravity-wave important to explain stratospheric refraction in some circumstances, also invoked to explain scattering out of elevated ducts

• Beginning to think incorporation of more detailed propagation models in detection and location location algorithms.