Sonic event near Boden See (Germany)
By Läslo Evers
An sonic event occured near the Boden See in the night of July 16. Figure 1
shows the results from the analysis of data from the Deelen Infrasound Array
(DIA). Coherent infrasonic energy
arrives at DIA around 22h02m26.6s GMT from a direction of 152.5 degrees with an
apparent sound velocity of 347.8 m/s.
Figure 1: Time domain Fisher analysis of DIA's infrasound data. Maximum
coherency in the data is found around 206 seconds after 21h59m00.60s GMT
on 2002, July 16. At this time of 22h02m26.6s, an apparent sound velocity of
347.8 m/s and back azimuth of 152.5 deg are resolved. An other
clear arrival from the same direction is present after 1.5 minutes. The data
are band pass filtered with corner frequencies of 0.3 and 5 Hz. The top frame
shows the best beam.
The event showed up at IS26 in Germany around 21h34m59.0s GMT, see figure 2.
At IS26 351.4 m/s and 255.5 deg are resolved for respectively the apparent
sound speed and the back azimuth.
Figure 2: Time domain Fisher analysis of infrasound data from IS26. The time
axis zero time is 21h34m59.0s on 2002, July 16 GMT. The first package of coherent
infrasound arrives after 1184 seconds, i.e. 21h54m43.0s.
At maximum Fisher ratio, 351.4 m/s and 255.5 deg are resolved.
Several other packages of
coherent energy come in during 300 seconds after the first arrival.
The data
are band pass filtered with corner frequencies of 0.3 and 5 Hz. The top frame
shows the best beam.
The event is localized through cross bearing somewhat NW of the Boden See, see
figure 3.
Figure 3: Cross bearing of the resolved back azimuths of DIA and IS26.
July 2002
Läslo Evers