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Preparing the Return of Infrasound Data Processing into IDC Operations

This presentation outlines the final preparation for moving infrasound data processing into operations at the International Data Centre (IDC) of the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization. It discusses the tuning of automatic infrasound processing, detection categorization, phase association, interactive review of signals, enhancement of processing, station noise characterization, amplitude computation, and atmospheric modeling. The milestones and accomplishments in this process are also highlighted.

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Preparing the Return of Infrasound Data Processing into IDC Operations

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  1. Preparing the Return of Infrasound Data Processing into IDC Operations Presented at: Infrasound Technology Workshop in Bermuda 3-7 November 2008 Nicolas Brachet, Pierrick Mialle, David Brown and John Coyne Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization Provisional Technical Secretariat / International Data Centre Vienna International Centre P.O. Box 1200 A-1400 Vienna AUSTRIA

  2. Outline of Presentation Final preparation for moving infrasound into operations Tuning the automatic infrasound processing Detection/detection categorization/phase association Interactive review of infrasound signals Enhancement of the automatic infrasound processing Station Noise characterization & Amplitude computation (cf. David Brown’s presentation) Atmospheric modeling (atm. specifications & simulation tools)

  3. Preparing the Return of Infrasound in IDC Operations

  4. Preparing the Return of Infrasound in IDC OpsMilestones • Historical Operational Milestones • September 2003: Guidelines from CTBT/WGB/TL-2/79 • “Significant effort should be directed into assessment and further development of infrasound tools for analysis. It is recognized that some existing tools (e.g. PMCC) show considerable potential for forming the basis for infrasound analysis, but are not yet in a form suitable for routine operations.” • March 2004: Infrasound are temporarily disconnected from network processing until a solution is found to reduce the number of (bogus) infrasound events in the IDC automatic bulletins. • July 2004: DFX-PMCC installed in Operations • November 2004: Detection categorization installed in Operations • July 2007: Interactive infrasound review tool (ARS-Geotool-PMCC) in Operations

  5. Preparing the Return of Infrasound in IDC OpsMilestones • And also offline development & testing work … • 2006: Use of frequency-distance attenuation curve to reduce the number of false associations of infrasound detections • 2007: Preliminary analyst procedure & guidelines for saving infrasound events (selected infra started to be added to REB) • Ongoing: Enhancement of existing automatic and interactive software … • Accomplishments in 2008 • New functions implemented in Geotool-PMCC interactive review tool • Prepare DFX-PMCC low frequency configuration for Solaris/Linux • Tune detection categorization • Work on Station Noise characterization & Amplitude computation • Tune GA to reduce the number of false associations with infra detections

  6. Preparing the Return of Infrasound in IDC OpsTuning of the Automatic Processing • Low frequency DFX-PMCC for Solaris (and Linux) • Objective: Enhanced detection capability, especially for distant events • Processing frequency bands between 0.07 and 4.0 Hz • Acceptable CPU time for Solaris machines (IDC Operations): Use of 11 frequency bands and duration of cross correlation windows between 30 and 60 seconds • Validation of the new detector configuration using the IRED* Example from IRED: Kasatochi eruption on August 8, 2008 detected at I22FR (New Caledonia), distance=8410km, signal frequency<0.1Hz *IDC Infrasound Reference Event Database

  7. Preparing the Return of Infrasound in IDC OpsTuning of the Automatic Processing 80m 1.5km Robinson Crusoe I14CL • Tuning of DFX-PMCC for oceanic infrasound stations • (I04AU, I05AU, I13CL, I14CL, I18DK, I27DE, I36NZ, I52GB, I55US) • Objective: Reduce the oversensitivity of DFX-PMCC to local ocean surf noise • IMS array configuration including very small aperture sub-arrays (~100m) may not be optimum for seaside areas 130m 110m 80m Inner sub-array at I14CL

  8. Preparing the Return of Infrasound in IDC OpsTuning of the Automatic Processing 200m 160m 180m Inner sub-array at I14CL • Tuning of DFX-PMCC for oceanic infrasound stations (cont.) • Action • Do not start DFX-PMCC processing with too small inner triplet configuration or/and • Increase the required minimum number of detecting elements in an array to ensure distant elements also contribute to the final detection solution.

  9. Preparing the Return of Infrasound in IDC OpsTuning of the Automatic Processing Results: The number of detections due to ocean surf decreased, with more stable detection attributes (back azimuth/trace velocity values) Example of I13CL (Easter Island), 26 October 2008 period 00:00-04:00UTC After tuning 74 detections related to surf and microbaroms Before tuning 131 detections related to surf and microbaroms

  10. Preparing the Return of Infrasound in IDC OpsTuning of the Automatic Processing • Tuning of network processing (GA) • Objective: reduce the number of false automatic associations with infra detections to a manageable level for analyst review (~10 to 15 automatic events per day) • Set up a testing/review environment (development LAN/InfraNet) and elaborate new infrasound criteria for GA Review signal detections & events Database All SHI events SHI events using new criteria IRED Geotool-PMCC InfraNet

  11. Preparing the Return of Infrasound in IDC OpsTuning of the Automatic Processing • Tuning of network processing (cont.) • Positive criteria: retain only certain types of infrasound associations • Large events: Events built with a minimum of arrivals from 3 primary stations (infra + eventually seismic), provided the first detected infrasound arrival is within 40 deg. • Seismic events: Events built with at least 1 seismic phase detected on infra station (+ seismic phases on seismic stations) • Significant events: Events including at least 1 significant infra detection (Cfreq between 0.4 Hz and 2.5 Hz ; family size>20 pixels ; family duration>120s), provided the first detected infrasound arrival is within 40 deg • Negative criteria: • Give zero weight to very small low frequency infrasound detections (Cfreq<0.25Hz and family size<12 pixels) • and reject events with less than 2 primary stations

  12. Preparing the Return of Infrasound in IDC OpsTuning of the Automatic Processing • Tuning of network processing (cont.) • Current statistics (on development LAN) with 37 operating infra arrays • Daily average: • 179 SEL3 events (SHI) • 45 “infra” events before GA criteria • 17 “infra” events after GA criteria (min. 5, max. 32) Before criteria After criteria

  13. Preparing the Return of Infrasound in IDC OpsTuning of the Automatic Processing Database problem Week-ends • Tuning of network processing (cont.) • Interactive review of the remaining automatic “infra” events after GA criteria Comments: • The automatic bulletin contains ~1 valid event per day (usually including only 1 infra station), • Some possible events could not be validated (built with 2 infra stations), • The number of events built with infra stations decreases during week-ends (when there are fewer large detections related to human activity)

  14. Preparing the Return of Infrasound in IDC OpsInteractive review of infrasound signals More functional interactive review tool for infrasound data (update of Geotool-PMCC) Detection background at the station (24 hour summary) Expandable panel for detection pixels (Azimuth, speed, consistency, correlation, RMS amplitude, number of detecting sensors, F-stats) Linear/Log frequency scale Azimuth Various polar plots frequency Time Wind Automatic/Manual beam forming

  15. Enhancement of the automatic infrasound processing: Atmospheric modeling - Models and tools -

  16. Enhancement of the automatic infra processingAtmospheric models available at the IDC ECMWF 160 160 160 160 120 120 120 120 Altitude (km) + 80 80 80 80 G2S-ECMWF 40 40 40 40 0 0 0 0 = Longitude in progress… latest HWM07 (Drob et al.,2008) HWM93 G2S-ECMWF Zonal winds at latitude 49N2March 2007 @15:00 GMT =

  17. Enhancement of the automatic infra processingAtmospheric models available at the IDC ECMWF 160 160 160 160 120 120 120 120 Altitude (km) 80 80 80 80 40 40 40 40 0 0 0 0 Longitude HWM93 G2S-ECMWF Meridional winds at latitude 49N 2 March 2007 @15:00 GMT = + G2S-ECMWF = in progress… HWM07

  18. Enhancement of the automatic infra processingAtmospheric modeling: Tools New tools for infra atmospheric modeling at the IDC • Application for producing G2S-ECMWF models (Drob,2007) has been ported to 64 bit Linux • In June 2008, the IDC received a new software (WASP-3D sph.*, Virieux et al.) for simulation of infrasound wave propagation in a complex heterogeneous medium • WASP-3D has been enhanced in order to integrate real-time atmospheric variability (ECMWF data) and recent wind model (HWM07) • WASP-3D should help better understand the atmospheric propagation and be used at the IDC for comparison with other tools (e.g. Taupc, InfraMAP) VT (km/s) *Windy Atmospheric Sonic Propagation 3D in Spherical Coordinates 150 200 Traveltimes (s) 0.46 Altitude (km) I26DE 800 75 0.36 1400 Distance (km) Source I26DE 360 0 240 300

  19. Enhancement of the automatic infra processingAtmospheric modeling: Case study (IRED) Source: EMSC and P.Labak 4500 km IS46 2825 km VRAC IS31 GERES IS26 Event location refined by analysts REB Location is 5km from GT SEL3 event built with 3 Infra+1 Seismic arrays Automatic location 75km from Ground Truth IS46 IS31 Explosion REB Novaky Poland Czech Rep. 4 km Slovakia Austria Hungary Novaky explosion (Slovakia), 2 March 2007 @ 15:28:04 GMT

  20. Enhancement of the automatic infra processingAtmospheric modeling: Case study (IRED) Novaky explosion, Waveforms and DFX-PMCC detections I46RU (4500 km) I26DE (350 km) I31KZ (2825 km)

  21. Enhancement of the automatic infra processingAtmospheric modeling: Case study (IRED) Novaky explosion, WASP-3D ray tracing at I26DE using different atm. models Ray tracing (color=shooting angle) I26DE Travel time curves (color=Trace velocity) I26DE 100km HWM93 100km HWM07 100km G2S-ECMWF

  22. Enhancement of the automatic infra processingAtmospheric modeling: Case study (IRED) I31KZ Only stratospheric rays are displayed HWM93 50km HWM07 50km G2S-ECMWF 50km I31KZ Novaky explosion, WASP-3D ray tracing at I31KZ using different atm. models Is branches It branches

  23. Enhancement of the automatic infra processingAtmospheric modeling: Case study (IRED) Novaky explosion, Summary of ray tracing results (observed/predicted celerity and back az. deviation)

  24. Summary Pre-requisite for moving infrasound into IDC Operations Tuning the automatic infrasound processing to reduce the number of bogus infrasound events down to a manageable level for analyst interactive review (~15 automatic infrasound events/day) Suitable tool for Interactive review of infrasound signals Analyst procedure & guidelines for building infrasound events Scheduled re-introduction of infrasound into Operations (beginning of 2009) Enhancement of the automatic infrasound processing New acquisitions at the IDC in 2008 for atmospheric modeling Atmospheric specifications: HWM2007, integration to G2S-ECMWF in progress Simulation tool: WASP-3D ray tracing Encouraging results, need for intensive testing and validation of the new models and tools on reference events (IRED)

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