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

Infrasound Technology Workshop, Tokyo, Japan November 2007 Page 3

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

Infrasound Technology Workshop, Tokyo, Japan November 2007 Page 4

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)

Infrasound Technology Workshop, Tokyo, Japan November 2007 Page 5

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

Infrasound Technology Workshop, Tokyo, Japan November 2007 Page 6

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?

Infrasound Technology Workshop, Tokyo, Japan November 2007 Page 7

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

Infrasound Technology Workshop, Tokyo, Japan November 2007 Page 8

Experimental Array: Equipment Housing

Figure showing the organization of the electronic equipment in the plastic box and their connection to the external devices

Infrasound Technology Workshop, Tokyo, Japan November 2007 Page 9

Experimental Array: Wind Reduction System

Rosette filter configuration

Six porous hoses

Each hose 15 metres long

Infrasound Technology Workshop, Tokyo, Japan November 2007 Page 10

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

Infrasound Technology Workshop, Tokyo, Japan November 2007 Page 11

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?

Infrasound Technology Workshop, Tokyo, Japan November 2007 Page 12

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!

Infrasound Technology Workshop, Tokyo, Japan November 2007 Page 13

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?

Infrasound Technology Workshop, Tokyo, Japan November 2007 Page 14

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

Infrasound Technology Workshop, Tokyo, Japan November 2007 Page 15

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

Infrasound Technology Workshop, Tokyo, Japan November 2007 Page 16

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

Infrasound Technology Workshop, Tokyo, Japan November 2007 Page 17

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