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November 2007Infrasound Technology Workshop, Tokyo, Japan Page 1
Presented to:Infrasound Technology WorkshopTokyo, Japan
PTS Experimental Infrasound Array
John Coyne1, Nicolas Brachet1, Paola Campus2, Pavel Martysevich2
1Software Applications SectionInternational Data Centre Division
2IMS Installation and Certification GroupInternational Monitoring System Division
Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty OrganizationProvisional Technical SecretariatVienna International CentreP.O. Box 1200A-1400 ViennaAustria
E-mail: John.Coyne@ctbto.org
Infrasound Technology Workshop, Tokyo, Japan November 2007 Page 2
Outline
Why?
What?
How?
Where?
When?
Summary
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Why?Processing technique used at the IDC has demonstrated the exceptional capability
of the IMS network for detecting a wide variety of signals
Signals include: microbaroms, ocean surf, mountain associated waves, thunderstorms, meteorites, avalanches, aurora, rockets, aircraft, mine blasts, accidental explosions, industrial noise …
Unlike earthquakes in the case of seismic data, few infrasound signals are energetic enough to be detected on a global scale by the IMS network
Detection technique used at the IDC is well adapted for detecting infrasound signals, including cases of very weak signals
The counterpart of such capability is the large number of genuine signals from a wide variety of sources
It is important to understand and categorize these infrasound signals
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Understanding and Categorizing Infrasound SignalsInfrasound Reference Event Database (IRED): Objective
• Collect, review and document infrasound events of special interest• Archive the data for each event into database tables • Use IRED for training, testing and validation purposes
Inventory IRED contains 311 events grouped in 10 categories (Nov 2007)
–Explosions (18)–Volcano eruptions (35)–Earthquakes, avalanches (53)–Meteorites and Bolides (15)–Rockets (42)–Mine and quarry blasts (125)–Aircraft (13)–Cultural noise (3)–Synthetic (1)–Military (2)
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Understanding and Categorizing Infrasound SignalsThe database contents are limited due to
difficulties in collecting metadata about the sources, as well as limited number of observations
One common procedure is to identify events originating from a given azimuth, and use available information (e.g., news, Google Earth, etc.) to look for the potential source(s)
This can lead to one or more hypotheses, which requires confirmation and further investigation
In order to test such hypotheses, the PTS is procuring a portable IMS-type infrasound array that can be temporarily deployed in a region of interest
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Experimental Array Minimum Specifications (from CTBT/PC/II/1/Add.2/Appendix X)
CHARACTERISTICS MINIMUM REQUIREMENTS Sensor type Microbarometer Number of sensors 4-element array1 Geometry Triangle with a component at the centre Spacing Triangle basis: 1 to 3 km2 Station location accuracy <100 m Relative sensor location <1 m Measured parameter Absolute3 or differential pressure Passband 0.02 to 4 Hz Sensor response Flat to pressure over the passband Sensor noise <18 dB below minimum acoustic noise4
Calibration <5% in absolute amplitude5 State of health Status data transmitted to the International
Data Centre Sampling rate >10 samples per second Resolution >1 count per 1 mPa Dynamic range >108 dB Timing accuracy <1 ms6 Standard temperature range -10oC to +45oC 7 Buffer at station or at National Data Centre >7days Data format Group of Scientific Experts format Data frame length <30 seconds Data transmission Continuous Data availability >98% Timely data availability >97% Mission-capable array >3 elements operational Acoustic filtering Noise reduction pipes (site dependent) Auxiliary data Meteorological data8
1 In case of noisy sites or when increased capability is required, number of components could be increased. 2 3 km is the recommended spacing. 3 Used for daily state of health. 4 Minimum noise level at 1 Hz : - ~5 mPa. 5 Periodicity : once per year (minimum). 6 Better than or equal to 1 ms. 7 Temperature range to be adapted for some specific sites. 8 Once per minute.
What?
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Experimental Array: Equipment Geometry
Each of the 4 sites consists of:MicrobarometerDigitizer with storage (3 months)Power supply (batteries and solar panels)Wind reduction systemMet data recorded at the central element
One set of spare equipment
Geometry of 4-element infrasound array
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Experimental Array: Equipment Housing
Figure showing the organization of the electronic equipment in the plastic box and their connection to the external devices
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Experimental Array: Wind Reduction System
Rosette filter configuration
Six porous hoses
Each hose 15 metres long
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Experimental Array: Equipment List
Quantity Equipment Station Spare Total
Microbarometer 4 1 5 Digitizer with externa GPS antenna and cable set (signal, power, GPS and configuration cables)
4 1 5
Charge controller 4 1 5 Equipment box 10 0 10 Batteries 65Ah None (purchased at the site) Solar panels 80W 8 2 10 Adjustable frames for solar panels 8 0 8 Temperature sensor 1 1 2 Wind speed sensor 1 1 2 Meteorological mast 1 0 1 Manifold (6 inlets) 4 1 5 Porous hose (each 15m long) 24 4 28 Plastic pipe or (each 1.5m long) 4 1 5 Heavy-duty rubber hose 4 1 5 Cable gland 8 2 10 Laptop 1 0 1 Alarm system 4 0 4 Lock 4 0 4 Cable for solar panel to equipment box 8 0 8 Cable for wind sensor to equipment box 4 0 4 Cable for temperature sensor to equipment box 4 0 4
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Conceptual Method of Work
Observation or idea
Discussion between PTS and prospective participants
Plan the project (dates, duration, locations, logistics, etc)
Decision made concerning the proposal
Exchange of letters (necessary paperwork)
Provide equipment (and or analysis) training to participants
Ship equipment to Country X
Transport of equipment and participants to field location
How?
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Conceptual Method of Work
Field observations (one or multiple sites)
Analyze data
Transport equipment to PTS
Document findings in a report
Present and discuss results at Infrasound Workshop
Feed Infrasound Reference Event Database
NOTE:
This list is preliminary, and discussion is welcome!
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Candidate ScenariosParticipate in controlled experiments
(e.g., planned explosions or field campaigns)
Test different field techniques and their effect on data processing(e.g., different noise reducing systems)
Investigate infrasound sources recorded by IMS stations
Where?
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Source Investigation for an IMS stationInstall IMS station
Observe reoccurring signals at IMS station
Hypothesize potential sources of infrasound signals
Propose experimental array deployment to distinguish between multiple potential sources or to verify a potential source
IMS stationPotential Source
Observed Azimuth
Experimental Array
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When?
The hardware is currently in the procurement process
Contract signature is expected before the end of 2007
Equipment should be available in 2Q 2008
First observations in 3Q 2008
Report first results at the next Infrasound Workshop
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Expected Benefits
The experimental array will provide a way to investigate and confirm infrasound sources
Provide additional meta-data for the Reference Event Database
The experimental array can also be used in controlled experiments for improving techniques
When participants will gain experience with the equipment, data analysis and interpretation, and project management
The results will increase our understanding of infrasound sources
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Summary
A sound understanding of infrasound sources is essential for interpreting infrasound signals
Many genuine signals of unknown origin are routinely observed at IMS infrasound station
The experimental array is expected to assist in understanding and categorizing infrasound signals
Equipment is being procured, and first experiment should take place in mid-2008
Initial results should be presented at the next Infrasound Workshop
Interested parties should contact us concerning future collaboration