Infrasound

Simulation of infrasound waves propagating in the atmosphere   Source: BGR

Infrasound is the part of the sound spectrum which cannot be detected by the human ear. The frequency range of around 0.001 to 20 Hz looked at when measuring infrasound is comparable to the range used in seismology. Because of the large wavelengths of infrasound signals of up to several hundred kilometres, the low frequency sound spreads out over large distances with almost no losses. Infrasound is also hardly affected by topography or vegetation. The first global registration of infrasound probably took place after the eruption of Krakatau in August 1883. The sound signal generated by the explosion of this Indonesian volcano was so strong that it circled the earth more than seven times and was recorded by barometers all around the world.

The spectrum of natural and artificial infrasound sources ranges all the way from meteorological phenomena to nuclear explosions. The latter led to a renaissance in this scientific discipline: thanks to the Comprehensive Test Ban Treaty (CTBT), new stations were erected for the first time since the 1960s, and a global network was conceived – which promises to provide this research discipline with new findings. In addition to the obligations set down for this technology within the framework of the CTBT, BGR also carries out investigations in this area on the numerical simulation of sound propagation in the atmosphere, the automatic detection of low frequency acoustic signals, and the localisation of their sources.