The KNMI operates three infrasound arrays (see figure 1). The largest and most low frequent array is located at Airforce Base Deelen, the Deelen Infrasound Array (DIA). DIA consists of 16 KNMI microbarometers configured in a 1.5 km aperture array. Most signals are generated by wind in the infrasonic domain, having frequencies between 1 and several Hz. Wind is coherent over small distances, tens of centimeters, with respect to the infrasonic signals of interest. Therefore, the atmosphere is sampled over an area rather than one point. This integration reduces the wind noise and significantly increases the signal-to-noise ratio (by a factor of ten). Wind noise reduction at DIA is achieved by connecting six porous hoses to each instrument in a spider like layout. At the KNMI in De Bilt, a six element array is installed (DBN). DBN consists of 6 electret microphones, where wind noise is reduced with perforated rings of pvc pipe. In Witteveen (WIT) an array of half the size of DBN is operated, consisting of the same sensing elements. DBN and WIT are, through their instruments and layout, more sensitive to high frequent events like sonic booms (dominant frequency between 1 and 5 Hz).

If infrasonic energy is detected by more than one of the arrays, source localization is achieved through cross bearing. An example in figure 1 is given for the far field sonic boom located above the North Sea, the best beam of DIA is shown. The individual bearings (and apparent sound velocities) are derived by frequency slowness (fp) analysis of the data. A coherent infrasonic wave traveling over the array shifts the array response. The amount of shift is controlled by the phase difference of the wave at each instrument. The white slowness vectors ( p-vector) are plotted in the three frequency slowness power plots in figure 1 for the far field sonic boom. The p-vector characterizes the event by its angle with respect to the North, called bearing or back azimuth, and its length, being the apparent sound velocity.
Based on its N shaped wave form, a near field sonic boom is localized South of the arrays. The N wave form leads to the characteristic double boom reported by observers. Compression at the front of the plane flying supersonicly and expansion at the back leads, at sufficient distance from the source, to the N wave form.
Interfering waves at Atlantic Ocean, to the West of The Netherlands, can lead to standing waves. This phenomenon coincides with large storms centers. Microbaroms are generated through the atmospheric coupling of these standing ocean waves. Microbaroms are observed over large distances and often for several days. The seismological counterpart, called microseism, are observed at the same time on seismometers. Microseism are generated by the coupling of the standing waves with the earth through the ocean floor. Both microseism and microbaroms have a characteristic frequency of two times this of the ocean waves. The amplitude of the generated pressure variations depend on the height and frequency of the ocean waves and the density of the medium through which they traveled (i.e. the earth in the microseism case and the atmosphere for microbaroms).
The unique recording of an exploding meteor in the atmosphere is shown as the best beam for DIA in the East of figure 1. The event occurred at night but the intense brightness of the bolide caused temporary day time light, following observers' reports. By conducting detailed raytracing through partly actual and empirical atmospherical models, a distance of 320 km and height of 15 km was derived for the meteor's explosion. With an estimated exploding power of 1.5 kT TNT, such an event is likely to occur approximately 7 to 8 times per year world-wide.