Infrasound detections

Infrasound detections result from the daily automatic analysis of BGR’s infrasound data. A Cross-correlation technique is used to identify coherent signals from data recorded by an infrasound array. The incoming direction, apparent velocity, amplitude and frequency content of each coherent signal is determined and summarized in lists. Moreover, if these parameters from different signals coincide within certain limits; they are associated with each other and considered as an event. 

Diagram of an infrasound detection list derived from the daily automatic analysis of infrasound array data. The continuous band around 0.25 Hz is the bearing of microbaroms in the North Atlantic. The high frequency, narrow bars indicate transient events. Source: BGR

The figure above is a diagram of the infrasound detection list for 18 October 2006. The direction of the signals detected at the I26DE infrasound array in the Bavarian Forest is shown colour-coded in the upper part of the diagram – displaying the back-azimuth. Every vertical bar corresponds to an event: the width represents the duration of the event, and the height the frequency content. The lower part of the diagram is a colour-coded display of the apparent velocity with which the signal energy passed the array elements. The apparent velocity is larger than the sound speed at ground if the signal passes the sensors non-horizontally, i.e., at a specific angle of incidence from above (arrivals refracted in the atmosphere); otherwise it is equal to the sound speed for horizontally propagating pressure waves (direct arrivals).

The example of an infrasound event from 18 October 2006 shows a mapview with bearings, a polar diagram (back-azimuth and apparent velocity), and the signals from two supersonic aircraft flying over the North Sea. In the upper diagram, these events are only depicted as broader bars around 16:20. Source: BGR

Infrasound bulletins from the previous day

The infrasound detection lists from the previous day from the I26DE, I27DE and IGADE arrays can be seen by clicking on the link. 

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