Infrasoni

Infrasoni, or infrasonic waves, refer to acoustic waves with frequencies below the lower limit of human hearing, generally under 20 Hz. Because they lie outside normal hearing, infrasoni can often be detected only with specialized instruments, though strong waves can produce physical sensations.

These waves propagate differently from audible sound. In the atmosphere they can travel long distances, aided by temperature layers and wind streams that form ducts. Infrasound also travels through water and solids. Detection is typically done with networks of sensitive sensors, such as microbarometers, arranged in arrays to locate sources.

Natural sources include volcanic eruptions, earthquakes, meteor air bursts, severe weather, and large ocean waves. Human-made sources include explosions, rocket launches, industrial machinery, and aircraft operations. Because of long-range propagation, distant events can be identified from a few listening stations.

Applications span geophysics, meteorology, and biology. Infrasound is used to study atmospheric phenomena and to monitor for nuclear and other explosions; international systems, such as the Comprehensive Nuclear-Test-Ban Treaty’s International Monitoring System, rely on infrasonic sensors to detect tests. Some animals, notably elephants, communicate using infrasonic frequencies.

Interpreting infrasoni signals requires accounting for variable atmospheric conditions and background noise. Calibration and data integration are essential for accurate localization and characterization.