| The Exloo Infrasound Array
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The response is calculated by letting a monochromatic plane wave vertically incident
on the array. Doing so, travel time differences are zero since all instruments measure
the wave at the same time. We also speak of an inifite apparent sound speed or zero
slowness, with slowness being the reciprocal of the apparent sound speed. Figure 1 shows the
array response of EXL for a 0.5 and 5.0 Hz plane wave.
Figure 1: The array response as function of slowness for a 0.5 and 5.0 Hz plane wave, the black
circle is decribed by the sound speed of 330 m/s
The shown response has several important characteristics:
- The circular shape of the main lob. This means the atmosphere above the array is uniformly sampled; the array shows no directionality. The array will be equally sensitive to all infrasonic energy independent of its incoming angle.
- Side lobs are of low amplitude and located at considerable distance of the main lob. This implies a unique identification of infrasonic sources; the energy is mainly concentrated in the main lob.
- The main lob has a sharp and peaked form. This will result in a high resolution array. The resolved source characteristics, like apparent velocity and back azimuth, will have small errors.
All of these characteristics were optimized through a genetic algorithm leading to the unique
array configuration.