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

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Presentation on theme: "13 Nov 2001Infrasound Workshop, Kona Array Geometry and Signal Observations David A McCormack Head of Monitoring and Analysis Geological Survey of Canada,"— Presentation transcript:

1 13 Nov 2001Infrasound Workshop, Kona Array Geometry and Signal Observations David A McCormack Head of Monitoring and Analysis Geological Survey of Canada, Ottawa, Canada

2 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

3 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.

4 13 Nov 2001Infrasound Workshop, Kona Brown(2000) Hz0.5 Hz Spatial Aliasing: DLIAR Array

5 13 Nov 2001Infrasound Workshop, Kona Brown (2000) – Hz2.0 Hz Spatial Aliasing: DLIAR Array

6 13 Nov 2001Infrasound Workshop, Kona Array Geometry

7 13 Nov 2001Infrasound Workshop, Kona SHUTTLE - time

8 13 Nov 2001Infrasound Workshop, Kona Shuttle

9 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

10 13 Nov 2001Infrasound Workshop, Kona Sine – 4 elements

11 13 Nov 2001Infrasound Workshop, Kona Sine – 7 elements

12 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 13 Nov 2001Infrasound Workshop, Kona Synth ,4

14 13 Nov 2001Infrasound Workshop, Kona Synth ,7

15 13 Nov 2001Infrasound Workshop, Kona Synth ,4

16 13 Nov 2001Infrasound Workshop, Kona Synth ,7

17 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

18 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

19 13 Nov 2001Infrasound Workshop, Kona Local – time series

20 13 Nov 2001Infrasound Workshop, Kona Local – freq content

21 13 Nov 2001Infrasound Workshop, Kona Local - coherence

22 13 Nov 2001Infrasound Workshop, Kona MINNTAC - time

23 13 Nov 2001Infrasound Workshop, Kona MINNTAC – freq content

24 13 Nov 2001Infrasound Workshop, Kona MINNTAC - coherence

25 13 Nov 2001Infrasound Workshop, Kona SHUTTLE - time

26 13 Nov 2001Infrasound Workshop, Kona Shuttle – freq content

27 13 Nov 2001Infrasound Workshop, Kona Shuttle - coherence

28 13 Nov 2001Infrasound Workshop, Kona Pacific Freq

29 13 Nov 2001Infrasound Workshop, Kona Pacific Bolide Coherence

30 13 Nov 2001Infrasound Workshop, Kona Alberta Freq

31 13 Nov 2001Infrasound Workshop, Kona Alberta Bolide Coherence

32 13 Nov 2001Infrasound Workshop, Kona Recorded sources

33 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)

34 13 Nov 2001Infrasound Workshop, Kona Coherence vs distance

35 13 Nov 2001Infrasound Workshop, Kona Ms 7.4 Hector Mine, California Earthquake - Acoustic Arrival

36 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


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