Infrasonic waves are pressure disturbances, whose frequencies are below the hearing range of the human ear. Large explosions in the atmosphere generate infrasonic signals that may propagate thousands of kilometers, and may be recorded by sensitive pressure sensors called microbarographs. The sensors are devices which, like microphones, passively listen for any incoming signals. An array of these sensors acts as an antenna that permits the identification of the direction of arrival of an infrasonic signal, and thus facilitates the location of its source. Such an array will be deployed in the Kahalu'u forest, in a land parcel with controlled access and ideal environmental conditions.
Wind is the primary source of infrasonic noise.
Just as it is difficult to talk during a strong gale, it is also difficult to record infrasonic signals when the winds are strong. Gusts of wind travel as large eddies, and the size of these eddies usually scale with the intensity of the wind. Trees form a natural barrier that breaks up these eddies, and thus reduce infrasonic noise. The ideal site for an infrasound station is a well-forested area with low winds, minimal volcanic hazard, view to the horizon, low slope, some security, and available access. Central Kona is unique in that Mauna Loa, Mauna Kea, and Hualalai block the prevailing trade winds, so that there are effectively no trades in the area.