Infrasonic Observations of Fireballs

Any shock generating mechanism in the atmosphere can generate infrasonic waves (low range propagation of low frequency sound waves; f ~ 0.02 - 20 Hz). Events can be detected as perturbations in density, temperature, particle velocity, or pressure (SNR best in pressure relative to atmosphere). Infrasound has been proven to be a reliable means of detecting bolides and can be used to obtain an estimate of bolide energy, location, event time, and source height.

Advantages

• Robust, cost effective technology for detection of blast waves from bolides

• Experience in operations and analysis from nuclear work (from the late 1950s to 1972, USAF operated an infrasonic nuclear explosion monitoring network)

• Can distinguish meteors that interact explosively with the lower atmosphere from those that produce shock waves at higher altitudes

• Nominal detection of kiloton explosions at 2000-3000 km ranges

• Global coverage for megaton explosions

• Detections at multiple stations can provide bolide locations

• Detections can be combined with seismic, hydro-acoustic and satellite detections for more complete characterization

• Automatic processing with analyst review

Equipment

Vault housing the sensor, digitizer, and RF Modem

 Solar panels, met station, and batteries at one array station

Deployed vault and sensor showing noise reduction hoses

Blue triangle represents planned microphone array, to be deployed at Elginfield site in spring
  of 2005

Research Being Done at UWO

• Bolide Energy Yield Using Infrasound Observations
  Goal: to derive an empirical method by which one can obtain bolide yields using observed infrasound measurements
  Method: by looking at signals from events that have been observed by both infrasound and satellite sensors (minimum range to source: ~250
            km), determine maximum signal amplitude, peak to peak amplitude, period at max. amplitude, integrated signal energy, and integrated
            signal energy signal to noise
  Conclusions: calibrated curves created from the results will allow event yield estimates to be determined solely from observed infrasound
            signals in the future; effects of wind are slight; bolide curve is somewhat lower than those of nuclear/chemical explosions
  Future Work: use results and relations to put limits on current theoretical predictions; improve the curves with more data; apply similar
            treatment to seismic observations of bolides by looking at air to ground coupling

• The Trajectory, Orbit, and Acoustical Analysis of the Park Forest Fireball
  Abstract can be found here. Video footage and more information on the Park Forest event can be found here.

Home