13 Nov 2001Infrasound Workshop, Kona Array Geometry and Signal Observations David A McCormack Head of Monitoring and Analysis Geological Survey of Canada, Ottawa, Canada

13 Nov 2001Infrasound Workshop, Kona Topics IMS design array response for ‘realistic’ signals – how bad is bad? Initial studies of signal coherence as an indicator of maximum source distance

13 Nov 2001Infrasound Workshop, Kona Array Response Brown(2000) and Christie(2001) have illustrated problem of significant sidelobes in response pattern of 4-element infrasound array. Christie described response of various geometries with more elements and demonstrated superior characteristics of 7 and 8 element arrays.

13 Nov 2001Infrasound Workshop, Kona Brown(2000) Hz0.5 Hz Spatial Aliasing: DLIAR Array

13 Nov 2001Infrasound Workshop, Kona Brown (2000) – Hz2.0 Hz Spatial Aliasing: DLIAR Array

13 Nov 2001Infrasound Workshop, Kona Array Geometry

13 Nov 2001Infrasound Workshop, Kona SHUTTLE - time

13 Nov 2001Infrasound Workshop, Kona Shuttle

13 Nov 2001Infrasound Workshop, Kona Brown(2000) - 3 IS10 Winnipeg, Canada December 16, 1999 to September 1, 2000 Approximately 4200 detections N E S W microbaroms, Pacific Ocean (?) microbaroms, Hudson Bay ? mining activity, Minnesota, registers strongly on local seismic Local blasting Thunder Bay area, too small to register on local seismic ? Local blasting, Too small to register on local seismic

13 Nov 2001Infrasound Workshop, Kona Sine – 4 elements

13 Nov 2001Infrasound Workshop, Kona Sine – 7 elements

13 Nov 2001Infrasound Workshop, Kona Synthetic Signals Difficult to find narrowband real signals Synthetic Signals –Bandlimited white noise – identical on each channel – perfectly coherent –Superimposed on a bandlimited white background incoherent between channels –S/N adjustable, duration adjustable

13 Nov 2001Infrasound Workshop, Kona Synth ,4

13 Nov 2001Infrasound Workshop, Kona Synth ,7

13 Nov 2001Infrasound Workshop, Kona Synth ,4

13 Nov 2001Infrasound Workshop, Kona Synth ,7

13 Nov 2001Infrasound Workshop, Kona Summary I Even for narrow-band signals, side lobes are not large Suggests more analysis of real events is required before final decisions on cost/benefit of densification should be made

13 Nov 2001Infrasound Workshop, Kona Signal Coherence Grew out of studies of optimal array aperture for detection/location Coherence as a routinely calculated intrinsic parameter of an observed signal

13 Nov 2001Infrasound Workshop, Kona Local – time series

13 Nov 2001Infrasound Workshop, Kona Local – freq content

13 Nov 2001Infrasound Workshop, Kona Local - coherence

13 Nov 2001Infrasound Workshop, Kona MINNTAC - time

13 Nov 2001Infrasound Workshop, Kona MINNTAC – freq content

13 Nov 2001Infrasound Workshop, Kona MINNTAC - coherence

13 Nov 2001Infrasound Workshop, Kona SHUTTLE - time

13 Nov 2001Infrasound Workshop, Kona Shuttle – freq content

13 Nov 2001Infrasound Workshop, Kona Shuttle - coherence

13 Nov 2001Infrasound Workshop, Kona Pacific Freq

13 Nov 2001Infrasound Workshop, Kona Pacific Bolide Coherence

13 Nov 2001Infrasound Workshop, Kona Alberta Freq

13 Nov 2001Infrasound Workshop, Kona Alberta Bolide Coherence

13 Nov 2001Infrasound Workshop, Kona Recorded sources

13 Nov 2001Infrasound Workshop, Kona Processing Noise corrected under assumption of incoherent noise Interpolate to 1.5 km station spacing Ignore differences between radial and transverse coherence (this is wrong)

13 Nov 2001Infrasound Workshop, Kona Coherence vs distance

13 Nov 2001Infrasound Workshop, Kona Ms 7.4 Hector Mine, California Earthquake - Acoustic Arrival

13 Nov 2001Infrasound Workshop, Kona Summary II Contributions to coherence from source and path General trend of maximum coherence vs. distance May be useful for to establish maximum distance to observed source