infrasonic observations of chemical explosions
DESCRIPTION
Infrasonic observations of chemical explosions. Ludwik Liszka Swedish Institute of Space Physics. Swedish-Finnish Infrasound Network. Geographical coordinates of infrasound stations. Explosions:. Explosion site:. Directions and distances to the explosion site. - PowerPoint PPT PresentationTRANSCRIPT
Infrasonic observations of chemical explosions
Ludwik Liszka
Swedish Institute of Space Physics
Swedish-Finnish Infrasound Network
Geographical coordinates of infrasound stations
Name Latitude (Degs) Longitude (Degs)
Kiruna 67.8?N 20.4?E
Sodankylä 67.42N 26.39E
Jamton 65.87?N 22.51?E
Lycksele 64.61?N 18.71?E
Uppsala 59.85?N 17.61?E
Explosions:
Since 2001, during the period August 15 – September 15, destruction of explosives takes place in Northern Finland at the location 67.934N 25.834E 1 or 2 times per day. Each explosion equivalent to 10 tons TNT
Explosion site:
Directions and distances to the explosion site
Name Direction (Degrees)
Distance (km)
Kiruna 83.5 231
Sodankylä 337.9 62
Jämtön 30.8 280
Lycksele 37.3 492
Uppsala 20.8 978
This presentation will be mainly limited to two stations: Kiruna and Jämtön, located favourable with respect to the explosion site, at typical regional distances
Scalograms of typical signals at both stations, August 22, 2008
Kiruna Jämtön
Multifrequency measurements of the angle-of-arrival
List of wavelet filters Frequency band # Frequency, Hz Type of filter Centre frequency, Hz
1 <1 Low-pass .75
2 1 – 2 Band-pass 1.5
3 2 – 3 “ 2.5
4 3 – 4 “ 3.5
5 4 – 5 “ 4.5
6 >5 High-pass 5.5
Angle-of-arrival as a function of frequency, August 22, 2008
Kiruna Jämtön
Angle-of-arrival and trace velocity of the broad-band signal, September 1, 2008
Angle-of-arrival for different frequencies, September 1, 2008
Trace velocity for different frequencies, September 1, 2008
Source localization, September 1, 2008
Hilbert-Huang transform
A combination of the Hilbert transform and an empirical procedure decomposing the signal into Intrinsic Mode Functions (IMF) It has been found that the IMF1 derived from the original, broad-band signal may be used for localization purposes Reference: Huang, et al. "The empirical mode decomposition and the Hilbert spectrum for nonlinear and non-stationary time series analysis." Proc. R. Soc. Lond. A (1998) 454, 903–995
First four IMF:s on Sep 1, 2008
IMF1
IMF2
IMF3
IMF4
8 Hz
0
UT, minutes
IMF1
Hz
UT, minutes
IMF2
IMF3
IMF4
The fine structure of IMF1
Angle-of-arrival derived from the IMF1
Kiruna Jämtön
Source localization, September 1, 2008. Comparison with localization using the HHT IMF1
Standard deviations of derived latitude and longitude as a function of day no., Aug 13 – Sep 11,2008
Sodankylä radiosonde data Aug 13 – Sep 11,2008
Sound velocity EW wind NS wind
Sound velocity
EW windpositive towards W
NS windpositive towards S
A possible propagation model
Infrasound propagates in the form of discrete wave packets
Scalograms of typical signals at both stations, August 22, 2008
Kiruna Jämtön
A possible propagation model
Infrasound propagates in the form of discrete wave packets Each recorded wave packet may be described by:
Amplitude Dominating frequency Angle-of-arrival Horizontal trace velocity
At a given distance and direction from the source probability distributions of above parameters may be constructed. When the distance from the source increases the probability of observation of a wave packet decreases with the squared distance. It is why, even for distant sources short bursts of the signal may occasionally be observed.
A possible propagation model